SlideShare ist ein Scribd-Unternehmen logo
1 von 26
Downloaden Sie, um offline zu lesen
1
Chromosomal Aberrations
• The somatic (2n) and gametic (n) chromosome numbers of a
species ordinarily remain constant.
• This is due to the extremely precise mitotic and meiotic cell
division.
• Somatic cells of a diploid species contain two copies of each
chromosome, which are called homologous chromosome.
• Their gametes, therefore contain only one copy of each
chromosome, that is they contain one chromosome complement or
genome.
• Each chromosome of a genome contains a definite numbers and
kinds of genes, which are arranged in a definite sequence.
• Sometime due to mutation or spontaneous (without any known
causal factors), variation in chromosomal number or structure do
arise in nature. - Chromosomal aberrations.
• Chromosomal aberration may be grouped into two broad classes:
1. Structural and 2. Numerical 2
INTRODUCTION:
• Chromosome structure variations result from
chromosome breakage.
• Broken chromosomes tend to re-join; if there is more
than one break, rejoining occurs at random and not
necessarily with the correct ends.
• The result is structural changes in the chromosomes.
• Chromosome breakage is caused by X-rays, various
chemicals, and can also occur spontaneously.
• There are four common type of structural aberrations:
1.Deletion or Deficiency,
2.Duplication or Repeat
3.Inversion, and
4.Translocation 3
DELETION OR DEFICIENCY
Loss of a chromosome segment is known as deletion
or deficiency
It can be terminal deletion or interstitial or
intercalary deletion.
A single break near the end of the chromosome
would be expected to result in terminal deficiency.
If two breaks occur, a section may be deleted and an
intercalary deficiency created.
Terminal deficiencies might seem less complicated.
But majority of deficiencies detected are intercalary
type within the chromosome.
Deletion was the first structural aberration detected
by Bridges in 1917 from his genetic studies on X
chromosome of Drosophila. 4
5
6
Chromosome with deletion can never revert back to a normal
condition and transmitted to next generation.
In intercalary deletion, broken acentric fragment of
chromosomes appear as small chromatin bodies in cells known
as Micronuclei.
Homozygous deletion is lethal.
Heterozygous deletions can revealed a phenomenon known as
Pseudodominance /
 One copy of a gene is deleted
 So the recessive allele on the other chromosome is now
expressed
Eg., sex linked lethal and dominant notch-wing etc. in
Drosophila.
Cri-du-chat (Cat cry syndrome) of babies results from the
chromosome deficiency in the short arm of chromosome 5 .
7
•Deletion can be recognized during meiotic pairing of
homologus chromosome and during somatic pairing in
specialized tissue like salivary gland of Drosophila or during
pachytene in Maize.
•Due to intercalary deletion unpaired loop is formed.
DUPLICATION
The presence of an additional chromosome
segment, as compared to that normally present in a
nucleus is known as Duplication.
In a diploid organism, presence of a chromosome
segment in more than two copies per nucleus is
called duplication.
Four types of duplication:
1. Tandem duplication
2. Reverse tandem duplication
3. Displaced duplication
4. Translocation duplication
8
 The extra chromosome segment
may be located immediately after
the normal segment in precisely
the same orientation forms the
tandem .
 When the gene sequence in the
extra segment of a tandem in the
reverse order i.e, inverted , it is
known as reverse tandem
duplication.
 In some cases, the extra segment
may be located either on the
same chromosome or on a
different one but away from the
normal segment –termed as
displaced duplication.
 Later condition is also termed as
translocation duplication. 9
ORIGIN
 Origin of duplication involves
chromosome breakage and
reunion of chromosome segment
with its homologous chromosome.
 As a result, one of the two
homologous involved in the
production of a duplication ends
up with a deficiency, while the
other has a duplication for the
concerned segment.
 Another phenomenon, known as
unequal crossing over, also leads
to exactly the same consequences
for small chromosome segments.
 For e.g., duplication of the band
16A of X chromosome of
Drosophila produces Bar eye.
 This duplication is believed to
originate due to unequal crossing
over between the two normal X
chromosomes of female. 10
GENETIC EFFECTS
 Majority of small duplications have no phenotypic effect
 However, they provide raw material for evolutionary change
 Lead to the formation of gene families.
 A gene family consists of two or more genes that are
similar to each other derived from a common gene
ancestor ex- globin gene family whose Genes encode
proteins that bind oxygen
Tandem duplications play a major role in evolution, because
it is easy to generate extra copies of the duplicated genes
through the process of unequal crossing over. These extra
copies can then mutate to take on altered roles in the cell, or
they can become pseudogenes, inactive forms of the gene, by
mutation. 11
INVERSION
• When a segment of chromosome is oriented in the reverse
direction, such segment said to be inverted and the phenomenon
is termed as inversion.
• The existence of inversion was first detected by Strutevant and
Plunkett in 1926.
• Inversion occur when parts of chromosomes become detached ,
turn through 1800 and are reinserted in such a way that the genes
are in reversed order.
• For example, a certain segment may be broken in two places,
and the breaks may be in close proximity because of chance loop
in the chromosome.
• When they rejoin, the wrong ends may become connected.
• The part on one side of the loop connects with broken end
different from the one with which it was formerly connected.
• This leaves the other two broken ends to become attached.
• The part within the loop thus becomes turned around or invert
12
 Inversion may be classified into two types:
 PERICENTRIC - include the centromere
 PARACENTRIC - do not include the centromere
13
 Individuals with one copy of a normal chromosome and one copy of an inverted
chromosome
 Usually phenotypically normal
 Have a high probability of producing gametes that are abnormal in genetic
content
 Abnormality due to crossing-over within the inversion interval
 During meiosis I, homologous chromosomes synapse with each other
 For the normal and inversion chromosome to synapse properly, an inversion
loop must form
 If a cross-over occurs within the inversion loop, highly abnormal
chromosomes are produced
Inversions in natural populations
 In natural populations, pericentric inversions are much less frequent than
paracentric inversions.
 In many sp, however, pericentric inversions are relatively common, e.g., in
some Drosophila. Grasshoppers etc.
 Paracentric inversions appear to be very frequent in natural populations of
Zea maize etc.
INVERSION HETEROZYGOTES
14
When a paracentric inversion crosses
over with a normal chromosome, the
resulting chromosomes are an acentric, with
no centromeres, and a dicentric, with 2
centromeres.
The acentric chromosome isn't attached to
the spindle, so it gets lost during cell
division, and the dicentric is usually pulled
apart (broken) by the spindle pulling the two
centromeres in opposite directions. These
conditions are lethal.
Eg, Dicentric bridges formed in Maize
female tissue and pollen grains are sterile. 15
Crossing Over Within Inversion Interval
Generates Unequal Sets of Chromatids
PARACENTRIC INVERSION
16
When a pericentric inversion crosses over
with a normal chromosome, the resulting
chromosomes are both duplicated for some
genes and deleted for other genes. (They do
have 1 centromere apiece though). The gametes
resulting from these are aneuploid and do not
survive. Eg, Drosophila.
Thus, either kind of inversion has lethal
results when it crosses over with a normal
chromosome. The only offspring that survive
are those that didn't have a crossover. Thus
when you count the offspring you only see the
non-crossovers, so it appears that crossing over
has been suppressed. 17
Crossing Over Within Inversion Interval
Generates Unequal Sets of Chromatids
PERICENTRIC INVERSION
18
Inversions Prevent Generation of Recombinant
Offspring Genotypes
• Only parental chromosomes (non-
recombinants) will produce normal progeny
after fertilization
PARACENTRICPERICENTRIC 19
TRANSLOCATION
Integration of a chromosome segment into a nonhomologous
chromosome is known as translocation.
Three types:
1. simple translocation
2. shift
3. reciprocal translocation.
1. Simple translocation: In this case, terminal segment of a
chromosome is integrated at one end of a non-homologous
region. Simple translocations are rather rare.
2. Shift: In shift, an intercalary segment of a chromosome is
integrated within a non-homologous chromosome. Such
translocations are known in the populations of
Drosophila, Neurospora etc.
3. Reciprocal translocation: It is produced when two non-
homologous chromosomes exchange segments – i.e., segments
reciprocally transferred. Translocation of this type is most
common eg, Rhoeo, Oenothera, Tradescantia etc. 20
21
SHIFT RECIPROCAL
 In reciprocal translocations two non-homologous
chromosomes exchange genetic material
 Usually generate so-called balanced translocations
 Usually without phenotypic consequences
 Although can result in position effect.
CYTOLOGY OF TRANSLOCATION HETEROZYGOTE
 In simple translocations the transfer of genetic material
occurs in only one direction
 These are also called unbalanced translocations
 Unbalanced translocations are associated with phenotypic
abnormalities or even lethality
 Example: Familial Down Syndrome
 In this condition, the majority of chromosome 21 is attached to
chromosome 14. 22
 Individuals carrying balanced translocations have
a greater risk of producing gametes with
unbalanced combinations of chromosomes.
 This depends on the segregation pattern during
meiosis I
 During meiosis I, homologous chromosomes
synapse with each other
 For the translocated chromosome to synapse
properly, a translocation cross must form
Balanced Translocations and Gamete Production
BALANCED LETHALS AND GAMETIC
COMPLEXES
23
 Meiotic segregation can occur in one of three ways
 1. Alternate segregation
 Chromosomes on opposite sides of the translocation cross
segregate into the same cell
 Leads to balanced gametes
 Both contain a complete set of genes and are thus viable
 2. Adjacent-1 segregation
 Adjacent non-homologous chromosomes segregate into the
same cell
 Leads to unbalanced gametes
 Both have duplications and deletions and are thus inviable
 3. Adjacent-2 segregation
 Adjacent homologous chromosomes segregate into the same
cell
 Leads to unbalanced gametes
 Both have duplications and deletions and are thus inviable24
25
26
?

Weitere ähnliche Inhalte

Was ist angesagt?

Complementation test; AC-DS System in Maize
Complementation test; AC-DS System in MaizeComplementation test; AC-DS System in Maize
Complementation test; AC-DS System in MaizeAVKaaviya
 
Heterochromatin and euchromatin mains
Heterochromatin and euchromatin mainsHeterochromatin and euchromatin mains
Heterochromatin and euchromatin mainshithesh ck
 
Self incompatability in plants,pseudoalleles and isoalleles
Self incompatability in plants,pseudoalleles and isoallelesSelf incompatability in plants,pseudoalleles and isoalleles
Self incompatability in plants,pseudoalleles and isoallelesKanimoli Mathivathana
 
CYTOPLASMIC INHERITANCE WITH REFERENCETO MITOCHONDRIAL INHERITANCE IN YEAST
CYTOPLASMIC INHERITANCE WITH REFERENCETO MITOCHONDRIAL INHERITANCE IN YEASTCYTOPLASMIC INHERITANCE WITH REFERENCETO MITOCHONDRIAL INHERITANCE IN YEAST
CYTOPLASMIC INHERITANCE WITH REFERENCETO MITOCHONDRIAL INHERITANCE IN YEASTBishnuPatra1
 
Fine structure of gene
Fine structure of geneFine structure of gene
Fine structure of geneSayali28
 
genetic linkage and gene mapping
genetic linkage and gene mappinggenetic linkage and gene mapping
genetic linkage and gene mappingMahammed Faizan
 
Penetrance and expressivity.pdf
Penetrance and expressivity.pdfPenetrance and expressivity.pdf
Penetrance and expressivity.pdfChZaheer3
 
Recombination model and cytological basis of crossing over
Recombination model and cytological basis of crossing overRecombination model and cytological basis of crossing over
Recombination model and cytological basis of crossing overAlex Harley
 
Sex determination in drosophila & human
Sex determination in drosophila & humanSex determination in drosophila & human
Sex determination in drosophila & humanSambit Kumar Dwibedy
 
Holliday model of crossing over
Holliday model of crossing overHolliday model of crossing over
Holliday model of crossing overNethravathi Siri
 

Was ist angesagt? (20)

Complementation test; AC-DS System in Maize
Complementation test; AC-DS System in MaizeComplementation test; AC-DS System in Maize
Complementation test; AC-DS System in Maize
 
Heterochromatin and euchromatin mains
Heterochromatin and euchromatin mainsHeterochromatin and euchromatin mains
Heterochromatin and euchromatin mains
 
Self incompatability in plants,pseudoalleles and isoalleles
Self incompatability in plants,pseudoalleles and isoallelesSelf incompatability in plants,pseudoalleles and isoalleles
Self incompatability in plants,pseudoalleles and isoalleles
 
LINKAGE
LINKAGELINKAGE
LINKAGE
 
Gene concept
Gene conceptGene concept
Gene concept
 
CYTOPLASMIC INHERITANCE WITH REFERENCETO MITOCHONDRIAL INHERITANCE IN YEAST
CYTOPLASMIC INHERITANCE WITH REFERENCETO MITOCHONDRIAL INHERITANCE IN YEASTCYTOPLASMIC INHERITANCE WITH REFERENCETO MITOCHONDRIAL INHERITANCE IN YEAST
CYTOPLASMIC INHERITANCE WITH REFERENCETO MITOCHONDRIAL INHERITANCE IN YEAST
 
CROSSING OVER PPT
CROSSING OVER PPTCROSSING OVER PPT
CROSSING OVER PPT
 
Fine structure of gene
Fine structure of geneFine structure of gene
Fine structure of gene
 
Linkage
LinkageLinkage
Linkage
 
linkage and crossing over
linkage and crossing overlinkage and crossing over
linkage and crossing over
 
EXTRA CHROMOSOMAL INHERITANCE
EXTRA CHROMOSOMAL INHERITANCEEXTRA CHROMOSOMAL INHERITANCE
EXTRA CHROMOSOMAL INHERITANCE
 
genetic linkage and gene mapping
genetic linkage and gene mappinggenetic linkage and gene mapping
genetic linkage and gene mapping
 
Penetrance and expressivity.pdf
Penetrance and expressivity.pdfPenetrance and expressivity.pdf
Penetrance and expressivity.pdf
 
Maternal effects
Maternal effectsMaternal effects
Maternal effects
 
Extra nuclear inheritance
Extra nuclear inheritanceExtra nuclear inheritance
Extra nuclear inheritance
 
Recombination model and cytological basis of crossing over
Recombination model and cytological basis of crossing overRecombination model and cytological basis of crossing over
Recombination model and cytological basis of crossing over
 
Sex determination in drosophila & human
Sex determination in drosophila & humanSex determination in drosophila & human
Sex determination in drosophila & human
 
Sex determination in plants
Sex determination in plantsSex determination in plants
Sex determination in plants
 
Holliday model of crossing over
Holliday model of crossing overHolliday model of crossing over
Holliday model of crossing over
 
Mutation
MutationMutation
Mutation
 

Andere mochten auch

Change in chromosome structure
Change in chromosome structureChange in chromosome structure
Change in chromosome structureTauqeer786
 
Chromosomal Aberration
Chromosomal Aberration Chromosomal Aberration
Chromosomal Aberration Samchuchoo
 
Chromosomal Aberrations
Chromosomal AberrationsChromosomal Aberrations
Chromosomal Aberrationsgeeta parghi
 
Chromosomal abnormalities
Chromosomal abnormalitiesChromosomal abnormalities
Chromosomal abnormalitiesBiswajeeta Saha
 
Variation in chromosome structure and number chapter 8
Variation in chromosome structure and number  chapter 8Variation in chromosome structure and number  chapter 8
Variation in chromosome structure and number chapter 8Arshad Al-Ghafour
 
Chromosomal aberrations
Chromosomal aberrationsChromosomal aberrations
Chromosomal aberrationsOmar Jacalne
 
Structural chromosome aberrations
Structural chromosome aberrations Structural chromosome aberrations
Structural chromosome aberrations shrishaila cd
 
Chromosomal abnormalities
Chromosomal abnormalitiesChromosomal abnormalities
Chromosomal abnormalitiesAmy Allen
 
Chromosomal abnormalities
Chromosomal abnormalitiesChromosomal abnormalities
Chromosomal abnormalitiesFarhan Ali
 
chromosomal aberrations in number
chromosomal aberrations in numberchromosomal aberrations in number
chromosomal aberrations in numberAtika Noor
 
Numerical chromosomal aberrations
Numerical chromosomal aberrationsNumerical chromosomal aberrations
Numerical chromosomal aberrationsAtika Noor
 
structural chromosomal abberations and mutation
structural chromosomal abberations and mutationstructural chromosomal abberations and mutation
structural chromosomal abberations and mutationdibya ranjan
 
Chromosomal Disorder
Chromosomal DisorderChromosomal Disorder
Chromosomal Disorderguest11b5a
 
Chromosomal and Genetic abnormalities
Chromosomal and Genetic abnormalities Chromosomal and Genetic abnormalities
Chromosomal and Genetic abnormalities GOPIKA NAIR
 
Spontaneous and induced mutations
Spontaneous and induced mutationsSpontaneous and induced mutations
Spontaneous and induced mutationsSreeraj Thamban
 

Andere mochten auch (20)

Change in chromosome structure
Change in chromosome structureChange in chromosome structure
Change in chromosome structure
 
Chromosomal Aberration
Chromosomal Aberration Chromosomal Aberration
Chromosomal Aberration
 
Chromosomal Aberrations
Chromosomal AberrationsChromosomal Aberrations
Chromosomal Aberrations
 
Chromosomal abnormalities
Chromosomal abnormalitiesChromosomal abnormalities
Chromosomal abnormalities
 
Variation in chromosome structure and number chapter 8
Variation in chromosome structure and number  chapter 8Variation in chromosome structure and number  chapter 8
Variation in chromosome structure and number chapter 8
 
Chromosomal aberrations
Chromosomal aberrationsChromosomal aberrations
Chromosomal aberrations
 
4 chromosomal aberrations ks
4 chromosomal  aberrations ks4 chromosomal  aberrations ks
4 chromosomal aberrations ks
 
Structural chromosome aberrations
Structural chromosome aberrations Structural chromosome aberrations
Structural chromosome aberrations
 
Chromosomal abnormalities
Chromosomal abnormalitiesChromosomal abnormalities
Chromosomal abnormalities
 
Chromosomal Disorders
Chromosomal DisordersChromosomal Disorders
Chromosomal Disorders
 
Chromosomal abnormalities
Chromosomal abnormalitiesChromosomal abnormalities
Chromosomal abnormalities
 
chromosomal aberrations in number
chromosomal aberrations in numberchromosomal aberrations in number
chromosomal aberrations in number
 
Numerical chromosomal aberrations
Numerical chromosomal aberrationsNumerical chromosomal aberrations
Numerical chromosomal aberrations
 
Chromosomal variation
Chromosomal variationChromosomal variation
Chromosomal variation
 
structural chromosomal abberations and mutation
structural chromosomal abberations and mutationstructural chromosomal abberations and mutation
structural chromosomal abberations and mutation
 
Chromosomal Disorder
Chromosomal DisorderChromosomal Disorder
Chromosomal Disorder
 
Chromosomal and Genetic abnormalities
Chromosomal and Genetic abnormalities Chromosomal and Genetic abnormalities
Chromosomal and Genetic abnormalities
 
Spontaneous and induced mutations
Spontaneous and induced mutationsSpontaneous and induced mutations
Spontaneous and induced mutations
 
Chromosomes
ChromosomesChromosomes
Chromosomes
 
Mutations powerpoint
Mutations powerpointMutations powerpoint
Mutations powerpoint
 

Ähnlich wie Structural changes in chromosomes

Structural Chromosome aberration ppt
 Structural Chromosome aberration ppt Structural Chromosome aberration ppt
Structural Chromosome aberration pptUpayan1234
 
Variation of chromosomes
Variation of chromosomesVariation of chromosomes
Variation of chromosomesneelotpal31
 
Chromosomal aberrations or mutations
Chromosomal aberrations or mutationsChromosomal aberrations or mutations
Chromosomal aberrations or mutationszubair saqib
 
CHROMOSOME and CHROMOSOMAL ABERRATIONS
CHROMOSOME and CHROMOSOMAL ABERRATIONS CHROMOSOME and CHROMOSOMAL ABERRATIONS
CHROMOSOME and CHROMOSOMAL ABERRATIONS Gauravrajsinh Vaghela
 
Chromosomal aberrations, utilization of aneuploids, chimeras and role of allo...
Chromosomal aberrations, utilization of aneuploids, chimeras and role of allo...Chromosomal aberrations, utilization of aneuploids, chimeras and role of allo...
Chromosomal aberrations, utilization of aneuploids, chimeras and role of allo...GauravRajSinhVaghela
 
Translocation.pdf
Translocation.pdfTranslocation.pdf
Translocation.pdfMuskan92573
 
Chromosomal Mutation.pptx
Chromosomal Mutation.pptxChromosomal Mutation.pptx
Chromosomal Mutation.pptxEhtishamShah7
 
Presentation on Structural Chromosomal Aberrations
Presentation on Structural Chromosomal AberrationsPresentation on Structural Chromosomal Aberrations
Presentation on Structural Chromosomal AberrationsDr. Kaushik Kumar Panigrahi
 
Structural Chromosomal aberrations (Change in Structure of Chromosome)
Structural Chromosomal aberrations (Change in Structure of Chromosome)Structural Chromosomal aberrations (Change in Structure of Chromosome)
Structural Chromosomal aberrations (Change in Structure of Chromosome)Asad Afridi
 
linkage-and-crossing-over.pdf
linkage-and-crossing-over.pdflinkage-and-crossing-over.pdf
linkage-and-crossing-over.pdfTaiyeb1
 
Chromosomal aberrations (structural)
Chromosomal aberrations (structural)Chromosomal aberrations (structural)
Chromosomal aberrations (structural)GURUNath18
 

Ähnlich wie Structural changes in chromosomes (20)

Structural Chromosome aberration ppt
 Structural Chromosome aberration ppt Structural Chromosome aberration ppt
Structural Chromosome aberration ppt
 
Variation of chromosomes
Variation of chromosomesVariation of chromosomes
Variation of chromosomes
 
Chromosomal aberrations or mutations
Chromosomal aberrations or mutationsChromosomal aberrations or mutations
Chromosomal aberrations or mutations
 
CHROMOSOME and CHROMOSOMAL ABERRATIONS
CHROMOSOME and CHROMOSOMAL ABERRATIONS CHROMOSOME and CHROMOSOMAL ABERRATIONS
CHROMOSOME and CHROMOSOMAL ABERRATIONS
 
Chromosomal aberrations, utilization of aneuploids, chimeras and role of allo...
Chromosomal aberrations, utilization of aneuploids, chimeras and role of allo...Chromosomal aberrations, utilization of aneuploids, chimeras and role of allo...
Chromosomal aberrations, utilization of aneuploids, chimeras and role of allo...
 
chromosomes variation
chromosomes variationchromosomes variation
chromosomes variation
 
Inversions
InversionsInversions
Inversions
 
Chromosome
ChromosomeChromosome
Chromosome
 
Genetics
GeneticsGenetics
Genetics
 
Translocation.pdf
Translocation.pdfTranslocation.pdf
Translocation.pdf
 
Chromosomal Mutation.pptx
Chromosomal Mutation.pptxChromosomal Mutation.pptx
Chromosomal Mutation.pptx
 
Gen lec!
Gen lec!Gen lec!
Gen lec!
 
Presentation on Structural Chromosomal Aberrations
Presentation on Structural Chromosomal AberrationsPresentation on Structural Chromosomal Aberrations
Presentation on Structural Chromosomal Aberrations
 
Structural Chromosomal aberrations (Change in Structure of Chromosome)
Structural Chromosomal aberrations (Change in Structure of Chromosome)Structural Chromosomal aberrations (Change in Structure of Chromosome)
Structural Chromosomal aberrations (Change in Structure of Chromosome)
 
Genetics 2.pdf
Genetics 2.pdfGenetics 2.pdf
Genetics 2.pdf
 
Genetics
GeneticsGenetics
Genetics
 
Genetics
GeneticsGenetics
Genetics
 
linkage-and-crossing-over.pdf
linkage-and-crossing-over.pdflinkage-and-crossing-over.pdf
linkage-and-crossing-over.pdf
 
Chromosomal aberrations
Chromosomal aberrationsChromosomal aberrations
Chromosomal aberrations
 
Chromosomal aberrations (structural)
Chromosomal aberrations (structural)Chromosomal aberrations (structural)
Chromosomal aberrations (structural)
 

Kürzlich hochgeladen

5 charts on South Africa as a source country for international student recrui...
5 charts on South Africa as a source country for international student recrui...5 charts on South Africa as a source country for international student recrui...
5 charts on South Africa as a source country for international student recrui...CaraSkikne1
 
3.21.24 The Origins of Black Power.pptx
3.21.24  The Origins of Black Power.pptx3.21.24  The Origins of Black Power.pptx
3.21.24 The Origins of Black Power.pptxmary850239
 
Education and training program in the hospital APR.pptx
Education and training program in the hospital APR.pptxEducation and training program in the hospital APR.pptx
Education and training program in the hospital APR.pptxraviapr7
 
Patterns of Written Texts Across Disciplines.pptx
Patterns of Written Texts Across Disciplines.pptxPatterns of Written Texts Across Disciplines.pptx
Patterns of Written Texts Across Disciplines.pptxMYDA ANGELICA SUAN
 
Prescribed medication order and communication skills.pptx
Prescribed medication order and communication skills.pptxPrescribed medication order and communication skills.pptx
Prescribed medication order and communication skills.pptxraviapr7
 
Ultra structure and life cycle of Plasmodium.pptx
Ultra structure and life cycle of Plasmodium.pptxUltra structure and life cycle of Plasmodium.pptx
Ultra structure and life cycle of Plasmodium.pptxDr. Asif Anas
 
DUST OF SNOW_BY ROBERT FROST_EDITED BY_ TANMOY MISHRA
DUST OF SNOW_BY ROBERT FROST_EDITED BY_ TANMOY MISHRADUST OF SNOW_BY ROBERT FROST_EDITED BY_ TANMOY MISHRA
DUST OF SNOW_BY ROBERT FROST_EDITED BY_ TANMOY MISHRATanmoy Mishra
 
2024.03.23 What do successful readers do - Sandy Millin for PARK.pptx
2024.03.23 What do successful readers do - Sandy Millin for PARK.pptx2024.03.23 What do successful readers do - Sandy Millin for PARK.pptx
2024.03.23 What do successful readers do - Sandy Millin for PARK.pptxSandy Millin
 
How to Add a many2many Relational Field in Odoo 17
How to Add a many2many Relational Field in Odoo 17How to Add a many2many Relational Field in Odoo 17
How to Add a many2many Relational Field in Odoo 17Celine George
 
M-2- General Reactions of amino acids.pptx
M-2- General Reactions of amino acids.pptxM-2- General Reactions of amino acids.pptx
M-2- General Reactions of amino acids.pptxDr. Santhosh Kumar. N
 
What is the Future of QuickBooks DeskTop?
What is the Future of QuickBooks DeskTop?What is the Future of QuickBooks DeskTop?
What is the Future of QuickBooks DeskTop?TechSoup
 
Presentation on the Basics of Writing. Writing a Paragraph
Presentation on the Basics of Writing. Writing a ParagraphPresentation on the Basics of Writing. Writing a Paragraph
Presentation on the Basics of Writing. Writing a ParagraphNetziValdelomar1
 
Philosophy of Education and Educational Philosophy
Philosophy of Education  and Educational PhilosophyPhilosophy of Education  and Educational Philosophy
Philosophy of Education and Educational PhilosophyShuvankar Madhu
 
CapTechU Doctoral Presentation -March 2024 slides.pptx
CapTechU Doctoral Presentation -March 2024 slides.pptxCapTechU Doctoral Presentation -March 2024 slides.pptx
CapTechU Doctoral Presentation -March 2024 slides.pptxCapitolTechU
 
The basics of sentences session 10pptx.pptx
The basics of sentences session 10pptx.pptxThe basics of sentences session 10pptx.pptx
The basics of sentences session 10pptx.pptxheathfieldcps1
 
Practical Research 1 Lesson 9 Scope and delimitation.pptx
Practical Research 1 Lesson 9 Scope and delimitation.pptxPractical Research 1 Lesson 9 Scope and delimitation.pptx
Practical Research 1 Lesson 9 Scope and delimitation.pptxKatherine Villaluna
 
Human-AI Co-Creation of Worked Examples for Programming Classes
Human-AI Co-Creation of Worked Examples for Programming ClassesHuman-AI Co-Creation of Worked Examples for Programming Classes
Human-AI Co-Creation of Worked Examples for Programming ClassesMohammad Hassany
 
The Singapore Teaching Practice document
The Singapore Teaching Practice documentThe Singapore Teaching Practice document
The Singapore Teaching Practice documentXsasf Sfdfasd
 
Quality Assurance_GOOD LABORATORY PRACTICE
Quality Assurance_GOOD LABORATORY PRACTICEQuality Assurance_GOOD LABORATORY PRACTICE
Quality Assurance_GOOD LABORATORY PRACTICESayali Powar
 

Kürzlich hochgeladen (20)

5 charts on South Africa as a source country for international student recrui...
5 charts on South Africa as a source country for international student recrui...5 charts on South Africa as a source country for international student recrui...
5 charts on South Africa as a source country for international student recrui...
 
3.21.24 The Origins of Black Power.pptx
3.21.24  The Origins of Black Power.pptx3.21.24  The Origins of Black Power.pptx
3.21.24 The Origins of Black Power.pptx
 
Education and training program in the hospital APR.pptx
Education and training program in the hospital APR.pptxEducation and training program in the hospital APR.pptx
Education and training program in the hospital APR.pptx
 
Patterns of Written Texts Across Disciplines.pptx
Patterns of Written Texts Across Disciplines.pptxPatterns of Written Texts Across Disciplines.pptx
Patterns of Written Texts Across Disciplines.pptx
 
Prescribed medication order and communication skills.pptx
Prescribed medication order and communication skills.pptxPrescribed medication order and communication skills.pptx
Prescribed medication order and communication skills.pptx
 
Ultra structure and life cycle of Plasmodium.pptx
Ultra structure and life cycle of Plasmodium.pptxUltra structure and life cycle of Plasmodium.pptx
Ultra structure and life cycle of Plasmodium.pptx
 
DUST OF SNOW_BY ROBERT FROST_EDITED BY_ TANMOY MISHRA
DUST OF SNOW_BY ROBERT FROST_EDITED BY_ TANMOY MISHRADUST OF SNOW_BY ROBERT FROST_EDITED BY_ TANMOY MISHRA
DUST OF SNOW_BY ROBERT FROST_EDITED BY_ TANMOY MISHRA
 
2024.03.23 What do successful readers do - Sandy Millin for PARK.pptx
2024.03.23 What do successful readers do - Sandy Millin for PARK.pptx2024.03.23 What do successful readers do - Sandy Millin for PARK.pptx
2024.03.23 What do successful readers do - Sandy Millin for PARK.pptx
 
How to Add a many2many Relational Field in Odoo 17
How to Add a many2many Relational Field in Odoo 17How to Add a many2many Relational Field in Odoo 17
How to Add a many2many Relational Field in Odoo 17
 
Personal Resilience in Project Management 2 - TV Edit 1a.pdf
Personal Resilience in Project Management 2 - TV Edit 1a.pdfPersonal Resilience in Project Management 2 - TV Edit 1a.pdf
Personal Resilience in Project Management 2 - TV Edit 1a.pdf
 
M-2- General Reactions of amino acids.pptx
M-2- General Reactions of amino acids.pptxM-2- General Reactions of amino acids.pptx
M-2- General Reactions of amino acids.pptx
 
What is the Future of QuickBooks DeskTop?
What is the Future of QuickBooks DeskTop?What is the Future of QuickBooks DeskTop?
What is the Future of QuickBooks DeskTop?
 
Presentation on the Basics of Writing. Writing a Paragraph
Presentation on the Basics of Writing. Writing a ParagraphPresentation on the Basics of Writing. Writing a Paragraph
Presentation on the Basics of Writing. Writing a Paragraph
 
Philosophy of Education and Educational Philosophy
Philosophy of Education  and Educational PhilosophyPhilosophy of Education  and Educational Philosophy
Philosophy of Education and Educational Philosophy
 
CapTechU Doctoral Presentation -March 2024 slides.pptx
CapTechU Doctoral Presentation -March 2024 slides.pptxCapTechU Doctoral Presentation -March 2024 slides.pptx
CapTechU Doctoral Presentation -March 2024 slides.pptx
 
The basics of sentences session 10pptx.pptx
The basics of sentences session 10pptx.pptxThe basics of sentences session 10pptx.pptx
The basics of sentences session 10pptx.pptx
 
Practical Research 1 Lesson 9 Scope and delimitation.pptx
Practical Research 1 Lesson 9 Scope and delimitation.pptxPractical Research 1 Lesson 9 Scope and delimitation.pptx
Practical Research 1 Lesson 9 Scope and delimitation.pptx
 
Human-AI Co-Creation of Worked Examples for Programming Classes
Human-AI Co-Creation of Worked Examples for Programming ClassesHuman-AI Co-Creation of Worked Examples for Programming Classes
Human-AI Co-Creation of Worked Examples for Programming Classes
 
The Singapore Teaching Practice document
The Singapore Teaching Practice documentThe Singapore Teaching Practice document
The Singapore Teaching Practice document
 
Quality Assurance_GOOD LABORATORY PRACTICE
Quality Assurance_GOOD LABORATORY PRACTICEQuality Assurance_GOOD LABORATORY PRACTICE
Quality Assurance_GOOD LABORATORY PRACTICE
 

Structural changes in chromosomes

  • 1. 1
  • 2. Chromosomal Aberrations • The somatic (2n) and gametic (n) chromosome numbers of a species ordinarily remain constant. • This is due to the extremely precise mitotic and meiotic cell division. • Somatic cells of a diploid species contain two copies of each chromosome, which are called homologous chromosome. • Their gametes, therefore contain only one copy of each chromosome, that is they contain one chromosome complement or genome. • Each chromosome of a genome contains a definite numbers and kinds of genes, which are arranged in a definite sequence. • Sometime due to mutation or spontaneous (without any known causal factors), variation in chromosomal number or structure do arise in nature. - Chromosomal aberrations. • Chromosomal aberration may be grouped into two broad classes: 1. Structural and 2. Numerical 2
  • 3. INTRODUCTION: • Chromosome structure variations result from chromosome breakage. • Broken chromosomes tend to re-join; if there is more than one break, rejoining occurs at random and not necessarily with the correct ends. • The result is structural changes in the chromosomes. • Chromosome breakage is caused by X-rays, various chemicals, and can also occur spontaneously. • There are four common type of structural aberrations: 1.Deletion or Deficiency, 2.Duplication or Repeat 3.Inversion, and 4.Translocation 3
  • 4. DELETION OR DEFICIENCY Loss of a chromosome segment is known as deletion or deficiency It can be terminal deletion or interstitial or intercalary deletion. A single break near the end of the chromosome would be expected to result in terminal deficiency. If two breaks occur, a section may be deleted and an intercalary deficiency created. Terminal deficiencies might seem less complicated. But majority of deficiencies detected are intercalary type within the chromosome. Deletion was the first structural aberration detected by Bridges in 1917 from his genetic studies on X chromosome of Drosophila. 4
  • 5. 5
  • 6. 6 Chromosome with deletion can never revert back to a normal condition and transmitted to next generation. In intercalary deletion, broken acentric fragment of chromosomes appear as small chromatin bodies in cells known as Micronuclei. Homozygous deletion is lethal. Heterozygous deletions can revealed a phenomenon known as Pseudodominance /  One copy of a gene is deleted  So the recessive allele on the other chromosome is now expressed Eg., sex linked lethal and dominant notch-wing etc. in Drosophila. Cri-du-chat (Cat cry syndrome) of babies results from the chromosome deficiency in the short arm of chromosome 5 .
  • 7. 7 •Deletion can be recognized during meiotic pairing of homologus chromosome and during somatic pairing in specialized tissue like salivary gland of Drosophila or during pachytene in Maize. •Due to intercalary deletion unpaired loop is formed.
  • 8. DUPLICATION The presence of an additional chromosome segment, as compared to that normally present in a nucleus is known as Duplication. In a diploid organism, presence of a chromosome segment in more than two copies per nucleus is called duplication. Four types of duplication: 1. Tandem duplication 2. Reverse tandem duplication 3. Displaced duplication 4. Translocation duplication 8
  • 9.  The extra chromosome segment may be located immediately after the normal segment in precisely the same orientation forms the tandem .  When the gene sequence in the extra segment of a tandem in the reverse order i.e, inverted , it is known as reverse tandem duplication.  In some cases, the extra segment may be located either on the same chromosome or on a different one but away from the normal segment –termed as displaced duplication.  Later condition is also termed as translocation duplication. 9
  • 10. ORIGIN  Origin of duplication involves chromosome breakage and reunion of chromosome segment with its homologous chromosome.  As a result, one of the two homologous involved in the production of a duplication ends up with a deficiency, while the other has a duplication for the concerned segment.  Another phenomenon, known as unequal crossing over, also leads to exactly the same consequences for small chromosome segments.  For e.g., duplication of the band 16A of X chromosome of Drosophila produces Bar eye.  This duplication is believed to originate due to unequal crossing over between the two normal X chromosomes of female. 10
  • 11. GENETIC EFFECTS  Majority of small duplications have no phenotypic effect  However, they provide raw material for evolutionary change  Lead to the formation of gene families.  A gene family consists of two or more genes that are similar to each other derived from a common gene ancestor ex- globin gene family whose Genes encode proteins that bind oxygen Tandem duplications play a major role in evolution, because it is easy to generate extra copies of the duplicated genes through the process of unequal crossing over. These extra copies can then mutate to take on altered roles in the cell, or they can become pseudogenes, inactive forms of the gene, by mutation. 11
  • 12. INVERSION • When a segment of chromosome is oriented in the reverse direction, such segment said to be inverted and the phenomenon is termed as inversion. • The existence of inversion was first detected by Strutevant and Plunkett in 1926. • Inversion occur when parts of chromosomes become detached , turn through 1800 and are reinserted in such a way that the genes are in reversed order. • For example, a certain segment may be broken in two places, and the breaks may be in close proximity because of chance loop in the chromosome. • When they rejoin, the wrong ends may become connected. • The part on one side of the loop connects with broken end different from the one with which it was formerly connected. • This leaves the other two broken ends to become attached. • The part within the loop thus becomes turned around or invert 12
  • 13.  Inversion may be classified into two types:  PERICENTRIC - include the centromere  PARACENTRIC - do not include the centromere 13
  • 14.  Individuals with one copy of a normal chromosome and one copy of an inverted chromosome  Usually phenotypically normal  Have a high probability of producing gametes that are abnormal in genetic content  Abnormality due to crossing-over within the inversion interval  During meiosis I, homologous chromosomes synapse with each other  For the normal and inversion chromosome to synapse properly, an inversion loop must form  If a cross-over occurs within the inversion loop, highly abnormal chromosomes are produced Inversions in natural populations  In natural populations, pericentric inversions are much less frequent than paracentric inversions.  In many sp, however, pericentric inversions are relatively common, e.g., in some Drosophila. Grasshoppers etc.  Paracentric inversions appear to be very frequent in natural populations of Zea maize etc. INVERSION HETEROZYGOTES 14
  • 15. When a paracentric inversion crosses over with a normal chromosome, the resulting chromosomes are an acentric, with no centromeres, and a dicentric, with 2 centromeres. The acentric chromosome isn't attached to the spindle, so it gets lost during cell division, and the dicentric is usually pulled apart (broken) by the spindle pulling the two centromeres in opposite directions. These conditions are lethal. Eg, Dicentric bridges formed in Maize female tissue and pollen grains are sterile. 15
  • 16. Crossing Over Within Inversion Interval Generates Unequal Sets of Chromatids PARACENTRIC INVERSION 16
  • 17. When a pericentric inversion crosses over with a normal chromosome, the resulting chromosomes are both duplicated for some genes and deleted for other genes. (They do have 1 centromere apiece though). The gametes resulting from these are aneuploid and do not survive. Eg, Drosophila. Thus, either kind of inversion has lethal results when it crosses over with a normal chromosome. The only offspring that survive are those that didn't have a crossover. Thus when you count the offspring you only see the non-crossovers, so it appears that crossing over has been suppressed. 17
  • 18. Crossing Over Within Inversion Interval Generates Unequal Sets of Chromatids PERICENTRIC INVERSION 18
  • 19. Inversions Prevent Generation of Recombinant Offspring Genotypes • Only parental chromosomes (non- recombinants) will produce normal progeny after fertilization PARACENTRICPERICENTRIC 19
  • 20. TRANSLOCATION Integration of a chromosome segment into a nonhomologous chromosome is known as translocation. Three types: 1. simple translocation 2. shift 3. reciprocal translocation. 1. Simple translocation: In this case, terminal segment of a chromosome is integrated at one end of a non-homologous region. Simple translocations are rather rare. 2. Shift: In shift, an intercalary segment of a chromosome is integrated within a non-homologous chromosome. Such translocations are known in the populations of Drosophila, Neurospora etc. 3. Reciprocal translocation: It is produced when two non- homologous chromosomes exchange segments – i.e., segments reciprocally transferred. Translocation of this type is most common eg, Rhoeo, Oenothera, Tradescantia etc. 20
  • 22.  In reciprocal translocations two non-homologous chromosomes exchange genetic material  Usually generate so-called balanced translocations  Usually without phenotypic consequences  Although can result in position effect. CYTOLOGY OF TRANSLOCATION HETEROZYGOTE  In simple translocations the transfer of genetic material occurs in only one direction  These are also called unbalanced translocations  Unbalanced translocations are associated with phenotypic abnormalities or even lethality  Example: Familial Down Syndrome  In this condition, the majority of chromosome 21 is attached to chromosome 14. 22
  • 23.  Individuals carrying balanced translocations have a greater risk of producing gametes with unbalanced combinations of chromosomes.  This depends on the segregation pattern during meiosis I  During meiosis I, homologous chromosomes synapse with each other  For the translocated chromosome to synapse properly, a translocation cross must form Balanced Translocations and Gamete Production BALANCED LETHALS AND GAMETIC COMPLEXES 23
  • 24.  Meiotic segregation can occur in one of three ways  1. Alternate segregation  Chromosomes on opposite sides of the translocation cross segregate into the same cell  Leads to balanced gametes  Both contain a complete set of genes and are thus viable  2. Adjacent-1 segregation  Adjacent non-homologous chromosomes segregate into the same cell  Leads to unbalanced gametes  Both have duplications and deletions and are thus inviable  3. Adjacent-2 segregation  Adjacent homologous chromosomes segregate into the same cell  Leads to unbalanced gametes  Both have duplications and deletions and are thus inviable24
  • 25. 25
  • 26. 26 ?