Notes kuliah1 aqu2203 sem_i 201213d

1

AQU2203
Teknik Pembiakbakaan Ikan

Lecture 1
Introduction to Genetics

© Dr. Shahreza, FPAI, UMT

AQU2203 Teknik Pembiakbakaan Ikan 2

Lecture 1

Objective :

1) To expose students to the basic concepts of
genetic and its relation to fish breeding.

2) To develop understanding about genetic
approach in fish production.



Lecture 1

Lecture Content :

Basic concepts of genetics.
Gene
Phenotype and Genotype.
Gene Interaction



Lecture 1
Concepts of Genetics
Learning Outcome :

At the end of lecture, students should be able to :

Explain how certain traits are produced and
inherited in fish

Characterize the types of phenotypes

Differentiate the gene interaction

Fish like all living organisms, reproduce and
inherit their traits from one generation to the
other
It involve several processes which
ensures that their genetic information
are maintained and passed on to the
next generation.
These information are found in
the DNA which is located in the
Zygote cell.

Egg

Fertilization Sperm


Cell

DNA contains all the biological information of an organism
(e.g. type of body colour, scale, pattern, fin, shape)


 Organisms are made up of billions of cells

 These cells carry all the information about the
biological functions of an organism

 Genetic information is located in the double helix
structure called DNA (Deoxyribonucleic Acid)

 DNA is a chemical structure that forms Chromosome

 Consist of sequence of bases and nucleotides :
(Adenine (A), Guanine (G), Thymine (T) dan Cytosine
(C)) in a double helix structure.

 Genetic information is coded in the different
arrangements of these 4 nucleotides.

 Contains various sequence that can be identified
through various methods in the study of DNA.

 All living things are made up of DNA



A field of science about hereditary and variation

Studies the inheritance scientifically

A science about gene



Flesh Quality

Body colour

GENE
Controls various biological function in
organism
Growth
Body shape
Disease resistance



What is a Gene ?
Sequence of DNA that codes for a certain
function (protein, biochemical process,
physical characteristics) in an organism

Basic unit of hereditary information that can be inherited from
one generation to the other.

It is made of DNA :
- Consist of DNA sequence (nucleotides that codes for a
certain function)
Exist in a chemical structure of a DNA molecule



In an organism, genes are
carried on a chromosome that
is found in the nucleus of
each cell

Location of a gene on a
chromosome is called locus



A gene or set of genes contains the blueprints or chemical instructions
for the production of a protein.

Proteins – forms or helps produce various phenotypes (body colour,
shape, sex, number of rays, body length)



How a Characteristics
of an Organism is
Expressed

Protein

Trancription
DNA RNA
Translation


Genotype
Gene that controls a
particular phenotype of an
organism
Acts together with
environmental factors to form
a certain phenotype

Phenotype
The physical characteristics that is
expressed by a particular gene or a
group of genes

Can be divided into :
- Qualitative Phenotype
- Quantitave Phenotype


Qualitative Phenotype
Phenotypes that can be described – colour, sex,
scale and colour pattern

Usually controlled by one or two genes

An alternative form of a phenotype is produced
by an alternative form of a gene (allele)



Different body colouration are due to
different allele of colour genes



Qualitative Phenotype – Autosomal

Phenotype that is controlled by genes located on an autosome
They are not related with sex
Autosomal genes are inherited and expressed equally in male
and female



Qualitative Phenotype – Autosomal

Body colouration and pattern in some fishes
are not controlled by sex and are expressed
equally in males and females


Qualitative Phenotype – Sex-Linked
Phenotype that is controlled by genes located on a
chromosome that controls sex

Sex-linked genes are inherited and expressed differently in
male and female

Mostly identified in
ornamental fish.

e.g. body colour, fin shape



Qualitative Phenotype – Sex-Linked
Body colouration and fin shape in
some fishes are controlled by sex
and are expressed differently in
males and females

Swordtail

Guppy



Quantitative Phenotype
Phenotypes that are measured – length, weight, feed
conversion

Usually controlled by many genes (up to hundreds of genes)

Strongly influenced by environmental variables (size, age,
stocking density and water condition)



Quantitative Phenotype – Sex-Linked
Body size in some fishes are
controlled by sex and are expressed
differently in males and females
Example :
Male Tilapia and grouper are bigger
compared to female

Grouper

Tilapia



SPERMATOGENESIS

2N Spermatogonium

Mitosis

2N Primary Spermatocyte
2N

First Meiotic Division

N N Secondary Spermatocyte
(haploid)
Second Meiotic
Division
N N N N Spermatid (haploid)

N N N N Sperm (haploid)



OOGENESIS

2N Oogonium

Mitosis

2N 2N Primary Oocyte

First Meiotic Division

N Secondary Oocyte and
N First Polar Body
Second Meiotic
Division

N N
N
Ovum dan Second N
Polar Body



Fertilization Gamete (n)
Gamete (n)
Female Male

Zygote (2n)


Cell Replication Formation of Gametes

Involves Mitosis and Meiosis

•Affect gene interaction and inheritance
•Can be manipulated


Expression of a phenotype is caused by reaction of 1 or a pair of
allele in the genome of an organism

Occurs due to reaction of a gene or a group of genes that is
responsible towards a specific phenotypic characteristics

Interaction of a
Interaction of a group of alleles
2N 2N
pair of allele


Gene can be expressed in an additive or non-additive manner

Each allele contributes equally One allele (dominant allele) is
to the production of the expressed more strongly than
phenotype the other allele (recessive
allele)

Equally >
Expressed or
<
2N 2N


Gene action will give variation in the phenotypic expression of an organism

Phenotypic expression can be divided into 2 major catogories :
Qualitative Phenotype and Quantitative Phenotype

The result of gene action can be analyzed and determined

Example : Example :
Colours, sex, scale pattern Length, weight



Most qualitative phenotypes are controlled by single autosomal genes
with 2 alleles per locus

Qualitative phenotypes can also be controlled by 2 autosomal genes
(example : scale pattern of common carp; body colour of fighting fish)

Different genotype will produce clearly define different phenotype

The genetic of qualitative phenotypes is simple and is often called
”Mendelian Genetics”.

Single autosomal gene
2 autosomal gene with
with 2 alleles per locus
2 alleles per locus

2N 2N


Complete Incomplete
Dominant Dominant

Additive



Occurs when a strong dominant allele produces phenotype regardless of
the genotype.

Recessive allele only produced its phenotypic characteristics when no
dominant allele is present.

Locus which has 2 dominant alleles will produce only 1 phenotype.

Dominant gene action can produce 3 genotypes and 2 phenotypes

Genotype Phenotype
Homozygous Dominant Dominant
Heterozygous Dominant
Homozygous Recessive Recessive

2N


X
A a

2 Phenotype

AA 3 Genotype aa
Aa

A : dominant allele
a : recessive allele



X X
AA AA AA aa

AA AA AA AA Aa Aa Aa Aa
Genotype:
Genotype :
100% AA X 100% Aa
Phenotype :
Phenotype : AA Aa
100% dominant
100% Dominant

Genotype :
50% AA : 50% Aa
Phenotype :

AA Aa AA Aa 100% dominant


X X
Aa Aa Aa aa

AA Aa Aa aa Aa Aa aa aa
Genotype :
Genotype :

X
50% Aa : 50% aa
25% AA : 50% Aa :
25% aa Phenotype :
Phenotype : aa aa 50% Dominant :
50% recessive
75% Dominant :
25% recessive
Genotype :
100% aa
Phenotype :
100% recessive
© Dr. Shahreza, FPAI, UMT aa aa aa aa


Occurs when the dominant allele expresses itself more strongly than the
recessive allele but not strong enough to suppress the recessive allele in
the heterozygous genotype.

Dominant phenotype can be produced only when individual has 2 copies
of the dominant allele (Homozygous dominant, example : AA)

Heterozygous individuals will produced a phenotype that resembles but
not identical to the dominant phenotype

Each set of genotype produces its own phenotype :
3 Genotypes dan 3 Phenotypes

Genotype Phenotype
Heterozygous Heterozygous
>
2N


X
A a
3 Phenotype

AA Aa aa
3 Genotype

A : dominant allele
a : recessive allele


X X
AA AA AA aa

Genotype : Genotype :
100% AA
Phenotype : X 100% Aa
Phenotype :
100% Dominant
AA Aa
100% Semi-Dominant

Genotype
50% AA : 50% Aa
Phenotype :
50% Dominant : 50%
AA Aa AA Aa Semi-Dominant


X X
Aa Aa Aa aa

Genotype : Genotype :
25% AA : 50% Aa :
25% aa X 50% Aa : 50% aa
Phenotype :
Phenotype : aa aa
50% Semi-Dominant
25% Dominant : 50% : 50% recessive
Semi-Dominant :
25% recessive
Genotype :
100% aa
Phenotype :
100% recessive


Occurs when no allele is dominant over the other allele.

Both alleles contribute equally to the production of the phenotypes.

Heterozygous genotype (A a) produces a phenotype that is intermediate
between the 2 homozygous genotypes (A A or a a).

In additive gene action, 3 types of genotypes will produce 3 types of
phenotypes.

Genotype Phenotype
Heterozygous Heterozygous

2N


X
C C’

3 Phenotype

CC CC’ C’C’
3 Genotype



X X
AA AA AA aa

Genotype:
Genotype :
X
100% Aa
100 AA
Phenotype :
Phenotype : AA Aa 100% Co-Dominant
100% Dominant

Genotype :
50% AA : 50% Aa
Phenotype :

AA Aa AA Aa 50% Dominant :
© Dr. Shahreza, FPAI, UMT 50% Co-Dominant


X X
Aa Aa Aa aa

Genotype :
Genotype :

X
50% Aa : 50% aa
25% AA : 50% Aa :
25% aa Phenotype :
Phenotype : aa aa 50% Co-Dominant :
50% recessive
25% Dominant :
50% Co-Dominant :
25% recessive
Genotype :
100% aa
Phenotype :
100% recessive


X
A a

AA Aa aa

X
A a

AA Aa aa
X
C C’

CC
CC’ C’C’


Traits that can be measured
It is complex because it involves interaction of more than 2 genes.

Influenced by environmental factors.

Can be determined based on MEASUREMENT and DIMENSION

Interaction of
several genes

2N


Growth Rate
Fecundity
FCR (Feed Conversion Efficiency)
Dressout percentage
Tolerance to temperature, salinity
or low dissolve oxygen



In a population, variation of a trait forms a continuum rather than discrete
phenotypic classes.

Individual Length Weight
1 20.5 210.4
2 21.0 200.0
3 22.0 205.5
4 20.0 212.4
5 20.2 207.8
6 19.6 203.3
7 21.4 209.6

Example of a continuous data



Phenotypic Variance (VP) = VG + VE

Where :
VP = Phenotypic variance
VG = Genetic Variance
VE = Environmental variance



Genetic Variance (VG)
A component that breeders try to manipulate in a breeding
programme

Genetic variance is the sum of 3 components

ADDITIVE GENETIC VARIANCE

Superior
genetic traits
GENETIC VARIANCE

DOMINANCE EPISTATIC
GENETIC VARIANCE GENETIC VARIANCE


Genetic Variance

VG = VA + VD+ VI
Contribution of alleles Interaction between
towards the phenotypic pairs of alleles Interaction
Between Loci
production of a fish

Interaction
Among Loci
ADDITIVE DOMINANCE EPISTATIC
GENETIC VARIANCE (VA) GENETIC VARIANCE GENETIC VARIANCE
(VD) (VI)


Parent
Male Female
X

Contribution of alleles towards the Interaction between
phenotypic production of a fish pairs of alleles

ADDITIVE DOMINANCE
GENETIC VARIANCE (VA) Progeny
GENETIC VARIANCE (VD)


Notes kuliah1 aqu2203 sem_i 201213d

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