IB Biology 2015 Curriculum Genetics

1. 3.4 Inheritance
Essential Question: The inheritance of genes follows patterns.
http://upload.wikimedia.org/wikipedia/commons/1/11/Peas_in_pods_-_Studio.jpg

2. Understandings
Statement
3.4.U1
Mendel discovered the principles of inheritance with experiments in which large numbers
of pea plants were crossed.
3.4 U2 Gametes are haploid so contain only one allele of each gene.
3.4 U3
The two alleles of each gene separate into different haploid daughter nuclei during
meiosis.
3.4 U4
Fusion of gametes results in diploid zygotes with two alleles of each gene that may be the
same allele or different alleles.
3.4 U5
Dominant alleles mask the effects of recessive alleles but co-dominant alleles have joint
effects.
3.4 U6
Many genetic diseases in humans are due to recessive alleles of autosomal genes,
although some genetic diseases are due to dominant or co-dominant alleles.
3.4 U7
Some genetic diseases are sex-linked. The pattern of inheritance is different with sex-
linked genes due to their location on sex chromosomes. [Alleles carried on X
chromosomes should be shown as superscript letters on an upper case X, such as Xh.]
3.4 U8 Many genetic diseases have been identified in humans but most are very rare.
3.4 U9
Radiation and mutagenic chemicals increase the mutation rate and can cause genetic
diseases and cancer.

3. Applications and Skills
Statement Guidance
3.4 A1
Inheritance of ABO blood groups. [The expected notation for ABO
blood group alleles: O = i, A=IA, B = IB.]
3.4 A2
Red-green color blindness and hemophilia as examples of sex-
linked inheritance.
3.4 A3 Inheritance of cystic fibrosis and Huntington’s disease.
3.4 A4
Consequences of radiation after nuclear bombing of Hiroshima and
accident at Chernobyl.
3.4 S1
Construction of Punnett grids for predicting the outcomes of
monohybrid genetic crosses.
3.4 S2
Comparison of predicted and actual outcomes of genetic crosses
using real data. (Penny Lab)
3.4 S3
Analysis of pedigree charts to deduce the pattern of inheritance of
genetic diseases.

4. Gregor Mendel
• Austrian monk who
published results of garden
pea plants inheritance in
1865
• Used artificial pollination in
a series of experiments by
using a small brush to place
the pollen on the
reproductive parts of the
flowers
3.4 U.1 Mendel discovered the principles of inheritance with
experiments in which large numbers of pea plants were crossed.

5. Key terminology
1. Genotype – symbolic representation of pair of alleles possessed by
an organism, typically represented by two letters
• Ex: Bb, GG, tt
2. Phenotype – characteristics or traits of an organism
• Ex: five fingers on each hand, color blindness, type O blood
3. Dominant allele – an allele that has the same effect on the
phenotype whether it is paired with the same allele or a different
one; always expressed in phenotype
• Ex: Aa give dominant trait A because the a allele is masked; the
a allele is not transcribed and translated during protein
synthesis
3.4 U.1 Mendel discovered the principles of inheritance with
experiments in which large numbers of pea plants were crossed.

6. 4. Recessive allele – an allele that has an effect on the
phenotype only when present in the homozygous state
• Ex: aa gives rise to the recessive trait because no
dominant allele is there to mask it
5. Codominant allele – pairs of alleles that both affect the
phenotype when present in a heterozygote
• Ex: parent with curly hair and parent with straight
hair can have children with different degrees of
curliness as both alleles influence hair condition
when both are present in the genotype
6. Locus – particular position on homologous chromosomes
of a gene
3.4 U.1 Mendel discovered the principles of
inheritance with experiments in which large numbers
of pea plants were crossed.

7. 7. Homozygous – having two identical alleles of a gene
Ex: AA is a genotype which is homozygous dominant
whereas aa is the genotype which is homozygous
recessive
8. Heterozygous – having two different alleles of a gene
Ex: Aa is a heterozygous genotype
9. Carrier – an individual who has a recessive allele of a
gene that does not have an effect on their
phenotype
3.4 U.1 Mendel discovered the principles of
inheritance with experiments in which large numbers
of pea plants were crossed.

8. 10. Test cross – testing a suspected heterozygote plant
or animal by crossing it with a known homozygous
recessive (aa). Since a recessive allele can be
masked, it is often impossible to tell if an organism
is AA or Aa until they produce offspring which
have the recessive trait.
3.4 U.1 Mendel discovered the principles of
inheritance with experiments in which large numbers
of pea plants were crossed.

9. 3.4 U.1 Mendel discovered the principles of inheritance with
experiments in which large numbers of pea plants were crossed.

10. 3.4 U.1 Mendel discovered the principles of inheritance with
experiments in which large numbers of pea plants were
crossed.

11. Mendel’s Law of Segregation
Four parts
• Alternative versions of genes account for variations in inherited
characteristics.
• For each characteristic, an organism inherits two alleles, one from
each parent.
• If the two alleles differ, then one, the allele that encodes the
dominant trait, is fully expressed in the organism's appearance; the
other, the allele encoding the recessive trait, has no noticeable effect
on the organism's appearance.
• The two alleles for each characteristic segregate during gamete
production
3.4 S.1 Construction of Punnett grids for predicting the outcomes of
monohybrid genetic crosses.

12. Principle of Segregation: Each Parent or Gamete
Contributes One Allele to Offspring
3.4 S.1 Construction of Punnett grids for predicting the outcomes of
monohybrid genetic crosses.

13. Punnet Square:
Used to determine the outcome of a cross between two individuals.
In the example we have two parents that are heterozygous
dominant for a trait
Offspring:
Genotype: 1/4 PP, 1/2 Pp, and 1/4 pp
Phenotype: 3/4 Purple and 1/4 white
3.4 S.1 Construction of Punnett grids for predicting the outcomes of
monohybrid genetic crosses.

14. 3.4 U.2 Gametes are haploid so contain only one allele of
each gene.
• Gametes are sex cell.
• Sex cells contain one chromosome
of each type, as an example Humans
have 23 types.
• Parents pass information in
the form of genes in gametes (sex cell)
• These cell will fuse together with the
cell of the opposite sex to create a
zygote.

15. Meiosis = reduction
division
• Cells divide twice
• Result: 4 daughter
cells, each with half
as many
chromosomes as
parent cell
3.4 U.3 The two alleles of each gene separate into different
haploid daughter nuclei during meiosis.

16. Life cycle: reproductive history of organism, from
conception  production of own offspring
• Fertilization and meiosis alternate in sexual life cycles
• Meiosis: cell division that reduces # of chromosomes (2n 
n), creates gametes
• Fertilization: combine gametes (sperm + egg)
– Fertilized egg = zygote (2n)
• Zygote divides by mitosis to make multicellular diploid
organism
3.4 U.4 Fusion of gametes results in diploid zygotes with two alleles of
each gene that may be the same allele or different alleles.
.

17. Human Life Cycle
3.4 U.4 Fusion of gametes results in diploid zygotes with two alleles of
each gene that may be the same allele or different alleles.
.

18. 3.4 U.4 Fusion of gametes results in diploid zygotes with two alleles of
each gene that may be the same allele or different alleles.
.

19. 3.4 U.5 Dominant alleles mask the effects of recessive alleles but co-
dominant alleles have joint effects.
.
http://gestblog.scientopia.org/wp-content/uploads/sites/35/2012/07/10-04.gif

20. Problems with predictions
I. Codominance
II. Multiple alleles
III. Sex linked genes

21. http://image.slidesharecdn.com/incompletecodominancemultiplealleles-120127095123-phpapp02/95/incomplete-codominance-multiplealleles-7-728.jpg
3.4 U.6 Many genetic diseases in humans are due to recessive alleles of
autosomal genes, although some genetic diseases are due to dominant
or co-dominant alleles

22. 3.4 U.6 Many genetic diseases in humans are due to recessive alleles of
autosomal genes, although some genetic diseases are due to dominant
or co-dominant alleles
Inheritance characterized by full expression of both alleles in
the heterozygote.
Seen in:
• Roan Cattle
• Tay Sacs disease
• Blood Types
You have a brown Bull and a
white Cow. You cross them and
get a mix of the two colors.
BB = Brown Bull/Cow
WW = white Bull/Cow
BW = Mixture of the two colors

23. 3.4 U.6 Many genetic diseases in humans are due to recessive alleles of
autosomal genes, although some genetic diseases are due to dominant
or co-dominant alleles
https://jeanurquharthighlandsandislandsmsp.files.wordpress.com/2014/06/cavans-bourbon-orkney-by-robert_scarth-on-flickr.jpg

24. Sickle Cell Anemia: (example of a codomainant gene
mutation and its consequences through protein synthesis)
The Genetics of Sickle Cell Anemia
•HBA HBA Suceptible to malaria with anemia
• HBA HBs Increase resistance to malaria with mild anemia
• HBs HBs Sickle cell shaped cell Suceptible to malaria with
severe anemia
3.4 U.6 Many genetic diseases in humans are due to recessive alleles of
autosomal genes, although some genetic diseases are due to dominant
or co-dominant alleles

25. 3.4 U.6 Many genetic diseases in humans are due to recessive alleles of
autosomal genes, although some genetic diseases are due to dominant
or co-dominant alleles

26. 3.4 U.6 Many genetic diseases in humans are due to recessive alleles of
autosomal genes, although some genetic diseases are due to dominant
or co-dominant alleles

27. 3.4 U.6 Many genetic diseases in humans are due to recessive alleles of
autosomal genes, although some genetic diseases are due to dominant
or co-dominant alleles

28. 3.4 U.6 Many genetic diseases in humans are due to recessive alleles of
autosomal genes, although some genetic diseases are due to dominant
or co-dominant alleles

29. 3.4 U.6 Many genetic diseases in humans are due to recessive alleles of
autosomal genes, although some genetic diseases are due to dominant
or co-dominant alleles

30. 3.4 A.1 Inheritance of ABO blood groups. [The expected notation for
ABO blood group alleles: O = i, A=IA, B = IB.]
There are 4: A, B, AB and O
A & B refer to 2 genetically
inherited A and B antigens on
the surface of red blood cells.
IA – codes for A
IB – codes for B
i - codes for no antigen = type
O blood

31. Multiple Alleles: ABO Blood Groups
Blood type O: Universal donor. Blood type AB: Universal acceptor
3.4 A.1 Inheritance of ABO blood groups. [The expected notation for
ABO blood group alleles: O = i, A=IA, B = IB.]

32. 3.4 A.1 Inheritance of ABO blood groups. [The expected notation for
ABO blood group alleles: O = i, A=IA, B = IB.]

33. Sex Chromosomes
3.4 U.7 Some genetic diseases are sex-linked. The pattern of inheritance
is different with sex-linked genes due to their location on sex
chromosomes. [Alleles carried on X chromosomes should be shown as
superscript letters on an upper case X, such as Xh.]
• The X chromosome in humans
spans more than 153 million base
pairs (the building material
of DNA). It represents about 2000
out of 20,000 - 25,000 genes.
• The Y chromosome containing
78genes, out of the estimated
20,000 to 25,000 total genes in the
human genome. Genetic disorders
that are due to mutations in genes
on the X chromosome are
described as X linked.

34. 3.4 U.7 Some genetic diseases are sex-linked. The pattern of inheritance
is different with sex-linked genes due to their location on sex
chromosomes. [Alleles carried on X chromosomes should be shown as
superscript letters on an upper case X, such as Xh.]
Male sex chromosomes
• There are non-homologous
region males in which there
is only one allele per gene
and that is inherited from
the female on the X-
chromosome
• In the homologous region
the male inherited two
copies of an allele per gene.

35. Female sex chromosomes
• All regions of the X
chromosome are
homologous.
• There are two alleles per
gene as with all other genes
on all other chromosomes
This difference in x and y chromosomes plays a large role in
determining rates of genetic inherited defects
3.4 U.7 Some genetic diseases are sex-linked. The pattern of inheritance
is different with sex-linked genes due to their location on sex
chromosomes. [Alleles carried on X chromosomes should be shown as
superscript letters on an upper case X, such as Xh.]

36. Sex Linkage Alleles on the non-homologous region of the
X chromosome are more common in females than in
males
• A gene with two alleles where one is dominant and one is recessive.
• Female has three possible genotypes and one is the homozygous
recessive.
• In a population the chance of being homozygous recessive is 33.3 %.
• Males have two possible genotypes.
• There is a 50% chance of the homozygous recessive condition in the
population.
• In sex linked conditions the recessive condition is more common in
males than females.
3.4 U.7 Some genetic diseases are sex-linked. The pattern of inheritance
is different with sex-linked genes due to their location on sex
chromosomes. [Alleles carried on X chromosomes should be shown as
superscript letters on an upper case X, such as Xh.]

37. 3.4 U.7 Some genetic diseases are sex-linked. The pattern of inheritance
is different with sex-linked genes due to their location on sex
chromosomes. [Alleles carried on X chromosomes should be shown as
superscript letters on an upper case X, such as Xh.]

38. Female carriers of sex linked alleles
• Female heterozygote's for sex linked alleles e.g. Hemophilia
XHXh or Color Blindness XBXb are carriers of the allele.
• They are unaffected by the condition.
• They do pass on the allele which may result in a
homozygous female or a male with the sex linked recessive
allele.
3.4 A.2 Red-green color blindness and hemophilia as
examples of sex-linked inheritance.

39. Sex Linkage Examples:
Hemophilia
• Hemophilia is an example of a
sex linkage condition.
• The hemophilia allele is
recessive to the normal allele.
• The gene is located on the non-
homologous region of the X
chromosome.
• The disease is associated with
an inability to produce a clotting
factor in blood.
• Internal bleeding takes longer to
stop.
3.4 A.2 Red-green color blindness and hemophilia as
examples of sex-linked inheritance.
http://blog.nz-online.de/lieb/wp-content/uploads/sites/8/2010/07/blut.jpg

40. • The
homozygous
genotype(*) in
females has a
high mortality.
• The genotype
XnY in males
has a high
mortality.
3.4 A.2 Red-green color blindness and hemophilia as
examples of sex-linked inheritance.
Hemophilia
Hemophilia

41. • Red Green Color Blindness is an
example of a sex linked
condition.
• Red Green Color blindness is a
recessive condition.
• The color blind allele is recessive
to the normal allele.
• Female homozygous recessives
XbXb are color blind.
• Males with the genotype XbY are
color blind.
• Notice that in a population the
probability of having a Red Green
color blind genotype in males is
higher.
3.4 A.2 Red-green color blindness and hemophilia as
examples of sex-linked inheritance.
http://en.wikipedia.org/wiki/Color_blindness#/media/File:Ishihara_9.png
Above is a color test
plate.[The numeral "74"
should be clearly visible to
viewers with normal color
vision.

42. 3.4 A.2 Red-green color blindness and hemophilia as
examples of sex-linked inheritance.
http://upload.wikimedia.org/wikipedia/commons/a/a3/XlinkRecessive.jpg
Normal color vision
Red/green color blindness

43. Pedigree Chart
• Another way to visualize a
monohybrid crosses or
determining a genotype is by
using a pedigree chart
• Knowing the phenotype of
individuals in a family will
sometimes allow genotypes to
be determined.
• In genetic counseling this
enables probabilities to be
determined for the inheritance
of characteristics in children.
3.4 S.3 Analysis of pedigree charts to deduce the pattern of
inheritance of genetic diseases.

44. Pedigree Chart
• White circle : Normal
female
• White Square: Normal
male
• Black Circle: affected
female
• Black square: affected male
• (1) and (2)..Normal Parents
• (3) affected female
• (4),(5) and (6) normal
3.4 S.3 Analysis of pedigree charts to deduce the pattern of
inheritance of genetic diseases.

45. 3.4 S.3 Analysis of pedigree charts to deduce the pattern of
inheritance of genetic diseases.

46. 3.4 S.3 Analysis of pedigree charts to deduce the pattern of
inheritance of genetic diseases.

47. 1. Phenylketonuria (Pku)
• Using the allele key provided
state the genotype of parents
1 and 2?
• Give the genotype and
phenotype of individual 5 ?
• Is it possible that the
condition is sex linked ?
• What is the genotype and
phenotype of individuals 7
and 8?
• Which two individuals have
the incorrect pedigree
3.4 S.3 Analysis of pedigree charts to deduce the pattern of
inheritance of genetic diseases.

48. 2. Muscular Dystrophy
• What type of genetic disease
is muscular dystrophy?
• Give the genotype and
phenotype of 1?
• Give the genotype and
phenotype of 2?
• Give the genotype and
phenotype of 8 ?
• Give the genotype and
phenotype of 5 and 6 ?
3.4 S.3 Analysis of pedigree charts to deduce the pattern of
inheritance of genetic diseases.

49. Cystic fibrosis (CF) Non Sex link recessive genetic trait found
on Chromosome 7
Example: Cross
The couple below are heterozygous for CF
3.4 A.3 Inheritance of cystic fibrosis and Huntington’s disease.
http://www.bbc.co.uk/staticarchive/088e5fc50b3c51cfb49ebc4b6eaf203b18b93bbc.gif

50. Huntington’s Disease Non Sex link dominant genetic trait
The couple two couples below are examples
• Couple 1: 1 heterozygous (has trait) with 1 homozygous (without the
trait)
• Couple 2: Both parents are heterozygous with Huntington's
3.4 A.3 Inheritance of cystic fibrosis and Huntington’s disease.
http://vanhornhuntingtonsdisease.weebly.com/uploads/1/3/7/4/13740905/4993818.jpg?1347964948
Couple 1 Couple 2

51. 3.4 U.8 Many genetic diseases have been identified in humans but most
are very rare.
• Medical research has identified
over 4,000 genetic diseases,
however many individuals do
not suffer from one.
• Most genetic diseases are
caused by rare recessive
alleles. Making the chance of
inheritance very small.
• Genetic sequencing of the
human genome current
estimates are that there
maybe as little as 75-200
genes out of over 20,000
genes in the genome that
contain these traits.

52. 3.4 U.9 Radiation and mutagenic chemicals increase
the mutation rate and can cause genetic diseases and
cancer.
A mutagen is a physical
(radiation) or chemical
agent like Nitrosamines,
found in tobacco. These
mutagens change the genetic
material, usually DNA, of
an organism and increases
the frequency
of mutations above the
natural background level.
Many mutations
cause cancer, mutagens are
therefore also likely to
be carcinogens.

53. • Radiation-induced cancers do not appear until at least 10 years after exposure (for
tumors) or 2 years after exposure (for leukemia).
• The risk of cancer after exposure can extend beyond this latent period for the rest
of a person’s life for tumors or about 30 years for leukemia.
• Risk is calculations are based on:
– The type of radiation.
• Each type of radiation is different and affects tissues differently.
– The energy that it leaves in the body.
• More energy means a higher probability of an effect.
– Where in the body the energy remains.
• Radiation exposure to a non-sensitive area of the body (i.e., wrist) really
has no actual effect. Radiation exposure to a sensitive area of the body (i.e.,
blood-forming organs) can have an effect if the amount of energy left is
high enough.
3.4 U.9 Radiation and mutagenic chemicals increase the mutation
rate and can cause genetic diseases and cancer.

54. • Indirect damage
– Water molecule is ionized, breaks apart,
and forms OH free radical.
– OH free radical contains an unpaired
electron in the outer shell and is highly
reactive: Reacts with DNA.
– 75 percent of radiation-caused DNA
damage is due to OH free radical.
• Direct damage
– DNA molecule is struck by radiation,
ionized, resulting in damage.
3.4 U.9 Radiation and mutagenic chemicals increase the mutation
rate and can cause genetic diseases and cancer.

55. Chromosome Damage
Formation of a ring and fragments followed
by replication of chromosomes.
3.4 U.9 Radiation and mutagenic chemicals increase the mutation
rate and can cause genetic diseases and cancer.

56. Chromosome Damage
Interchange between two chromosomes
forms a chromosome with two centromeres
and fragment, followed by replication.
3.4 U.9 Radiation and mutagenic chemicals increase
the mutation rate and can cause genetic diseases and
cancer.

57. Commonly Encountered Radiation Doses
Effective Dose Radiation Source
<= 0.01 rem annual dose living at nuclear power plant panoramic, or full-mouth dental
x rays; skull or chest x ray
<=0.1 rem single spine x ray; abdominal or pelvic x ray; hip x ray; mammogram
<=0.5 rem kidney series of x rays; most barium-related x rays; head CT; any spine x-ray
series; annual natural background radiation dose; most nuclear
medicine brain, liver, kidney, bone, or lung scans
<=1.0 rem barium enema (x rays of the large intestine); chest, abdomen, or pelvic CT
<=5.0 rem cardiac catheterization (heart x rays); coronary angiogram (heart x rays);
other heart x-ray studies; most nuclear medicine heart scans
CT = computerized tomography; a specialized x-ray exam.
3.4 A.4 Consequences of radiation after nuclear bombing of Hiroshima
and accident at Chernobyl.

58. Radiation Doses and Expected Effects (cont.)
General radiation doses to the entire body and expected effects:
• 100-200 rem received in a short time will cause nausea and fatigue.
• 100-200 rem received over a long period will increase a person’s chances of getting cancer.
• 200-300 rem received in a short time will cause nausea and vomiting within 24-48 hours.
Medical attention should be sought.
• 300-500 rem received in a short time will cause nausea, vomiting, and diarrhea within hours.
Loss of hair and appetite occurs within a week. Medical attention must be sought for
survival; half of the people exposed to radiation at this high level will die if they receive no
medical attention.
• 500-1,200 rem in a short time will likely lead to death within a few days.
• Greater than 10,000 rem in a short time will lead to death within a few hours.
3.4 A.4 Consequences of radiation after nuclear bombing of Hiroshima
and accident at Chernobyl.

59. 3.4 A.4 Consequences of radiation after nuclear bombing of Hiroshima
and accident at Chernobyl.
http://inapcache.boston.com/universal/site_graphics/blogs/bigpicture/hiroshima_08_05/h17_04.jpg

60. 3.4 A.4 Consequences of radiation after nuclear bombing of Hiroshima
and accident at Chernobyl.
http://www.nucleardarkness.org/include/nucleardarkness/images/cityonfire/hiroshima_after_02_full.jpg

61. 3.4 A.4 Consequences of radiation after nuclear bombing of Hiroshima
and accident at Chernobyl.
http://www.zap-actu.fr/wp-content/uploads/2013/11/pripyat-une-des-villes-fantomes-pres-de-tchernobyl-01.jpg

62. 3.4 A.4 Consequences of radiation after nuclear bombing of Hiroshima
and accident at Chernobyl.