1. Genetics Quick Review of Grade 11 Sex Linked Traits
Sex Influenced Traits
Polygenic Traits
Epistatic Genes

2. How many chromosomes do humans have?
46…or 23 homologous pairs
23 from your mother and 23 from your father
Pairs1 through 22 = autosomal chromosomes
Which chromosomes determine if you’re a girl or boy?

3. Two Types of Chromosomes
Two Types of Cells
Somatic Cells – All body cells,
diploid (2n)
Sex Cells – Gametes, haploid (n)
Two Types of Chromosomes
Autosomal – All body cells
Sex Chromosomes – X and Y

4. The Sex chromosomes
Its all up to
Dad….
If you get a X
you’re a girl

5. The Sex chromosomes
But... If you get a
Y you’re a boy

6. Punnett Squares X X X XX XX Y XY XY

7. Phenotype Genotype Allele Homozygous Heterozygous
Expressed trait (physical appearance)
Phenotype
The set of genes that an organism possesses
Genotype
Allele
Different forms of the same gene
When two alleles are identical Ex. DD
Homozygous
When the two alleles are different Ex. Dd
Heterozygous

8. Dominant
Allele which controls the characteristic whenever it is present.
BB or Bb
recessive
Allele whose characteristics only show up when it is present on both chromosomes bb

9. Genetics Quick Review of Grade 11 Sex Linked Traits
Sex Influenced Traits
Polygenic Traits
Epistatic Genes

10. Sex Linked Traits
Sex-linked traits are traits that are controlled by genes on the sex chromosomes
Examples:
Colour Blindness
Hemophilia

11. 3 Different Forms of Sex Linked Inheritance
X-linked recessive inheritance
X-linked dominant inheritance
Y-linked inheritance

12. Sex Linked Inheritance Notation
X-linked recessive alleles are represented by a X with a superscript of either:
+ (dominant) or
– (recessive)

13. Genotypes of Sex Linked Inheritance
What are the possible genotypes of a sex linked inheritance for a female?
X+X+ X+X - X -X -
What are the possible genotypes for sex linked inheritance for a male?
X+Y X - Y

14. 1. X-linked Recessive Inheritance
X-linked recessive traits are traits resulting from a recessive allele on the X chromosome

15. Why do X-linked recessive traits show up more often in men than women?

16. Are YOU Colorblind? Normal Color Vision: A: 29, B: 45, C: --, D: 26
Red-Green Color-Blind: A: 70, B: --, C: 5, D: -- 3.
Red Color-blind: A: 70, B: --, C: 5, D: 6 4.
Green Color-Blind: A: 70, B: --, C: 5, D: 2

17. X-linked Recessive Inheritance
Example #1: Colorblindness
The allele that controls colorblindness is found on the X chromosome and is recessive
What genotype must a female have to be diagnosed as colorblind?
X -X-

18. Possible Colorblindness Phenotypes
X+X+
Female with Normal Vision
X+X –
Female with Normal Vision (Carrier)
X -X –
Colour Blind Female
X+Y –
Male with Normal Vision
X – Y
Colour Blind Male

19. Let’s try a cross: X+X– • X+Y
Phenotypes
Females:
Males:

20. Let’s try a cross: X+X– • X-Y
Phenotypes
Females:
Males:

21. Let’s try a cross: X+X+ • X-Y
Phenotypes
Females:
Males:

22. Let’s try a cross: X-X- • X+Y
Phenotypes
Females:
Males:

23. Try these questions on your own:
A woman who is heterozygous (a carrier) for colorblindness marries a man with normal vision. What will be the possible phenotype ratio of their children?
What is the probability that the sons of a homozygous recessive mother would be colour blind?
*Remember to represent colorblindness with a “-”

24. More examples of X-linked Recessive Inheritance
Example #2: Hemophilia
Hemophilia is a serious ailment in which the blood lacks a clotting factor, and therefore when an individual is injured, they cannot stop bleeding
About 1 in 4,000 males are born with disorder, much lower incidence in females

25. Hemophilia Pedigree

26. Just to make sure you got it! ;)
A woman who is heterozygous for hemophilia marries a normal man:
a. What are the genotypes of the parents?
b. Make a Punnett square for the cross
c. What is the probability that a male offspring will have hemophilia?
d. What is the probability of having a hemophiliac female offspring?

27. 2. X-linked Dominant Inheritance
X-linked dominant traits are traits that result from the presence of a dominant allele on the X chromosome
Unlike X-linked recessive traits, females and males both require only ONE dominant allele in order to express the trait

28. X-linked Dominant Inheritance
Example #1: Faulty Tooth Enamel and Dental Discoloration
Individuals who have an X chromosome that carries a dominant allele for this trait will have dental discoloration.

29. Possible Dental Disorder Phenotypes
X+X+
Female with Dental Discoloration
X+X –
X -X –
Normal Female
X+Y
Male with Dental Discoloration
X – Y
Normal Male

30. Let’s think about it...
Would a heterozygous woman for dental discoloration display the trait?
Yes, because dental discoloration is a X-linked dominant trait, so only one dominant allele is needed to express the trait
What percentage of the children from a heterozygous mother and an affected father would have dental discoloration?

31. 3. Y-linked Inheritance
Y-linked traits are controlled by alleles on the Y chromosome
Another word for Y-linked traits is holandric traits (“wholly male”)
Are females affected by Y-linked traits?
Do the words homozygous or heterozygous apply to Y-linked traits?

32. What do these 2 have in common?
Example of Y-Linked Inheritance – HAIRY EARS!
Anthony Victor (India) has hair sprouting from the centre of his outer ears (middle of the pinna) that measures 18.1 cm (7.12 in) at its longest point.

33. All of the sons of an affected male will display this Y-linked trait

34. Last Sex-linked Trait Example
Eye color in fruit flies (Drosophilia melanogaster )
Eye color is controlled by the X chromosome
Red eyes are dominant to white
White eyes are most common in males
Females only display white eyes if they are homozygous recessive for the trait

35. Fruit Flies Continued What type of X-linked inheritance is this?
Try your new knowledge out on the handout you are about to receive!
X-linked recessive Inheritance because the males show the trait more often that the females. Also, the females must have two X chromosomes, both of which carry the recessive alleles for white eye color in order to have white eyes!

36. Genetics Quick Review of Grade 11 Sex Linked Traits
Sex Influenced Traits
Polygenic Traits
Epistatic Genes

37. What’s the Difference?
Sex-Linked Traits: alleles on sex chromosomes
Sex-Influenced Traits: alleles on autosomal (1-22) chromosomes

38. Sex-Influenced Traits
Controlled by a pair of alleles on autosomal chromosomes but its phenotypic expression is influenced by the presence of certain hormones
Can be seen in BOTH sexes, but will vary in frequency between the sexes or in the degree of the phenotypic expression
Estrogen, Progesterone, Testosterone, etc.

39. Sex-Influenced Traits
Example #1: Pattern Baldness
Pattern Baldness can occur in both males and females, but is much more common in males….
Why?
Because the pattern baldness trait is influenced by the hormone testosterone

40. The combination of alleles for pattern baldness will lead to different phenotypic expressions depending on the sex of the individual
Unlike male-pattern baldness, female-pattern baldness is an over-all thinning which maintains the normal hairline

41. Possible Pattern Baldness Phenotypes
Example: Let B represent the non-bald allele BB Non-bald in both sexes bb Bald in both sexes Bb Bald in men Non-bald in females
The “B” allele acts as a dominant allele in the heterozygous genotype in females, but acts as a recessive allele in the heterozygous genotype of the male

42. Let’s check your understanding…
What would Locke’s genotype be?
Bb or bb
What about his ‘we’ll-assume-for-the-sake-of-this-example’ balding mother? bb

43. To solve these questions, we can use simple Monohybrid Crosses
Then able to make conclusions regarding phenotypes based on the sex of the individual

44. Now you try…
A heterozygous balding male reproduces with a heterozygous normal female.
Do the cross and determine the phenotypic ratios for males and females

45. Let’s make it personal…
What is the probability that YOU will be bald if your father is homozygous and balding, and your mother is homozygous and not balding?

46. If only it were that simple!
Hair is controlled by many different factors including several alleles and environmental factors (polygenic traits)
So, we cannot fully explain pattern baldness using sex-influenced inheritance.
It is not easy to explain the diversity found in different ages of onset, as well as severity of baldness.

47. More Sex-Influenced Trait Examples
A male homozygous for clubfoot reproduces with a normal homozygous female.
What are the genotypes and phenotypes of their children if testosterone alters the phenotypic expression of the trait in the heterozygous expression?
Let F represent normal feet
Let f represent clubfoot.

48. More Sex-Influenced Trait Examples
Two heterozygous individuals get married and have lots of children. The father suffers with a painful condition called gout.
What are the parent’s genotypes?
What are the genotypes and phenotypes of the children?
Let G represent no gout
Let g represent gout

49. More Sex-Influenced Trait Examples
Rheumatoid arthritis occurs more often in females than males due to the presence of estrogen. A heterozygous woman marries a heterozygous male
RR would cause the condition in both sexes A homozygous recessive, rr, genotype would prevent the disorder in both sexes

50. More Sex-Influenced Trait Examples
Singing voice!
The genotype that causes males to have a high tenor voice causes females to have a deep contralto voice. The genotype that causes males to have deep bass voices is the same genotype that causes females to have high soprano voices!
Design a question involving the Sex-Influenced trait of singing voice

51. Genetics Quick Review of Grade 11 Sex Linked Traits
Sex Influenced Traits
Polygenic Traits
Epistatic Genes

52. Polygenic Traits
Those traits that are determined by the combined effect of 2 or more pairs of alleles
Each pair of alleles adds something to the resulting phenotype
Other names for polygenic traits are: multi-factorial traits or quantitative traits

53. Polygenic Traits
Because so many alleles contribute to the final phenotype, a variety of phenotypes can occur!
For example, height is a polygenic trait

54. To solve polygenetic trait questions that are only controlled by 2 pairs of alleles, we can use a Dihybrid Cross (Punnett Square)

55. Polygenic Traits Example #1: Pepper Colour
Gene 1: R = red r = yellow Gene 2: Y = absence of chlorophyll (no green) y = presence of chlorophyll (green)

56. Possible Pepper Colour Phenotypes
R -Y – Red (Red/No Chlorophyll) R – yy Brown/Orange (Red/Chlorophyll) rrY – Yellow (Yellow/No Chlorophyll) rr/yy Green (Yellow/Chlorophyll)

57. Pepper Colour Questions
Try crossing a brown pepper (RRyy) with a yellow pepper (rrYY).
Which trait will your offspring (F1 generation) produce?
What traits are produced when you cross two of the peppers found in the F1 generation?

59. Comb shape is controlled
Polygenic Traits
Example #2: Chicken Combs
Comb shape is controlled
by 2 genes found on 2
different pairs of
chromosomes
Gene 1: R
Gene 2: P

60. Possible Chicken Comb Phenotypes
R – pp Rose Combs R -P – Walnut Combs rrP – Pea Combs rr/pp Single Combs

61. Practice Makes Perfect!
Indicate the phenotypes of the parents and give the genotypic and phenotypic ratios of their offspring for the following crosses:
rrPP x RRpp
RrPp x RrPp
**Refer to your phenotype chart for chickens

62. Polygenic Traits Example #3: Hair Colour Hair colour is controlled by
alleles on chromosomes 3,
6, 10 & 18
The most dominant alleles
that appear in the genotype,
the darker the hair

63. Polygenics Plant Height Problem
The height of plants is controlled by 4 pairs of alleles Alleles A, B, and C contribute 3 cm to the plant's height. Alleles that are recessive do not contribute to the height Gene L is always found in a homozygous dominant condition and always contributes 40 cm to the height.
What would be the height of a plant with the genotype AABBCCLL?
What would be the height of a plant with a genotype aabbccLL?
What would be the height of the offspring produced from a cross between the plants in a) and b)?
What would be the heights of the offspring produced from a cross between AaBbCcLL and AaBbCcLL? (now there is a challenge!)

64. Genetics Quick Review of Grade 11 Sex Linked Traits
Sex Influenced Traits
Polygenic Traits
Epistatic Genes

65. Epistasis
Epistasis is a form of a gene interaction in which one pair of alleles (gene) masks the phenotypic expression of another
There are no new phenotypes produced by this interaction

66. Epistatic versus Hypostatic
Epistatic: the alleles that mask the effect
Hypostatic: the alleles whose effect is being masked

67. Epistatic trait questions can be solved like polygenic trait questions with a Dihybrid Cross The difference is that there is now one pair of alleles masking the other