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