1. Sex Chromosomes

2. Sex Chromosomes

3. X-linked Traits Possible genotypes X+Y  Hemizygous wild type male
XmY Hemizygous mutant male
X+X+  Homozyogus wild female
X+Xm  Heterozygous female carrier
XmXm  Homozygous mutant female

4. X-linked Recessive Inheritance
Always expressed in hemizygous males
Female homozygotes show the trait but female heterozygotes do not
Affected males: Inherited from affected or heterozygous mother
Affected females: affected fathers and affected or heterozygous mothers

6. X-linked Dominant Inheritance
Expressed with one copy
Males are often more severely affected
Typically associated with miscarriage or lethality in males
Passed from father to all his daughters but none of his sons

7. X-linked Dominant Inheritance: Congenital Generalized Hypertrichosis
Figure 6.10

8. Sex-limited traits
A trait that affects a structure or function of the body that is present in only one of the sexes.
May be X-linked or autosomal
Example: A gene affecting milk production will not have an effect in males. However, males can carry and pass on the trait.
Why do men have nipples anyway???

9. Sex-influenced traits
An allele is dominant in one sex but recessive in the other sex.
May be X-linked or autosomal
Due to hormonal interactions
Men have testosterone
Women have estrogen

10. X-inactivation
Females “turn off” one of their X chromosomes in each cell
In order to be more equal to males who only have one X chromosome
The X chromosome turned off in each cell is random

11. X Chromosome Inactivation

12. Fur Color in Tortoiseshell Cats
Orange fur
Black fur

13. Manifesting Heterozygote
A carrier of an X-linked trait who expresses the phenotype
If a female is heterozygous for a recessive trait, the dominant allele will usually mask the recessive allele…
Unless the dominant allele is on the X chromosome that was inactivated
Some cells will express the trait and others will not, depending on which X chromosome is inactivated

14. Multifactorial Traits
Genes and the Environment

15. Polygenic Traits A trait is influenced by more than one gene
May be multifactorial (influenced by environment)

16. Polygenic Traits are Continuously Varying
Each gene in the polygenic trait contributes to the phenotype to a varying degree
Example: Height
Polygenic (influenced by multiple genes)
Continuous

17. Pure Polygenic Trait -Eye Color
Figure 7.3
The number of human eye color genes is unknown
Analysis will probably reveal many genes
Mice have more than 60 eye color genes

18. Analyzing Multifactorial Traits
Difficult, requires multiple techniques
Use human genome sequences, population, and family studies
The frequency in a specific population = Empiric risk
The amount of inheritance due to genes = Heritability

19. Separating Genes and Environment
Dizygotic twins: Shared environment
and 50% of genes
Monozygotic twins: Identical genotype, and
shared environment
Twins raised apart: Shared genotype but
not environment
Adopted individuals: Shared environment
but not genes

20. Concordance
The percentage of pairs in which both twins express the trait
Used to determine heritability
Assumes both types of twins share similar environments
MZ twins often share more similar environments

21. Review
Mitochondrial

22. X-linked Recessive