1. SEXRELATEDINHERITANCE Biology 3 Kent Kawashima

2. HOW ISSEX (gendeR)DETERMINED?

3. How is Sex Determined? XY ZW X0

5. In humans, males are XY (heterogametic) while females are XX (homogametic)

6. In humans, a single gene (SRY) on the Y chromosome acts as a signal to set the developmental pathway towards malenessXY

8. The ovum determines the sex of the offspring

9. In birds, males are ZZ (homogametic) while females are ZW(heterogametic)

10. The W chromosome is thought to be essentail for female sex determination or at least contain female-determining genes.ZW

12. The X0 system only has one sex chromosome – X

13. Males have only one X chromosome, (X0), females have two (XX)

14. The maternal gamete always contains an X chromosome. The sperm determines sex – containing either one X chromosome or no sex chromosomes at all.X0

15. SEXLIMITEDTraits

16. Sex-Limited Traits Autosomal, not found in the sex chromosomes Genes are carried by both males and females, but only one sex would ever express them Example: genes that influence how much milk a lactating mother produces when she’s nursing a baby Another example: cryptorchidism (undescended testicles)

17. SEXINFLUENCEDTraits

18. Sex-Influenced Traits Autosomal, not found in the sex chromosomes Genes are carried by both males and females, but there is a difference in the way the two sexes express them Example: pattern baldness in humans. The baldness allele behaves like a dominant allele in males, while in females it behaves like a recessive allele

19. SEXLINKEDTraits

20. Sex-Linked Traits Genes are found on the sex chromosomes Sex-linked traits are behave differently from autosomal traits when sex chromosomes are non-homologous May be dominant or recessive in nature Phenotype is dependent also on the presence of a complete gene pair or just one allele Example: Hemophilia (X-linked)