03 sex linked inheritance
- 2. SEX-LINKED TRAITS Male and female genotypes… XY XX
- 3. SEX-LINKED TRAITS How is sex determined? X Ya In this case, Y female child will result XX X Y X
- 4. SEX-LINKED TRAITS How is sex determined? X Ya In this case, Y male child will result XY X Y X
- 5. SEX-LINKED TRAITS The X-chromosome may contain alleles for the following: -Hemophilia -Colour blindness -Baldness -Duchenne muscular dystrophy These X-linked recessive “disorders” predominantly affect males.
- 6. SEX-LINKED TRAITS Females have two X chromosomes, so the X-linked recessive diseases will not affect them. XX XX H XX C XX B Phenotype: Normal Normal Normal Normal
- 7. SEX-LINKED TRAITS However, males only have one X-chromosome… XY X HY XC Y X BY
- 8. SEX-LINKED TRAITS However, males only have one X-chromosome… XY X HY XC Y X BY Phenotype: Normal Hemophiliac Colour blind Bald
- 9. SEX-LINKED TRAITS So how is baldness inherited? XXB XY X Y X XX XY X B XXB XBY F1 Genotypes: 25% XX, 25% XXB, 25% XY, 25% XBY F1 Phenotypes: 50% of males are bald. Females are “normal” (wild type)
- 10. SEX-LINKED TRAITS The female with the genotype XXB will not become bald, BUT she is a carrier She can pass the baldness allele to her XXB XXB offspring
- 11. SEX-LINKED TRAITS It is possible for women to be bald, too!
- 12. SEX-LINKED TRAITS How is this possible?! If the father is bald, and the mother is a carrier, then half of her children will become bald XXB XBY XB Y X XXB XY X B XBXB XB Y
- 13. SEX-LINKED TRAITS How is this possible?! If the father is bald, and the mother is a carrier, then half of her children will become bald It is very rare for a women to be bald. Why did I It’s not fair! have to be one of me Don’t get them?!! started… XXB XB XB XY XBY F1 Genotypes: 25% XXB, 25% XBXB, 25% XY, 25% XBY F1 Phenotypes: 50% of male and female offspring are bald
- 14. SEX-LINKED TRAITS So how is hemophilia inherited? In the same way as baldness, hemophilia is inherited usually because the mother is a carrier. Once again, usually male children are affected X Y X XX XY XX H XY X H XXH XH Y
- 15. SEX-LINKED TRAITS Sample question: If a hemophiliac man has children with a “normal” woman (who is NOT a carrier), a) What is the probability of having kids that will develop hemophilia b) What is the probability of female kids being carriers? XH Y X XXH XY a) _______________________ 0% chance of kids having X XXH XY hemophilia _________________________ 100% of females will be carriers b) ______________________________________________________