Understanding Hemophilia Inheritance
Hemophilia is a sex-linked recessive disorder, typically associated with the X chromosome. Let's denote:
- \( X^H \) as the normal allele (dominant)
- \( X^h \) as the hemophilia allele (recessive)
F1 Generation
Parents:
1. Mother: Carrier of hemophilia (heterozygous) \( X^H X^h \)
2. Father: Normal \( X^H Y \)
Offspring:
- Son: Hemophiliac \( X^h Y \)
- Daughter: Normal \( X^H X^h \) (Carrier, like her mother)
F2 Generation
Daughter: \( X^H X^h \) (Carrier)
Son-in-law: \( X^H Y \) (Normal)
Offspring:
- Sons:
- 50% Normal: \( X^H Y \)
- 50% Hemophiliac: \( X^h Y \)
- Daughters:
- 50% Normal (Carrier): \( X^H X^h \)
- 50% Normal (Non-carrier): \( X^H X^H \)
Given that their grandson is hemophiliac, his genotype must be \( X^h Y \).
Conclusion
1. Genotype of F1 Generation:
- Mother: \( X^H X^h \) (Carrier)
- Father: \( X^H Y \) (Normal)
- Hemophiliac Son: \( X^h Y \)
- Normal Daughter: \( X^H X^h \) (Carrier)
2. Genotype of F2 Generation:
- Carrier Daughter: \( X^H X^h \)
- Normal Son-in-law: \( X^H Y \)
- Grandson (Hemophiliac): \( X^h Y \)
- Other possible offspring:
- Normal Sons: \( X^H Y \)
- Carrier Daughters: \( X^H X^h \)
- Non-carrier Daughters: \( X^H X^H \)
Inheritance Pattern Conclusion
Hemophilia is a sex-linked recessive disorder. The inheritance pattern shows that males are more likely to express the disease because they have only one X chromosome. Females can be carriers if they have one normal and one hemophilia allele but typically do not show symptoms unless they are homozygous recessive (which is rare). The carrier status of females leads to a 50% chance of passing the affected gene to their sons (resulting in hemophilia) and a 50% chance of passing the carrier status to their daughters.
