Use appropriate genetic cross to explain: XX-XY XX-XO methods of sex determination. (12 mrks)

• Mother (due to non-disjunction): Produces an $XX$ egg.
• Father (normal): Produces $X$ or $Y$ sperm.

If the $XX$ egg from the mother is fertilized by a normal $Y$ sperm from the father:

• Offspring genotype: $XXY$
• Offspring phenotype: Male with Klinefelter's Syndrome (characterized by features such as reduced fertility, taller stature, and some feminized physical traits).

5. (b) A carrier of haemophilia marries a normal male. Show the chances of their offspring getting haemophiliac.
Haemophilia is an X-linked recessive disorder. Let $X^H$ be the normal allele and $X^h$ be the haemophilia allele.

• Carrier female genotype: $X^H X^h$
• Normal male genotype: $X^H Y$

• Female ($X^H X^h$): Gametes are $X^H$ and $X^h$.
• Male ($X^H Y$): Gametes are $X^H$ and $Y$.

• $X^H X^H$: Normal female
• $X^H Y$: Normal male
• $X^H X^h$: Carrier female
• $X^h Y$: Haemophiliac male

Only the $X^h Y$ genotype results in a haemophiliac child.
The chance of having a haemophiliac child is $\frac{1}{4}$.

The chance of their offspring getting haemophiliac is $\boxed{\text{25\%}}$.

5. (c) State two factors that are revealed in a blood group test.

• The specific ABO blood type (e.g., A, B, AB, or O).
• The Rh factor status (positive or negative).