Question

X=unaffected X chromosome, x=X chromosome affected by hemophilia, and Y=Y chromosome. If an Xx female and a XY male have children, what fraction of their offspring will have an affected chromosome and what fraction is likely to be affected by hemopilia?

1/4 and 1/4
1/2 and 1/4
1/2 and 1/3
1/4 and 1/2

Answer 1

To analyze the inheritance of hemophilia in the offspring of an Xx female (heterozygous for hemophilia) and an XY male, we can set up a Punnett square.

1. The possible gametes from the Xx female: X (unaffected) and x (affected).
2. The possible gametes from the XY male: X (unaffected) and Y (male).

Now let's create the Punnett square:

```
X Y
----------------
X | XX XY |
----------------
x | Xx xY |
----------------
```

From this Punnett square, we can determine the genotypes of the offspring:

- XX: Female, unaffected
- XY: Male, unaffected
- Xx: Female, carrier (unaffected but has one affected X)
- xY: Male, affected by hemophilia

Now we can count the fractions:

1. **Fraction of offspring with an affected chromosome (which means they have at least one x):**
- The offspring could be XX (no affected chromosome), XY (no affected chromosome), Xx (one affected), or xY (one affected).
- The affected X chromosomes can be contributed by Xx and xY.
- Two of the four scenarios have an affected X chromosome: Xx and xY.
- So, the fraction of offspring with an affected chromosome = 2 out of 4 = 1/2.

2. **Fraction of offspring likely to be affected by hemophilia:**
- Only the children with genotype xY are affected (only one child out of four).
- So, the fraction of affected offspring = 1 out of 4 = 1/4.

Thus, the answer is:

**1/2 (for having an affected chromosome) and 1/4 (for being affected by hemophilia).**

The correct answer is **1/2 and 1/4**.