Question

X^B x X^BY
What proportion of the male children are colourblind
What proportion of the female
children are colourblind

Answer 1

To determine the proportion of colorblind male and female children from a genetic cross involving colorblindness, we need to understand how colorblindness is inherited. Colorblindness is typically an X-linked recessive trait, which means the associated gene is located on the X chromosome.

Assuming:
- \(X^B\) represents the normal vision allele.
- \(X^{b}\) represents the colorblind allele.

To analyze the offspring, we can define the genotypes of the parents. Let’s consider a typical scenario:

1. **Male parent (XY)**:
- If the male has normal vision, his genotype is \(X^B Y\).
- If the male is colorblind, his genotype is \(X^{b} Y\).

2. **Female parent (XX)**:
- If the female has normal vision, her possible genotypes could be \(X^B X^B\) (homozygous normal) or \(X^B X^{b}\) (heterozygous carrier).
- If the female is colorblind, her genotype is \(X^{b} X^{b}\).

### Example Scenarios

#### Scenario 1: Normal Vision Male (X^B Y) with Carrier Female (X^B X^b)

**Punnett Square:**

\[
\begin{array}{c|c|c}
& X^B & X^b \\
\hline
X^B & X^B X^B & X^B X^b \\
\hline
Y & X^B Y & X^b Y \\
\end{array}
\]

**Offspring Genotypes:**
1. \(X^B X^B\) (Normal Female) - Female
2. \(X^B X^b\) (Carrier Female) - Female
3. \(X^B Y\) (Normal Male) - Male
4. \(X^b Y\) (Colorblind Male) - Male

**Proportions:**
- Males: 1 colorblind male out of 2 males ⇒ Proportion = \(0.5\) (50%)
- Females: 0 colorblind females out of 2 females ⇒ Proportion = \(0.0\) (0%)

#### Scenario 2: Normal Vision Male (X^B Y) with Colorblind Female (X^{b} X^{b})

**Punnett Square:**

\[
\begin{array}{c|c|c}
& X^{b} & X^{b} \\
\hline
X^B & X^B X^{b} & X^B X^{b} \\
\hline
Y & X^{b} Y & X^{b} Y \\
\end{array}
\]

**Offspring Genotypes:**
1. \(X^B X^{b}\) (Carrier Female) - Female
2. \(X^B X^{b}\) (Carrier Female) - Female
3. \(X^{b} Y\) (Colorblind Male) - Male
4. \(X^{b} Y\) (Colorblind Male) - Male

**Proportions:**
- Males: 2 colorblind males out of 2 males ⇒ Proportion = \(1.0\) (100%)
- Females: 0 colorblind females out of 2 females ⇒ Proportion = \(0.0\) (0%)

### Conclusion
- The proportions of colorblind males and females depend on the genotypes of the parents involved in the cross.
- In general:
- Males can be colorblind if they inherit \(X^{b} Y\).
- Females can only be colorblind if they inherit two copies of the colorblind gene (\(X^{b} X^{b}\)).

If you provide specific parental genotypes, I can provide a more tailored answer.