Consider the following chromosomes and if they are affected by hemophilia.

Question

X = unaffected X chromosome, x = X chromosome affected by hemophilia, and Y = Y chromosome.

If an Xx female and XY male have children, what fraction of their offspring will have an affected chromosome, and what fraction is likely to be affected by hemophilia?

(1 point)
Responses

12
1
2
and 13
1
3
1 half and 1 third

12
1
2
and 14
1
4
1 half and 1 fourth

14
1
4
and 12
1
2
1 fourth and 1 half

14
1
4
and 14
1
4
1 fourth and 1 fourth

Answer 1

To determine the fractions you are asking about, let's analyze the possible offspring of an Xx female and an XY male:

1. Parental Genetic Makeup:

   • Female: Xx (one unaffected X and one affected X)
   • Male: XY (one X and one Y)

2. Offspring Genotypes: When an Xx female and an XY male have children, you can set up a Punnett square to visualize the combinations:

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

   The possible genotypes for the children are:

   • XX (unaffected female)
   • XY (unaffected male)
   • Xx (carrier female, unaffected)
   • xY (affected male)

3. Count of Offspring Combinations: From the Punnett square, we can see:

   • 1 XX
   • 1 Xy
   • 1 Xx
   • 1 xY

4. Outcomes:

   • Fraction of children with an affected chromosome: In this case, the affected chromosome is "x". Looking at the combinations:
     • XX = unaffected (0 affected chromosomes)
     • XY = unaffected (0 affected chromosomes)
     • Xx = has 1 affected chromosome
     • xY = has 1 affected chromosome

   So, 2 out of 4 possibilities (Xx and xY) have an affected chromosome.
   Therefore, the fraction of offspring with an affected chromosome is \( \frac{2}{4} = \frac{1}{2} \).

   • Fraction of children likely to be affected by hemophilia: Affected individuals will show hemophilia if they have the genotype "xY". Only one possibility out of the four results in hemophilia:
     • xY = affected male

   Therefore, the fraction of offspring likely to be affected by hemophilia is \( \frac{1}{4} \).

5. Conclusion: The final answer is:

   • Fraction of offspring with an affected chromosome: \( \frac{1}{2} \)
   • Fraction of offspring likely to be affected by hemophilia: \( \frac{1}{4} \)

So, the correct response is:

• 1 half and 1 fourth.