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

14
and 14
1 fourth and 1 fourth

12
and 13
1 half and 1 third

12
and 14
1 half and 1 fourth

14
and 12

Answer 1

To determine the fraction of the offspring that will have an affected chromosome and the fraction likely to be affected by hemophilia, we need to consider the genetic makeup of the parents:

• The Xx female's genotype is Xx, meaning she has one normal X chromosome and one X chromosome affected by hemophilia.
• The XY male's genotype is XY, meaning he has one normal X chromosome and one Y chromosome.

When they have children, the possible combinations of alleles that they can pass on can be represented in a Punnett square.

The possible gametes from the Xx female are:

1. X (normal)
2. x (affected)

The possible gametes from the XY male are:

1. X (normal)
2. Y

Using this information, we can create a Punnett square:

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

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

1. XX (female - unaffected)
2. XY (male - unaffected)
3. Xx (female - carrier)
4. xY (male - affected)

Now, we can tally the offspring:

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

So, the fraction of offspring (children) that have an affected chromosome (x or xY) is:

• 1 (xY male) out of 4 total offspring = 1/4

The fraction of offspring that is likely to be affected by hemophilia (specifically, boys who have the xY genotype) is:

• 1 (xY male) out of 4 total offspring = 1/4

Thus, the correct answer is: 1/4 and 1/4.