20. Color blindness is inherited in an X-linked recessive manner. A woman who ca

Question

20. Color blindness is inherited in an X-linked recessive manner. A woman who carries the colorblind gene and has normal vision and a man who is colorblind just got married and are wondering about their children.

What is the probability of a colorblind child? Draw a Punnett square

a. What proportion of the sons are colorblind?

b. What proportion of the daughters are colorblind?

c. Now draw a Punnett square of a mating between a colorblind woman and a man with normal vision.

d. What is the probability of a colorblind child?

e. What proportion of the sons are colorblind?

f. What proportion of the daughters are colorblind?

g. Why do sex-linked recessive traits appear more often in males than in females?

Explanation / Answer

20. Color blindness is inherited in an X-linked recessive manner. A woman who carries the colorblind gene and has normal vision and a man who is colorblind just got married and are wondering about their children.

Woman                         Man                                        (Baby) the possible genotypes of offspring

(Normal vision)              (Colorblind)

XCX                          X         XCY                               =           XCXC     / XCY     / XCX   / XY

X   

Y

XC

XCXC  

XCY

X

XCX

XY

What is the probability of a colorblind child? Draw a Punnett square

Ans) 1/2

a. What proportion of the sons are colorblind?

Ans) one or 25%

b. What proportion of the daughters are colorblind?

Ans) one or 25%

c. Now draw a Punnett square of a mating between a colorblind woman and a man with a normal vision.

Woman                         Man                                        (Baby) the possible genotypes of offspring

(Colorblind)                   (Normal vision)

XCXC                          X         XY                               =           XCX     / XCY     / XCX / XCY

X   

Y

XC

XCX

XCY

XC

XCX

XCY

d. What is the probability of a colorblind child?

Ans) 1/2

e. What proportion of the sons are colorblind?

Ans) 1/2 or 50%

f. What proportion of the daughters are colorblind?

Ans) zero

g. Why do sex-linked recessive traits appear more often in males than in females?

Because they carry only one X chromosome and they have only one allele but females have two XX chromosomes if one allele on one X chromosome is inactivated the other X chromosome has normal allele which will prevent the disease development.due having single X chromosome sex-linked recessive traits appear more often in males than in females.

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X   

Y

XC

XCXC  

XCY

X

XCX

XY

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