In *Drosophila melanogaster*, eye color is an X-linked trait where red eye color (X^R) is … — JAMB UTME

In *Drosophila melanogaster*, eye color is an X-linked trait where red eye color ( $X^R$ ) is dominant over white eye color ( $X^r$ ). If a heterozygous red-eyed female ( $X^R X^r$ ) is crossed with a white-eyed male ( $X^r Y$ ), what is the probability that a female offspring from this cross will express the white-eye phenotype?

A
25%
50%Cevap
C
75%
D
100%

Cevap

50%

The female parent donates either

X^R

X^r

with equal probability (50% each), while the male parent donates an

X^r

chromosome to all female offspring. As a result, 50% of the female offspring inherit

X^R X^r

(red-eyed) and 50% inherit

X^r X^r

(white-eyed).

Adım Adım Çözüm

Determine parental genotypes and gamete contributions.

Female genotype is

X^R X^r

(gametes:

X^R

and

X^r

); Male genotype is

X^r Y

(gametes:

X^r

and

Y

The gene for eye color in Drosophila is located on the X chromosome.

Construct the genetic cross to find offspring genotypes.

Offspring genotypes are

X^R X^r

(red-eyed female),

X^r X^r

(white-eyed female),

X^R Y

(red-eyed male), and

X^r Y

(white-eyed male). Each genotype represents 25% of total offspring.

Combining maternal and paternal gametes yields four equally likely genotypic outcomes.

Restrict the calculation specifically to female offspring.

Female offspring genotypes are

X^R X^r

and

X^r X^r

. One out of two female offspring (

X^r X^r

) has white eyes, giving a probability of

\frac{1}{2} = 50\%

The question specifically asks for the probability among female offspring, not among all offspring.

Anahtar Kavram

X-linked recessive inheritance and gender-restricted offspring probability calculations

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Adım Adım Çözüm

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