Question

Cross 1	Cross 2
Parents Bar-eyed female $\times$ Wild type male	Parents Wild-type Female $\times$ Bar eyed Male
$F_1$ 53 Bar-eyed males 47 Bar-eyed females	$F_1$ 48 Wild-type males 52 Bar-eyed females
Cross 4 $F_1$ flies from cross 1 were mated	Cross 4 $F_1$ flied from cross 2 were mated
$F_2$ 22 Bar-eyed males 51 Bar-eyed females 27 wild-type males 0 Wild-type females	$F_2$ 25 Bar-eyed males 26 Bar-eyed females 27 Wild-type males 25 Wild-type females

Read the passage and answer the following question:
An experiment is carried out to explore the inheritance of the bar-eyed trait in fruit flies. Homozygous bar-eyed and wild-type flies are mated, producing two $F_1$ generations. Then crossing of $F_1$ offsprings produces two $F_2$ generations. Here are the data from those 4 crosses which records one hundred offspring from each cross.
Which of the following would be the genotype for a bar-eyed female in the $F_1$ generation in cross 1?

• A. $BB$
• B. $Bb$
• C. $Wb$
• D. $X^B{X}^b$
• E. $X^b{X}^b$

Answer 1

Answer: (D)

$X^B{X}^b$

The bar eye is a sex-linked dominant trait. Female parent in cross 1 is pure breeding Bar eye ($X^B{X}^B$) while the male parent is pure breeding wild type (XY). The Bar eyed $F_1$ female receives $X^B$ from mother and X from the father; the genotype of heterozygous bar eyed $F_1$ female is ($X^B{X}^b$). It is a sex-linked trait. It is a sex-linked dominant trait; not the recessive one. Thus, the correct answer is option D.