white o x red 9(heterozygote from F1) 1 red: 1 white with white being a recessive trait. the most informative cross is the reciprocal of the In this case equal numbers of males and females have white eyes. Again this is consister first cross white 9 x red o(wild type) red 9, white O Ignoring the sex of the flies, it looks as if a wild type d is heterozygous: the wild type allele is always passed on to the daughters and the white allele is passed on to sons The explanation is that eye color gene is on the sex determining chromosome X. males only have one copy of the x chromosome and daughters always get one copy of the X from the mother and one copy from the father Xy Xw= white allele on×,X+= red allele onⅩ XWⅩwxx+y Xwy red white Thus, the trait for red eyes is always inherited along with the X chromosome from the father. The absence of red giving white eyes)always goes with the y chromosomewhite O x red O (heterozygote from F1) ↓ 1 red : 1 white In this case equal numbers of males and females have white eyes. Again this is consistent with white being a recessive trait. The most informative cross is the reciprocal of the first cross. white O x red O (wild type) ↓ red O , white O Ignoring the sex of the flies, it looks as if a wild type is heterozygous: the wild type O allele is always passed on to the daughters and the white allele is passed on to sons. The explanation is that eye color gene is on the sex determining chromosome X. Males only have one copy of the X chromosome and daughters always get one copy of the X from the mother and one copy from the father. (XX) x (XY) XX XY O O Xw = white allele on X, X+ = red allele on X XwXw x X+Y ↓ XwX+ XwY red O white O Thus, the trait for red eyes is always inherited along with the X chromosome from the father. The absence of red (giving white eyes) always goes with the Y chromosome