Males have one X chromosome and one Y chromosome. Females have two X chromosomes. Males inherit the X chromosome from the mother and the Y chromosome from the father. Females inherit one copy of the X chromosome from each parent. The bar eye is X-linked and alleles are incompletely dominant.
Let X
B be the wildtype allele on the X chromosome for wildtype-shaped eyes
Let X
b be the mutant allele on the X chromosome for bar-shaped eyes
In incomplete dominance, the heterozygotes (X
BX
b) exhibit kidney-shaped eyes which is a blend of two phenotypes.
The purple eye is an autosomal recessive trait. In autosomal recessive inheritance, the presence of two copies of recessive alleles is required to exhibit the trait.
Dominant P allele = red eyes
Recessive p allele = purple eyes
In X-linked inheritance, there is no male-to-male transmission of trait
Genotype of parents:Genotype of bar-shaped, red-eyed female parent: X
bX
b PP
Genotype of normal-shaped, purple-eyed male parent: X
BY pp
Parent cross: XbXb PP * XBY ppGametes | XbP | XbP |
XBp | XBXb Pp | XBXb Pp |
Yp | XbY Pp | XbY Pp |
F1 offspring phenotypic ratio: F1 males: 100% bar eye (60 facets), red eyes (X
bY Pp)
F1 females: 100% kidney-shaped (447 facets), red eyes (X
BX
b Pp)
Thus, all F1 offspring will have red eyes. F1 females will have kidney shaped eyes. F1 males will have bar shaped eyes.
F1 * F1: X
BX
b Pp * X
bY Pp
See attachment!
Therefore, all individuals with kidney-shaped eyes are females. Males do not have kidney shaped eyes because they have only one X chromosome.
All F1 offspring have red eyes. All F1 females have kidney-shaped eyes and all F1 males have bar-shaped eyes.
F2 phenotypic ratio:kidney-shaped, red-eyed female = 3/16
kidney-shaped, purple-eyed female = 1/16
bar-shaped, red-eyed female = 3/16
bar-shaped, purple-eyed female = 1/16
wildtype-shaped, red-eyed male = 3/16
wildtype-shaped, purple-eyed male = 1/16
bar-shaped, red-eyed male = 3/16
bar-shaped, purple-eyed male = 1/16
A) The correct option is d. F1 females will have kidney-shaped (447 facets) red eyes, and males will have Bar eye (60 facets) red eyes
B) The correct option is c. 3/16 red-eyed females with Bar eyes; 1/16 purple-eyed females with Bar eyes; 3/16 red-eyed females with kidney-shaped eyes; 1/16 purple-eyed females with kidney-shaped eyes.
C) The correct option is b. 3/16 red-eyed males with Bar eyes; 1/16 purple-eyed males with Bar eyes; 3/16 wild-eyed males with red eyes; 1/16 purple-eyed males with wild-shaped eyes