Need help with Genetics problem!!!?
Need help with Genetics problem!!!? In a species of the cat family, eye color can be gray, blue, green or brown. In separate crosses involving homozygous parents, the following data were obtained. The character (eye color) is inherited by the same mechanism in each cross.
In Cross A, the parents were gray x brown, the F1 offspring were all green, and the F2 were 9:3:3:1 for green, brown, gray, and blue respectively
In Cross B the parents were Green x Brown, F1 were all green, and F2 were 3:1 green and brown respectively
In Cross C the parents were Green x Gray, F1 were all green, and F2 were 3:1 green and gray respectively.
How many genes are involved in the inheritance of eye color?
Devise genetics symbols for these gene(s) and alleles, and indicate the genotypes of the P1 parents for each of the three crosses above.
I'm not totally sure about this, but as no one else is answering...
9:3:3:1 suggests independent assortment of two traits with homozygous parents. Normally that wouldn't be too mysterious (if the traits were hair colour and eye colour, for example 9 with hair colour X and eye colour A, 1 with hair Y and eyes B, and 3 each way), but here they're being combined into one physical phenotype, from our perspective.
So I suggest there are 2 genes, and they sort like this:
default = green
pair of recessives on 1 gene â€“> grey
pair of recessives on other gene â€“> brown
both genes have a pair of recessives â€“> blue
In cross A, the grey cat has a pair of recessives causing grey on gene 1. On gene 2 he has a pair of dominant alleles (dominant for that gene alone) which would normally cause green. Edit. The brown cat has a pair of recessives causing brown on gene 2, with a pair of dominant defaults on her gene 1.
In the first cross you have default for gene 1 (D1), grey for gene 1 (g), default for gene 2 (D2) and brown for gene 2 (b).
ggD2D2 x D1D1bb = all D1gD2b (double default)
In F2 you get a range of green (all those with at least 1 D1 and 1 D2 allele: 9), grey - those with 2g alleles but at least one D2 allele: 3, brown - those with at least 1 D1 allele and 2 b alleles, and 1 solitary blue which is ggbb.
Cross B is simple dominance:
D1D1D2D2 x D1D1bb â€“> all D1D1D2b
F2: 1 D1D1D2D2, 2 D1D1D2b and 1 D1D1bb
Cross C is the same except with
D1D1D2D2 x ggD2D2
(You can't prove green-eyes in B is homozygous for D1, but you're given no reason to think otherwise, so why complicate things? Likewise for green-eyes in C wrt D2.)
Two genes involve in the inheritance of eye color.
A: allele for gray color
B: allele for brown color
Interaction between A and B produces green color; and the absence of A and B will produces blue color.
P: AAbb (gray) x aaBB (brown)
Gamete: AB x ab
F1: AaBb (green)
Gametes: AB, Ab, aB, ab (both parents)
A-B-: 9 green
A-bb: 3 gray
aaB-: 3 blue
aabb: 1 brown
P: AABB (green) x aaBB (brown)
Gamete: AB x aB
F1: AaBB (green)
Gametes: AB and aB (both parents)
F2: AABB, AaBB, AaBB, aaBB (3 green : 1 brown)
P: AABB (green) x AAbb (gray)
Gamete: AB x Ab
F1: AABb (green)
Gametes: AB and Ab (both parents)
F2: AABB, AABb, AABb, AAbb (3 green : 1 gray)
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