In the Japanese morning glory, purple flower color may be caused by dominant all
ID: 53657 • Letter: I
Question
In the Japanese morning glory, purple flower color may be caused by dominant alleles at either one of two separate gene pairs, A_bb or aaB_. When dominant alleles are present at both gene pairs (A_B_), the flower color is blue, and when both are homozygous recessive (aabb), the color is scarlet. A blue F1 was therefore produced by crossing two different purple types AAbb x aaBB.
A. What phenotypes in what proportion would you expect from crossing this F1 to the AAbb parent?
B. What phenotypes in what proportion would you expect from crossing this F1 to the aaBB parent?
C. For an F1 x F1 cross, what proportion of the offspring would be expected to have purple flower color?
D. For an F1 x F1 cross, what proportion of the offspring would be expected to have blue flower color?
E. For an F1 x F1 cross, what proportion of the offspring would be expected to have scarlett flower color?
Explanation / Answer
A. The phenotypes and their proportion on crossing F1 to AAbb will be:
The cross is
AaBb (F1) x AAbb
Gametes from each parent will now be:
AB, aB, Ab, ab from F1 and Ab from AAbb
Crossing the gametes we will get the following genotypes and phenotypes
AABb (Blue) : AaBb (Blue) : AAbb (Purple) : Aabb (Purple)
= 1:1:1:1
This means that the proportion of phenotype of purple to blue flowers will be 1:1
Blue : Purple = 1:1
B. The phenotypes and their proportion on crossing F1 to aaBB will be:
The cross is
AaBb (F1) x aaBB
Gametes from each parent will now be:
AB, aB, Ab, ab from F1 and aB from aaBB
Crossing the gametes we will get the following genotypes and phenotypes
AaBB (blue) : aaBB (purple) : AaBb (blue) : aaBb (purple)
= 1:1:1:1
This means that the proportion of phenotype of purple to blue flowers will be 1:1
Blue : Purple = 1:1
C. The offspring expected to have purple flower colour can be calculated as:
The cross is between F1 and F1. It will be:
AaBb X AaBb
Gametes from each parent will now be:
AB, aB, Ab, ab and AB, aB, Ab, ab
Crossing the gametes we will get the progeny of each phenotype in the following proportion:
A_B_ (blue) = 9
A_bb (purple) = 3
aaB_ (purple) = 3
aabb (scarlet) = 1
Thus the phenotype ratio for blue: purple: scarlet flower will be 9:6:1. Proportion of offspring expected to have purple color flower will be 6/16
D. The offspring expected to have blue flower colour can be calculated as:
The cross is between F1 and F1. It will be:
AaBb X AaBb
Gametes from each parent will now be:
AB, aB, Ab, ab and AB, aB, Ab, ab
Crossing the gametes we will get the progeny of each phenotype in the following proportion:
A_B_ (blue) = 9
A_bb (purple) = 3
aaB_ (purple) = 3
aabb (scarlet) = 1
Thus the phenotype ratio for blue: purple: scarlet flower will be 9:6:1. Proportion of offspring expected to have blue color flower will be 9/16
E. The offspring expected to have scarlet flower colour can be calculated as:
The cross is between F1 and F1. It will be:
AaBb X AaBb
Gametes from each parent will now be:
AB, aB, Ab, ab and AB, aB, Ab, ab
Crossing the gametes we will get the progeny of each phenotype in the following proportion:
A_B_ (blue) = 9
A_bb (purple) = 3
aaB_ (purple) = 3
aabb (scarlet) = 1
Thus the phenotype ratio for blue: purple: scarlet flower will be 9:6:1. Proportion of offspring expected to have scarlet color flower will be 1/16
AB aB Ab ab AB AABB aABB AABb AaBb aB AaBB aaBB AaBb aaBb Ab AABb AaBb AAbb Aabb ab AaBb aaBb Aabb aabb