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In order to find out the different types of gametes produced by a pea plant having the genotype AaBb, it should be crossed to a plant with the genotype -
A
AaBb
B
aabb
C
AABB
D
aaBB
Detailed Solution
To find out the types of gametes produced by a plant, it is crossed with a plant that is homozygous recessive for both genes. This is a test cross.
The double recessive plant aabb produces only one kind of gamete, ab, which contributes only recessive alleles.
So the phenotype of each offspring shows directly the type of gamete contributed by the AaBb plant.
AaBb x aabb gives AaBb, Aabb, aaBb and aabb in the ratio 1 : 1 : 1 : 1, showing that AaBb produces four types of gametes (AB, Ab, aB, ab) in equal proportions.
Crossing with AaBb, AABB or aaBB would hide some of the alleles behind dominant ones.
So it should be crossed with aabb.
The double recessive plant aabb produces only one kind of gamete, ab, which contributes only recessive alleles.
So the phenotype of each offspring shows directly the type of gamete contributed by the AaBb plant.
AaBb x aabb gives AaBb, Aabb, aaBb and aabb in the ratio 1 : 1 : 1 : 1, showing that AaBb produces four types of gametes (AB, Ab, aB, ab) in equal proportions.
Crossing with AaBb, AABB or aaBB would hide some of the alleles behind dominant ones.
So it should be crossed with aabb.