Question

If the a and b loci are 30 CM apart and an AA BB individual and an aa bb individual mate: What gametes will the F1 individuals produce, and in what proportions? What phenotypic classes in what proportions are expected in the F2 generation (assuming complete dominance for both genes) (show procedure, NO score for direct result)?

Answer 1

Answer :)

The a and b alleles are 30 cM are apart. Therefore, there is a 30% recombination between both alleles.

Mating between AABB and aabb:

AABB             x          aabb

Gametes          AB                               ab

F1 progeny                  AaBb

F1 offspring are recombinant and only one genotype. Therefore, 100% proportion of offspring by F1 offspring.

F1 mating:

AaBb               x                      AaBb

Gametes	AB	Ab	aB	ab
AB	AABB	AABb	AaBB	AaBb
Ab	AABb	AAbb	AaBb	Aabb
aB	AaBB	AaBb	aaBB	aaBb
ab	AaBb	Aabb	aaBb	aabb

Genotypes AABB, AABb, AaBB, AaBb, AABb, AaBb, AaBB, AaBb, and AaBb will have the same phenotype.

Genotypes AAbb Aabb Aabb will have one phenotype.

Genotypes aaBB aaBb aaBb will have one phenotype.

Genotype aabb has a different phenotype.

The genotypes AAbb Aabb Aabb aaBB aaBb aaBb are recombinants.

These will share 30% of offspring.

Total offspring are 16,

30% offspring = 16 x 30%

30% offspring = 4.8

Therefore, recombinants shares 4.8 proportions.

Recombinants genotypes AAbb Aabb Aabb proportion = 4.8/2

Recombinants genotypes AAbb Aabb Aabb proportion = 2.4

Recombinants genotypes aaBB aaBb aaBb proportion = 4.8/2

Recombinants genotypes aaBB aaBb aaBb proportion = 2.4

Rest proportion = 16 – 4.8

Rest proportion = 11.2

Divide them into dominant and recessive phenotypes.

Because dominant genotypes and recessive have 9:1 ratio, therefore:

9x + 1x = 11.2

x = 0.112

The proportion of dominant phenotypes = 9 x 0.112

The proportion of dominant phenotypes = 1.008

The proportion of recessive phenotypes = 0.112

Therefore, the ratio of F2 phenotypes:

1.008 : 2.4 : 2.4 : 0.112

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