Question

The following figure represents experimental results from study designed after the Beadle and Tatum experiment. Assume the mutants are homozygous for recessive alleles causing their phenotypes.

	Nutrient A	Nutrient B	Nutrient C	Nutrient D
Mutant 1	No	Yes	Yes		No
Mutant 2	Yes	Yes	Yes		No
Mutant 3	Yes	Yes	Yes		Yes
Mutant 4	No	No	Yes		No
Mutant 5	No	Yes	Yes		No

1.) ordered pathway for mutants and nutrients?

Ex: (Precursor ----M1----> Nut1 ----M2----> Nut2 ----M3---> Nut3 ----m4---> Nut4)

2.). If you crossed mutants 1 and 5, what would the nutrient requirements of the offspring be?

3.) . If you crossed mutants 1 and 4, what would the nutrient requirements of the F₁ be?

4.)If you conducted an F₁xF₁ cross of mutants 1 and 4, what would the phenotypic ratios of the F₂ be?

Answer 1

•M1 -- Nut B ---Nut C --- M2---Nut A---Nut B ---Nut C--- M3---Nut A ---Nut B ---Nut C ---Nut D ---M4 --- Nut C ---M5 ---Nut B --- Nut C.

•M1 à Nut B àNut C à M2àNut A à Nut B àNut C à M3àNut A à Nut B àNut C àNut D à M4 à Nut C à M5 à Nut B àNut C

•Cross between M1 and M5 the offspring required the nutrients B and nutrient C. because both the mutants are lacking these two . And from the given data we know that mutants express only in recessive condition . Both are having recessive homozygous condition for B and C [bbcc] so after cross also these two combination also produced homozygous recessive condition.

•Cross between M1 and M4 the F1 offspring required nutrient is “C”. Because M1 is homozygous recessive for bbcc but dominant AA,DD. And M4 is homozygous recessive for cc but dominant AA,DD , BB . After cross on c allele will come in homozygous recessive condition .

•The F1 progeny shows genetic combination of above cross- AABbccDD.

•Here A and D are homozygotic and non mutated , cc homozygotic and mutated , Bb is heterozygotic express normal nutrient but carrier of b .

•After self cross of AABbccDD    X     AABbccDD.

•We just focus on the Bbcc – in the F2 progeny all will produce Nutrient A, Nutrient D.   All are mutated for Nutrient C .

But for Nutrient B the phenotypic ratio is 3:1 [3 normal : 1 mutatnt].

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