In pea plants, flower position can be axial or terminal and stem length can be long or dwarf. Axial flower position is dominant over terminal; and long stem length is dominant over dwarf. Pea plants heterozygous for both traits are allowed to self-pollinate in a dihybrid cross. 400 of the resulting seeds are planted. How many offspring would be predicted to have terminal flowers and be dwarf?

25

Explanation:

Let stem length be represented by T and t alleles ( T is dominant over t ) and flower position be represented by A and a alleles ( A is dominant over a ).

A dihybrid cross of heterozygous pea plants will give progeny in following ratio:

TtAa  X  TtAa :

T_A_ = 9

ttA_   = 3

T_aa  = 3

ttaa     = 1

So, the ratio will be 9:3:3:1 where dwarf, terminal flower plant (ttaa) will be 1/16.

If 400 seeds are planted, (1/16)*400 = 25 plants will be expected to be dwarf with terminal flowers.

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