MATERNAL EFFECT SNAIL BREEDING Dextral is Dd, and DD Sinistral is dd But offspri

Question

MATERNAL EFFECT SNAIL BREEDING

Dextral is Dd, and DD

Sinistral is dd

But offsprings phenotypes are dictated by the genotype of the mother's somatic cells.

Part 1) A sinistral female is mated with a sinistral male and only dextral progeny are produced. What is the genotype of the female from this cross?

a) Dd

b) Dd or DD

c) DD

d) dd

I'm pretty sure this one is A, just would like confirmation.

Part 2) A sinistral male (dd) and dextral female (DD) are mated and produce all dextral progeny in the F1 generation. If the F1 progeny are allowed to mate with one another, what percentage of the F2 snails will have a dextral coiling pattern?

So this one is 100% dextral, I am positive of that.

Part 3) If the F2 generation is allowed to interbreed to produce an F3 generation, what percentage of sinistral heterozygotes in the F3 had a mother with the dd genotype?

But like, I have no idea about this one. The options are the following:

A) 33%

B) 25%

C) 66%

D) 100%

Please help an idiot out :)

Explanation / Answer

Part 2] A homozygous sinistral male [dd] is mated with a homozygous dextral female [ DD ]

All the offsprings in the F1 generation will have the genotype Dd i.e. they will be heterozygous dextral.

The heterozygous F1 generation mate among themselves--

Punnett's square--

Genotypes are-- DD, Dd and dd

That makes 25% homozygous dextral

50% heterozygous dextral

25% homozygous sinistral

Phenotypes are-- 75% Dextral and 25% sinistral

So, 75% of the F2 progeny will have dextral coiling.

Part 3] The F2 generation interbreeds to produce F3 generation.

From the above calculation, it is clear that only 25% of the F3 progeny had a mother with a dd genotype.

Hence, the correct option is [B] 25%

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