A pair of wild type fruit flies of unknown origin are mated and produce wild type F1 offspring. The F1s are allowed to interbreed and produce an all wild type F2. When the F2s are allowed to interbreed they produce an F3 that is 75% wild type and 25% mutant. If the mutant phenotype is due to a recessive mutation in an autosomal maternal effect gene, what are the genotype of the original parents?

the male genotype = +/+

the female genotype = x/x

Explanation:

From the question; we are being told that:

A pair of wild type fruit flies of unknown origin are mated and produce wild type F1 offspring.

At the tail end of the question, it was stated that:

If the mutant phenotype is due to a recessive mutation in an autosomal maternal effect gene,  what are the genotype of the original parents?

From the two statements above;

We assume to Let the wild type allele be :    +

The gene needed for the cross will be :    +/+ but we don't know yet if it is from the paternal or maternal side.

However, from the second statement; it is said that if the mutant genotype is due to recessive mutation in an autosomal maternal effect gene", we can see a clue here that the mutant genotype = x/x  is coming from the maternal side(female)

SO, we can rewrite this as;

We let the male genotype to be: +/+ since the female genotype is x/x

If a cross occurs between:

+/+    and    x/x  

we have:

               +              +

x             +/x            +/x

x             +/x            +/x

We can see that the statement is true that all the F1 offspring produced wild type offspring.

Now if these traits +/x and +/x undergo a cross for the second filial generation F2; they will definitely produce:   wild types for all the offspring

Finally, from the foregoing, the result of F2 cross will also eventually yield

F3 with 75% wild type and 25% mutant

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