Four possibly different albino strains of Neurospora were each crossed to wild t

Question

Four possibly different albino strains of Neurospora were each crossed to wild type. All crosses resulted in 1/2 wild-type and 1/2 albino progeny. Crosses were made between the first strain and the other three with the following results: 1x2: 975 albino : 25 wild type, 1x3: 1000 albino, 1x4: 750 albino : 250 wild type.

What is happening on each of these crosses; in other words, which mutations represent different genes and which of those genes seem to be linked? How did you arrive to these conclusions? Please, explain your answer.

Explanation / Answer

Genes 1 and 2 are linked because they generate less than 25% wild-type. 25% wild-type is required for independent assortment, the different recombinant(the double mutant) being among the albino progeny.

The 25 wild types in the 1 × 2 cross are probably followed by the albino, double mutant with almost identical frequency.

The real RF is thus about 50/1000, or 5%.

The expectation of independent assortment is achieved in the 1 × 4 cross.

The 1 × 3 cross shows that the two mutations are allelic because they fail to produce any recombinants amongst a sizable progeny.

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