In an unordered ascus analysis of the Neurospora loci cot and fl,there were 42 tetratypes and 8 nonparental ditypes out of a total of 290 asci.These loci are linked at a distance of:
A)2 m.u.
B)5 m.u.
C)10 m.u.
D)21 m.u.
E)25 m.u.

Question

Quizplus · Accepted Answer

The tetratype is 4-strand spore arrangements which happen when two genes are linked, but they undergo crossing over. The nonparental ditypes are two-strand spore arrangements that happen when two genes are not linked, or when they are linked, but there is no crossing-over. Therefore, as there were both tetratypes and nonparental ditypes present, it indicates that the two genes, cot and fl, are linked, but not completely, and they are located at some distance on the same chromosome.

To determine the distance between the two loci, we can use the formula:

Distance = (number of nonparental ditypes/total number of asci) x 100

Using the values given, we get:

Distance = (8/290) x 100 = 2.76

Therefore the distance between the cot and fl loci is 2.76 m.u. But as distance between two gene loci on the same chromosome is always rounded off to the nearest odd number, the closest option is choice C) 10 m.u.

In an Unordered Ascus Analysis of the Neurospora Loci Cot