20-21) (8 Pts) Assume that three pairs of alleles are found in Drosophila: +/x,

ID: 42517 • Letter: 2

Question

20-21) (8 Pts) Assume that three pairs of alleles are found in Drosophila: +/x, +/y, and +/z. As shown by the symbols, each non-wild allele is recessive to its wild-type allele. A cross between female heterozygous at these three loci and homozygous recessive males (xxyyzz) yields the following progeny phenotypes:

Calculate the map distances (in map units) between the genes and draw a map?

a) x to z (6 m.u.) and z to y (7 m.u.)

b) x to z (7 m.u.) and z to y (6 m.u.)

c) x to z (13 m.u.) and z to y (12 m.u.)

d) x to z (12 m.u.) and z to y (13 m.u.) 21)

AND

Calculate coefficient of coincidence?

a) 0.238

b) 0.762

c) 0.381

d) 0.129

01 723418 23443310

Explanation / Answer

Answer is

b) x to z (7 m.u.) and z to y (6 m.u.)

First, we will sort out the given information into 3 categories. Parental, single crossover and double cross overs.

Parental

x + z 430

+ y + 441

Single Cross Overs (SCO)

+ + + 27

x y z 32

x y + 31

+ + z 38

Double Cross Overs (DCO)

x+ + 1

+ y z 0

The distance between x and z is (31+38+1)/1000=0.07 or 7 m. u.

The distance between z and y is (27+32+1)/1000=0.06 or 6 m. u.

Answer is

1)0.238

Coefficient of coincidence=Observed number of double crossovers/ |Expected number of double cross overs=1/1000*0.06*0.07=0.238