Question

1. (1 point) An organism of genotype AaBbDd was test-crossed to a triply recessive individual (aabbdd). The genotypes of the offspring were as follows:

Genotype          number of offspring                           Genotype        number of offspring

AaBbDd          20 AaBbdd         20     

aabbDd          20    aabbdd         20

AabbDd          5 Aabbdd         5

aaBbDd          5                   aaBbdd         5

1. Only 2 of the three genes are linked together on the same chromosome. Which gene is on a chromosome on its own? Hint: Look at the data only two genes at a time and look for evidence of independent assortment.
2. Calculate the map distance between the two genes that are linked.

Answer 1

A).

Gene A and B are linked. Gene D is unlinked and assorted independently.

Dihybrid (AB/ab; Dd) x tester (ab/ab; dd)----- testcross

AB/ab; Dd genotype produces 8 types of gametes as below:

Recombinant Gametes :

AbD=5

Abd=5

aBD=5

aBd=5

Non-recombinant gametes:

ABD=20

ABd=20

abD= 20

abd=20

ab/ab; dd genotype produces only one type of gametes, and.

If we deduct and from each genotype, we can get gametes of trihybrid.

B).

Recombination frequency (RF)= (no. of recombinants/total progeny)100

RF =(20/100)100= 20%

RF(%)= Distance between genes (mu)

20%=20mu

Distance between the two linked genes = 20 mu