I need some help please on the problem below. As you can see I have already comp
ID: 270208 • Letter: I
Question
I need some help please on the problem below. As you can see I have already completed the 1st half of the problem asking to label the recombinants. But I am unsure of how to do the second part of calculations.
Suppose you discovered the same disorder and blood type genes in an animal where you are able to set up experimental crosses. In addition, you are considering a third possibly linked gene we will call T. You want to know where all three genes, H, I, and T are on a chromosome relative to one another, so you set up a test cross.
You start with the parents HiT/HiT x hIAt/hIAt and the resulting progeny in F1 are crossed in a testcross as such:
HiT/hIAt x hit/hit and get the following:
Progeny Type
Numbers
Recombinant?
H i T
400
Parental
h I t
380
Parental
H i t
60
Single
h I T
53
Single
h i T
57
Single
H I t
55
Single
H I T
3
Double
h i t
2
Double
Total
1000
In the table, state which is parental, and which are single and double crossovers. Then, calculate the recombination frequencies and the distances between H, I and T, and map their locations relative to one another on a chromosome.
Progeny Type
Numbers
Recombinant?
H i T
400
Parental
h I t
380
Parental
H i t
60
Single
h I T
53
Single
h i T
57
Single
H I t
55
Single
H I T
3
Double
h i t
2
Double
Total
1000
Explanation / Answer
Parental genotypes are - HiT & hIt.
Double crossovers are - HIT & hit.
In double crossover, only the gene located in middle changes its position relative to other genes.
Therefore, gene I/i is located in middle and gene order is HiT / hIt.
RF (in %) = [No. of single crossovers + double crossovers DCO / Total progeny]*100
If RF = 1% , it means two genes are located 1 map units (m.u.) or 1 centi Morgan (cM) apart.
*******************
= [55 + 57 + 3 + 2 / 1000]*100 = 11.7 %
Distance between H and i genes = 11.7 m.u.
= [60 + 53 + 3 + 2 /1000]*100 = 11.8 %
Distance between i and T genes = 11.8 m.u.
***************
Genetic map showing their locations :-
I----------------------------------------I----------------------------------------I
H---------- 11.7 m.u.-------------- i ------------- 11. m.u.--------------T