<%@LANGUAGE="JAVASCRIPT" CODEPAGE="1252"%> linkage prediction

Genetic 342 A&B

Kenneth G Wilson

Professory of Botany

Linkage Predictions

Linkage destroys the beauty of prediction inherent in genetics. A. H Sturtevant and T. H. Morgan developed mapping to allow prediction. The following calculations allow us to predict assortment outcomes from crosses.

Using map data to predict the progeny of the cross a+b+/ab with ab/ab

Let f =the expected frequency of cross overs

Description genotype P f=.1 N=1000

Parental type one

a+ b+ (1-f)/2 .45 450
Parental type two a b (1-f)/2 .45 450

Recombinant

a+ b f/2 .05 50
Recombinant a b+ f/2 .05 50

Example: If genes a and b are twenty map units apart (ie. f= .2) what is the expected progeny from a cross between an organism that is heterozygous for a and b is test crossed to an organism that is ab/ab. Assume that one parent was a+ b/a+ b. What is the probability that the double recessive will be found in the progeny?

Description genotype P f=.2 N=1000

Parental type one

a+ b (1-f)/2 .40 400
Parental type two a b+ (1-f)/2 .40 400

Recombinant

a b f/2 .10 100
Recombinant a+ b+ f/2 .10 100

The answer is P = 0.10

How does this problem change for three linked loci?

 

oliver

This is our friend Oliver the parrotlet,

Oliver is a true parrot,

the smallest in the world.