AP Biology 11
Linkage Maps (Genetic Maps)
Genetic mapping experiments are accomplished by a testcross

A test cross occurs when you mate an individual that is ______________________ for two or
more genes and one that is _________________ recessive for the same genes
Genes that are located on ____________chromosomes show a recombination frequency of 50%
Genes that are located _______________on the same chromosome show a recombination frequency
of 50%
The ________________two genes are to each other on the chromosome, the ___________the
recombination frequency will be.
Experimentally, the _______________of recombinant offspring is correlated with the
_________________between the two genes.


If the genes are far apart → more recombinant offspring
If the genes are close → fewer recombinant offspring
Map distance = Number of recombinant offspring
x 100
Total number of offspring
*One map unit is equivalent to 1% recombination frequency.
Practice
1. The following recombination frequencies have been determined for several gene pairs. Create
a linkage map for these genes, showing the map unit distance between loci.
j-k: 12%
j-m: 9%
k-l: 6%
l-m: 15%
2. In guinea pigs, black(B) is dominant to brown (b), and solid color (S) is dominant to spotted (s).
A heterozygous black, solid-colored pig is mated with a brown, spotted pig.
The offspring from several litters are as follows: black solid: 16; black spotted: 5; brown solid: 5;
and brown spotted: 14.
Are these genes linked or unlinked?
If they are linked, how many map units are they apart?