Ch 7 – Linkage, Recombination, Eukaryotic Gene Mapping 02/25/2014
7.1 – Linked Genes Do Not Assort Independently
linked genes – genes that are located close together on the same chromosome and belong to the same
not expected to assort independently
7.2 – Linked Genes Segregate Together and Crossing Over Produces Recombination Between Them
genes that are close together on the same chromosome are inherited together
crossing over results in recombination
linkage and crossing over are like opposites – linkage keeps things together and crossing over mixes them
Complete Linkage Compared with Independent Assortment
Test cross reveals the effects of linkage
With complete linkage, only nonrecombinant progeny are produced
With independent assortment, half the progeny are recombinant and half the progeny are not
Nonrecombinant gametes – gametes that only contain original combinations of alleles present in
Recombinant gametes – gametes with new combos of alleles
Crossing Over with Linked Genes
For each meiosis in which a single crossover takes place, two nonrecombinant and two recombinant
gametes will be produced.
For closely linked genes, crossing over doesn’t take place in every meiosis.
If there is a single crossover, half the gametes are recombo and half are nonrecombo.
So the total percentage of recombo’s is always half the percentage of meiosis in which crossing over takes
Calculating Recombination Frequency
( # of recombinant progeny / total # of progeny ) x 100
Coupling and Repulsion