Lecture 9 Genetics Terms

Map units

A unit of measurement for distance along a chromosome, where 1 map unit equals a 1% recombination frequency.

CentiMorgan

Another term for a map unit (cM), representing a 1% chance of recombination between two loci.

Three-point test-cross analysis

A cross designed to map three linked genes simultaneously and determine their order on a chromosome.

Double recombinants

Offspring resulting from two separate crossover events occurring between three linked genes.

Double-crossover

Two simultaneous exchange events of non-sister chromatid segments occurring in a single meiotic division.

Interference (I)

A measure of the degree to which one crossover event in a chromosome region prevents or reduces additional crossovers nearby.

Coefficient of coincidence (c)

The ratio of the observed number of double crossovers to the expected number of double crossovers.

Negative interference

A phenomenon where the occurrence of one crossover increases the likelihood of additional crossovers occurring nearby.

Mapping function

A mathematical formula used to convert observed recombination frequencies into true genetic map distances, correcting for undetected multiple crossovers.