MBG*2040: Linkage, Recombination, and Eukaryotic Gene Mapping

gene linkage

Genes that are present on the same chromosome. Tend to travel together through meiosis.

In test crosses, will result in four classes: two major and two minor.

recombination

The divergence from linkage. The frequency is proportional to the distance between genes. These events are RARE.

The further the respective genes are from each other on the chromosome, the higher the frequency of this happening.

homologous recombination

Occurs during prophase I of meiosis. A tetrad or bivalent is formed. A chiasma is the site where recombination occurs.

tetrad

Four homologous chromatids.

bivalent

A pair of homologous chromosomes.

chiasma

The physical junction between the homologous chromatids. The site where recombination occurs.

crossing over

The act of swapping alleles. ALWAYS HAPPENING but alleles MUST BE DIFFERENT to result in recombination. Happens in a 3D space where chromatids face each other, swapping of alleles can happen to ANY of these chromatids.

map units

The percent recombination is used as a measure of distance between genes. Also known as centiMorgans. Once you reach 50%, it plateaus.

cis

Same side.

trans

Opposite sides.