Meiosis is the process that takes place in sexual reproduction; it functions to produce four daughter cells with one half the number of chromosomes as the parent cell – reducing two sets of diploid to haploid. There are two stages of meiosis: Meiosis I and Meiosis II. In Meiosis I, homologous chromosomes bind along length so crossing over occurs at the chiasmata, to produce four sister chromatids. Two sister chromatids are pulled to each pole by spindle fibers, a cleavage furrow develops – the end product of Meiosis I are two haploid cells, each containing duplicated copy of homologous chromosome. The two cells undergo Meiosis II, where spindle fibers form once again to pull apart the sister chromatids to opposite poles. A cleavage furrow forms, producing four haploid daughter cells.
Linkage is the probability of genes located near each other on chromosomes to be inherited during meiosis. The loci is the specific position a gene is located at on a chromosome, and genes in proximity to each other are more likely to be transferred to the same chromatids during crossover. Crossover frequency indicates how far genes are from each other on the chromosome, a higher crossover frequency gives rise to a larger distance between two genes.
A genetic map unit (m.u.) refers to the ‘distance between genes for which one product of meiosis is 100 recombinant’1 – this value indicates the distance between genes. A linkage map can be produced by mapping the traits on the same chromosome; this can give information on the loci of genes that cause genetic diseases.
1. Griffiths, A.J.F., Miller, J.H., & Suzuki D.T. (2000). Linkage Maps. (7th ed.) An Introduction to Genetic Analysis. New York, NY: W.H. Freeman