Research Area: Mechanisms in Early Meiosis
Sexual Reproduction
During sexual reproduction, the genetic material from two parent organisms combines to give rise to a genetically distinct, though related, offspring. In order to prevent the relentless accumulation of DNA through generations, the chromosomal content is halved in the parent germline, yielding haploids. Meiosis is the process that generates the haploids from the diploid progenitor. As such, meiosis is key to maintaining chromosomal content, in a species.
Meiosis follows a defined sequence of events, starting with DNA synthesis (S-phase), where chromosomes are replicated to form identical sister chromatids, linked by cohesin rings. During meiosis, however, it is necessary to link homologous chromosomes (homologs). The cell makes programmed double strand breaks (see below) in its own genome, which are then repaired via homologous recombination. In meiosis, the repair of these DNA breaks is directed to the homologs. Some breaks are repaired as crossovers which link the homologs together. Once linked, the homologous chromosomes are separated (end of meiosis I), and the sisters are subsequently separated (meiosis II).
Meiotic Double Strand Breaks
Making breaks is a prerequisite to linking homologs. However, due to the catastrophic damage unchecked DNA breaks can cause in a cell, meiotic double strand breaks are carefully regulated. The meiotic break machinery is associated with the chromosomal axis proteins (yellow) via a trimeric complex (green). Breaks are made by a topoisomerase-like protein (red) but are directed to chromosomal loops via histone marks. Part of the DNA repair machinery (purple) is also required in order for breaks to be made.
How is double strand break formation controlled?
How are crossovers regulated to ensure all homologs are linked?
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