This S-phase can be referred to as "premeiotic S-phase" or "meiotic S-phase". Before meiosis begins, during S phase of the cell cycle, the DNA of each chromosome is replicated so that it consists of two identical sister chromatids, which remain held together through sister chromatid cohesion.
The two meiotic divisions are known as meiosis I and meiosis II. In meiosis, DNA replication is followed by two rounds of cell division to produce four daughter cells, each with half the number of chromosomes as the original parent cell. Later on, during fertilisation, the haploid cells produced by meiosis from a male and a female will fuse to create a cell with two copies of each chromosome again, the zygote.Įrrors in meiosis resulting in aneuploidy (an abnormal number of chromosomes) are the leading known cause of miscarriage and the most frequent genetic cause of developmental disabilities. Additionally, prior to the division, genetic material from the paternal and maternal copies of each chromosome is crossed over, creating new combinations of code on each chromosome. It involves two rounds of division that ultimately result in four cells with only one copy of each chromosome ( haploid).
Meiosis ( / m aɪ ˈ oʊ s ɪ s/ ( listen) from Ancient Greek μείωσις ( meíōsis) 'lessening', since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells.
A video of meiosis I in a crane fly spermatocyte, played back at 120× the recorded speed Two gametes fuse during fertilization, forming a diploid cell ( zygote) with a complete set of paired chromosomes. The daughter cells divide again in meiosis II, splitting up sister chromatids to form haploid gametes. In meiosis, the chromosomes duplicate (during interphase) and homologous chromosomes exchange genetic information ( chromosomal crossover) during the first division, called meiosis I. JSTOR ( February 2023) ( Learn how and when to remove this template message).Unsourced material may be challenged and removed.
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