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In a diploid cell there are two sets of homologous chromosomes of different parental origin (e.g. a paternal and a maternal set). During the phase of meiosis labeled “interphase s” in the meiosis diagram there is a round of DNA replication, so that each of the chromosomes initially present is now composed of two copies called chromatids ...
Mechanically, the process is similar to mitosis, though its genetic results are fundamentally different. The result is the production of four haploid cells (n chromosomes; 23 in humans) from the two haploid cells (with n chromosomes, each consisting of two sister chromatids) [clarification needed] produced in meiosis I. The four main steps of ...
Chromosome 3 is one of the 23 pairs of chromosomes in humans. People normally have two copies of this chromosome. People normally have two copies of this chromosome. Chromosome 3 spans more than 198 million base pairs (the building material of DNA ) and represents about 6.5 percent of the total DNA in cells .
[3] This is not to be confused with mitosis. Mitosis also has prophase, but does not ordinarily do pairing of two homologous chromosomes. [4] In contrast to the mitosis cycle, during meiosis, the number of chromosomes is reduced by half to create haploid gametes; this reduction is called Haploidization; after fertilization, diploidy is restored.
The two chromosomes which pair are referred to as non-sister chromosomes, since they did not arise simply from the replication of a parental chromosome. Recombination between non-sister chromosomes at meiosis is known to be a recombinational repair process that can repair double-strand breaks and other types of double-strand damage. [2]
[3] [4] When each tetrad , which is composed of two pairs of sister chromatids , begins to split, the only points of contact are at the chiasmata. The chiasmata become visible during the diplotene stage of prophase I of meiosis , but the actual "crossing-overs" of genetic material are thought to occur during the previous pachytene stage.
During the leptotene stage, the duplicated chromosomes - each consisting of two sister chromatids - condense from diffuse chromatin into long, thin strands that are more visible within the nucleoplasm (nucleus contents). The chromosomes become visible as thin threadlike structures known as leptonema under a light microscope. [1]: 27 [2]: 353
This is followed by two cell divisions to generate haploid gametes. After the DNA is replicated in meiosis, the homologous chromosomes pair up so that their DNA sequences are aligned with each other. During this period before cell divisions, genetic information is exchanged between homologous chromosomes in genetic recombination. Homologous ...