Meiosis - of heterozygous individuals Organisms(normally...

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Meiosis Sexual reproduction occurs only in eukaryotes . During the formation of gametes , the number ofchromosomes is reduced by half, and returned to the full amount when the two gametes fuse duringfertilization . Ploidy | Haploid and diploid are terms referring to the number of sets of chromosomes in a cell. Gregor Mendel determined his peas had two sets of alleles, one from each parent. Diploid organisms are those with two (di) sets. Human beings (except for their gametes), most animals and many plants are diploid. We abbreviate diploid as 2n. Ploidy is a term referring to the number of sets of chromosomes. Haploid organisms/cells have only one set of chromosomes, abbreviated as n. Organisms with more than two sets of chromosomes are termed polyploid. Chromosomes that carry the same genes are termed homologous chromosomes . The alleles on homologous chromosomes may differ, as in the case
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Unformatted text preview: of heterozygous individuals. Organisms (normally) receive one set of homologous chromosomes from each parent. Meiosis is a special type of nuclear division which segregates one copy of each homologous chromosome into each new "gamete". Mitosis maintains the cell's original ploidy level (for example, one diploid 2n cell producing two diploid 2n cells; one haploid n cell producing two haploid n cells; etc.). Meiosis, on the other hand, reduces the number of sets of chromosomes by half, so that when gametic recombination (fertilization ) occurs the ploidy of the parents will be reestablished. Most cells in the human body are produced by mitosis. These are the somatic (or vegetative) line cells. Cells that become gametes are referred to as germ line cells . The vast majority of cell divisions in the human body are mitotic, with meiosis being restricted to the gonads ....
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