Overview of Meiosis
During meiosis, homologous chromosomes separate and go to different daughter cells. This diagram shows just the nuclei of the cells. Meiosis, from the Greek word meioun, meaning " make small," refers to the specialized process by which germ cells divide to produce gametes.
Because the chromosome number of a species remains the same from one generation to the next, the chromosome number of germ cells must be reduced by half during meiosis. To accomplish this feat, meiosis, unlike mitosis, involves a single round of DNA replication followed by two rounds of cell division . Meiosis also differs from mitosis in that it involves a process known as recombination, during which chromosomes exchange segments with one another. As a result, the gametes produced during meiosis are genetically unique with each one of them containing 23 chromosomes .
Crossing over is an important phase in meiosis which results recombinants
Meiosis is a special type of cell division necessary for sexual reproduction in eukaryotes. The cells produced by meiosis are gametes or spores. In many organisms, including all animals and land plants, gametes are called sperm and egg cells.
Whilst the process of meiosis bears a number of similarities with the 'life – cycle& cell division process of mitosis, it differs in two important respects:
- The chromosomes in meiosis undergo a recombination which shuffles the genes producing a different genetic combination in each gamete, compared with the co – existence of each of the two separate pairs of each chromosome (one received from each parent) in each cell which results from mitosis.
- The outcome of meiosis is four (genetically unique) haploid cells, compared with the two (genetically identical) diploid cells produced from mitosis.
Meiosis begins with one diploid cell containing two copies of each chromosome – one from the organism's mother and one from its father – and produces four haploid cells containing one copy of each chromosome. Each of the resulting chromosomes in the gamete cells is a unique mixture of maternal and paternal DNA, resulting in offspring that are genetically distinct from either parent. This gives rise to genetic diversity in sexually reproducing populations. This genetic diversity can provide the variation of physical and behavioral attributes (phenotypes) upon which natural selection can act, but, origin and function of meiosis, the genetic diversity may be largely a by – product of the homologous recombination.