Meiosis involves two subsequent divisions of genetic material. Gametes are referred to as haploid (n), as they contain half the number of chromosomes as the parent cell that they were created from. The testes (male gonads) and the ovaries (female gonads) are the sites of gamete formation, the processes are known as gametogenesis, spermatogenesis and oogenesis.
Meiosis explanation:
Gamete formation occurs in sexually reproducing organisms. During this type of cell production the diploid (2n) number of chromosomes is halved; then is then referred to as a haploid (n), effectively half the number of chromosomes present in the organic cell, the diploid number. Meiosis is a process which not only halves the number of chromosomes in the parent cell; it also introduces genetic variation into the gametes and therefore the resulting zygotes that may eventually be produced.
There are two events that occur during meiosis that help to produce genetic various, these are:
∙ Independent assortment
∙ Crossing over
Independent Assortment:
In human cells there are 23 homologous pairs of chromosomes. This means that during meiosis I there are many different possible arrangements of these pairs.
How homologous chromosomes line up during meiosis I determines, in the end, the combination of chromosomes that end up ends up in each gamete. This is one of the reasons why sexual reproduction produces such astounding genetic variation.
Crossing-Over:
When homologous chromosomes are lined up next to each other during meiosis they also can exchange genes. This occurs at the chiasmata and results in genetic variation of the gamete.
Genetic variation within different species can affect their survival and performance, as the environment is constantly changing genetic variation is paramount. When both copies of a gene are identical the expression of that gene may include traits that are less beneficial to survival or reproduction in particular circumstances. This may lead to physiological or behavioural problems of genetic origin, such as malformed physical structure, poor biochemical balance, improper organ formation and function, altered social behaviour, and susceptibility to disease.
The Torreya taxifolia is considered to be one of the rarest species of Jew in North American. However, in the early Holocene, when the climate in south-eastern North America was cooler and considerably more humid than today, the species was likely more prevalent. As the T. Taxifolia failed to migrate North as the climate changed; it is now today restricted to a few locations in the of the .
