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Meiosis promotes varying traits in organisms by recombining genes in the sex cells. Recombination takes place when an individual that inherited AB x ab produces in its gametes Ab and aB, in addition to the inherited AB and ab. And vice-versa, of course.
This takes place by two mechanisms:
- If A/a and B/b are linked (in the same chromosome pair), by crossover in at prophase I;
- If A/a and B/b are unlinked (each in a different chromosome pair), by random orientation of the bivalents at metaphase I.
Another aspect to consider is that once chromosomes pair off, some genes are more dominant than others. For this reason, a particular trait might not show up on the phenotype (physical appearance or trait showing up on a child born) but be carried latently, only to show up again in a following generation (when not "outdone" by a dominant gene). This latent or invisible genetic code is called the genotype.
Sometimes (eye colour being an example) there is not an arbitrary "all or none" principle at work but a sharing of the two traits going on. For this reason, a blue-eyed (recessive gene) man and a brown-eyed (dominant gene) woman may have a hazel or green-eyed child.
Other traits are known to be sex-related or sex-linked. For example, baldness is usually a masculine trait but is inherited by the phenotype's mother. Other traits more prevalent in (but not always so) the male sex are colour-blindness, haemophilia, and even dyslexia. This is because the X chromosome (carried by the female)is physically more "complete" than the Y(carried by the male).
Meiosis is the process of how our sex cells divide. This process randomly splits up your cells so that you only get one copy of each gene/trait from both of the parents. Through meiosis, chromosomes are randomly chosen from the parent's genes and put into the egg or sperm in a random combination such that a fertilized egg would then have 46 chromosomes. This promotes varying traits in organisms by creating a random selection process by which the results can be different each time, even with the same parent donors. Also, the unfertilized egg or the sperm will contain two sets of gene/trait choices and the fertilized egg has four donors. In addition, it promotes diversity because the gene makeup of the egg can never be the exact copy of either parent donor.
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