How to pass everything

Topics: Chromosome, Meiosis, DNA Pages: 1 (341 words) Published: August 24, 2014
The differences have come through, in part, because of the genetic variations that occur via meiosis. When single cell organisms were the dominate life on the planet the method of reproduction was mitosis which creates identical replicas of the parent cell’s genetic material. This was and still is accomplished through asexual reproduction. With sexual reproduction however, varying arrangements of homologous chromosomes at the metaphase of meiosis I affect the resulting gametes (Simon, Dickey, & Reece, 2013). The side by side orientation of each homologous pair of chromosomes found in meiosis is a matter of chance (Simon et al., 2013). The more chromosomes that a species has the more random variations can come about (Simon et al., 2013). For any species the total number of chromosome combinations that can appear in gametes is 2n, where n is the haploid number (Simon et al., 2013). Humans have 23 haploid chromosomes, so for humans, the possible chromosome combinations is 223, or around 8 million possible combinations (Simon et al., 2013). This is varied exponentially further through sexual reproduction. Since a human egg cell and sperm cell both have around 8 million possible combinations we need to multiple these numbers to achieve the total number of possible chromosome variations (Simon et al., 2013). The total number then of all possible variations of a human diploid zygote is roughly 64 trillion (Simon et al., 2013). Also, corresponding segments between nonsister chromatids of homologous chromosomes occur during the prophase I of meiosis (Simon et al., 2013). This crossing over of chromosomes further increases the variations possible in the resulting gametes (Simon et al., 2013). These chromosomes are called recombinant because they result from genetic recombination, or the mixing of gene combinations that are different from those carried by parental chromosomes (Simon et al., 2013). Since most chromosomes have thousands of genes, a single crossover event can...
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