Sexual reproduction
From EvoWiki
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Sexual reproduction is a reproductive strategy used by some organisms in which genetic material from two different individuals contribute DNA to offspring. This reproductive strategy can be compared to reproduction in which all of the DNA of new individual members of a species is derived from a single parental organism. Sexual reproduction requires a mechanism for combining the DNA from two individuals. A key restriction on such combining of DNA is that there has to be a means of preventing the doubling of DNA in cells with each generation. The solution to this problem is a special type of cell division called meiosis. During meiosis, haploid gametes, or sex cells are produced that have half of the number of chromosomes found in the organism's diploid cells. When the DNA from two different gametes is combined, a diploid zygote is produced that can develop into a new individual.
The evolutionary advantage from sexual reproduction is largely due to special alterations in chromosomes that happen during meiosis. During the first meiotic cell division, homologous copies of chromosomes align and exchange pieces in a process known as crossing over. This allows new combinations of genes to form on chromosomes. In particular, mutated and damaged genes can be removed from the chromosomes that will be passed on to viable offspring.
