<span>Meiosis occurs in germ cells to produce haploid progeny. Prior to meiosis the genome duplicates so at the start of meiosis you have two copies of each allele. Each chromosome (which is one allele) is paired with its copy. These pairs are referred to as sister chromatids. The sister chromatids are then paired with the other matching chromosome during metaphase.
During meiosis I, the alleles (chromosomes are separated into different cells). This separation occurs during anaphase of meiosis I.
The sister chromatids (which are copies of one allele) are later separated in meiosis II.</span>
When two organisms are found in the same niche they can not generally coexist in the long term. But it is possible that one of the two organisms adapts to the lifestyle of the second organism, or one of the two organisms disappears (by extinction or by migration).
