There are two major parts of the meiosis nuclear division cycle that result in four unique gametes at the end. The first part happens during meiosis one and is called ‘crossing over’, this is when a pair of homologous chromosomes “wrap around” each other and swap equal parts of chromatid material between them. A portion of the chromatid is called a gene, a gene is the part of the chromosome that is responsible for the various traits that can be inherited, it is made of a unique order, number and type of base pair nucleotides, which means it codes for a specific enzyme which is responsible for the trait that is expressed – different forms of the same gene are called alleles,
A gene codes for a specific trait, and a allele allows for variation within that trait e.g. Brown and blue eyes.
Because the pairs of chromosomes are homologous, which means one chromosome of one pair is paternal and the other is maternal and both pairs are exactly the same in terms of genes but may be complete polar differences in terms of specific alleles, so when equal parts swap, certain traits are swapped over. This means that two completely new homologous chromosomes are made which are completely different from both original pairs – a kind of hybrid of both pairs. Because of this more or less random way of recombination, it is made sure that every time crossing over occurs it results in nearly unique homologous chromosomes, this means that two siblings of the same biological parents can