Thus, we call this the reductional, or Meiosis I division. The offspring from meiosis have half the number of chromosomes as their parent cell, because they receive just one copy of each chromosome, rather than two. An important additional feature of meiosis is the process of recombination, or genetic exchange between the homologous chromosomes. This is indicated by the swapping of red and blue on the homologous chromosomes in the diagram. Although homologous chromosomes contain the same genes, they may have different versions, or alleles, of each gene.
Recombination allows the different versions to be shuffled into new combinations.
And, the physcial mechanism of recombination is required for the chromosomes to segregate properly in the Meiosis I division. Thus, the offspring receives one copy of each chromosome from each parent. Depending upon the recombination events that occurred to produce each gamete, genetic information may be rearranged. This explains why siblings get different combinations of genes from their parents, which is why they look related, but not identical. Any defects in the careful choreography of meiosis can therefore have profound effects on the health of the gametes and the resulting zygotes.