Synapsis allows crossing over between homologous chromosomes. Pairing is called synapsis.Ĭrossover exchanges between homologous chromosomes is rare. Homologous chromosomes pair during prophase l. Similar or homologous chromosomes do not pair. There are several key differences between meiosis and mitosis that are summarized in the following table: The key events that happen in each of the stages of meiosis are summarized Mitosis Passing on a complete set of human genes requires one chromosome from each pair to end up in each gamete. The exception to this would be the sex (X and Y) chromosomes. Homologous chromosomes have the same genes although in heterozygous people the genes would be different alleles (A,a). One chromosome from each pair came from the male parent, the other from the female. Homologous chromosomes: The 46 chromosomes in a somatic cell can be arranged into 23 homologous or similar pairs. Therefore, human gametes are haploid (one set). One set of chromosomes came from each parent when their gametes fused. You are a diploid organism ('di' means two and 'ploid' means sets). To appreciate meiosis and gamete formation it is important to first understand two ideas, chromosome sets and homologous chromosomes.Ĭhromosome sets: The 46 chromosomes you have consist of two sets. Meiosis occurs in specialized cells of the body called germline cells. In our human bodies, the four gametes will each have 23 chromosomes which means the 46 chromosomes in the somatic cell must replicate during interphase prior to meiosis just as they would before mitosis. The four cells each have half the chromosome number found in the somatic cell. The objective of meiosis is to make four cells from a single somatic cell.
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