During meiosis in animal cells, haploid gametes are formed. Genetic diversity is critically important in gamete formation to ensure different genetic combinations are made during reproduction. Meiosis maintains genetic diversity through crossing over and independent assortment. Crossing over occurs during prophase I and is the physical exchange of genetic material between homologous chromosomes. Crossing over occurs at the chiasma and is facilitated by double stranded breaks and recombinase enzymes. Independent assortment is the separate segregation of homologs during meiosis; namely that each homolog segregates free of other pairs. The independent nature of this segregation allows a greater variety of genetic recombinations in gametes. Both crossing over and independent assortment allow for the production of genetically diverse gametes and therefore genetically diverse organisms.

The processes of mitosis and meiosis have many differences between them. These differences include the genetic recombination event called crossing over unique to meiosis, the fact that only mitotic daughter cells are genetically identical to parent cells, and the paring of homologous chromosome pairs during metaphase I of meiosis. One characteristic that is common to both processes is that they occur in all animals.

During prophase I of meiosis, a crossing over event allows for genetic recombination. Crossing over ensures the formation of gametes with different genetic combinations. The process involves the swapping of genetic material from one homologous chromosome pair to another, and is facilitated by double stranded breaks in the DNA helix and recombinase enzymes. The structure formed during crossing over is called the “Holliday junction”.

During meiosis, the “chiasma” is the point of chromatid contact that precedes crossing over. The crossing over event then occurs at this point. Synapsis refers to the pairing of homologs during prophase I of meiosis.

During the anaphase I stage of meiosis, homologous chromosome pairs separate to opposite poles of the cell, and the cell elongates. The sister chromatids remain attached at the centromeres. This maintenance of sister chromatids is the key difference between meiosis and mitosis. In mitosis, anaphase features the separation of sister chromatids, which is what will happen during anaphase II of meiosis. Note however, that the sister chromatids in meiosis are not identical, due to crossing over in prophase I. 

Meiosis is the process that forms haploid gametes, or sex cells, that will go on to form zygotes after fertilization. Meiosis is performed by germ line cells, which, in humans, are located in the gonads (ovaries of females and in the testicles of males).

Meiosis produces four daughter cells that are haploid, meaning that they contain half the number of chromosomes as the parent cell. Human parent somatic cells have 46 chromosomes, or 23 chromosome pairs, meaning that gametes produced during meiosis have 23 chromosomes.

Synapsis is the pairing of homologous chromosomes during prophase I of meiosis. Due to synapsis, pairs of homologous chromosomes are arranged in a way that allows for crossing over to occur, which leads to genetic recombination, and genetic diversity.

Meiosis I is the first cell division of the entire meiosis process. Following segregation of homologous chromosome pairs, or tetrads, the two resulting daughter cells have half the number of chromosomes as the parent cell. These chromosomes have two sister chromatids per chromosome, which are nonidentical due to crossing over.

Prophase II marks the beginning of the second cell division of meiosis, called meiosis II. Unlike prophase I, the chromosomes are not duplicated prior to the start of prophase II. However, during prophase II, the centrioles replicate, resulting in two pairs of centrioles per cell. The two centriole pairs separate to opposite cell poles. Other features of prophase II are chromosome condensation, the degradation of the nuclear membrane, and meiotic spindle formation.