Master Prophase with Picmonic for Pre-Health

Centrioles are groups of microtubules that, in both types of cell division, migrate to different poles and attach to chromosomes.

A spindle apparatus is fundamentally comprised of spindle microtubules and hundreds of proteins that, in both types of cell division, help separate chromosomes during cell division.

In the Prophase stage of Meiosis I, the cell starts out as diploid. Meiosis is a type of cell division that is necessary for sexual reproduction, and begins with diploid germ cells.

In Meiosis I Prophase, homologous chromosomes are paired together. Homologous chromosomes are two pairs of sister chromatids that code the same set of genetic information but have different alleles. This is because one copy comes from the mother, while another copy comes from the father. Two homologous chromosomes closely associated is called a tetrad, because there are four chromatids.

Crossing over is the process whereby homologous chromosomes, in a tetrad formation, exchange equivalent nucleotide sequences. Keep in mind that sister chromatids on the same chromosome do not exchange sequences because two sister chromatids are genetically identical prior to any crossing over occuring. It only occurs between two adjacent homologous chromosomes.

In Meiosis II Prophase, the cell is haploid. This is because in meiosis I, homologous chromosomes were lined up such that each new cell got either mom's chromosome or dad's chromosome for each of the 23 chromosomes. Thus, the new cells have a mix of genetic information from both parents, but only have 1 allele for each gene.

In Mitosis Prophase, the cell is diploid. This is the case in humans, where most human cells are diploid other than gametes and undifferentiated stem cells. The goal of mitosis is to produce two identical daughter cells.

Sister chromatid pairs stay separated in meiosis II and mitosis. In meiosis II, the homologous chromosomes have already been separated so tetrads cannot form. In mitosis, tetrads can form but do NOT form because the goal is to produce genetically identical daughter cells that have a copy of DNA from both original parents of the dividing cell.