Meiosis Notes

 

Definition-

•Cell division by which eggs and sperm are produced.

•The production of sex cells, which are not genetically identical, through a series of cell divisions.

Ensures that humans have the same number of chromosomes in each generation

It is a two-step process that reduces the chromosome number by half—from 46 to 23—to form sperm and egg cells.

This is a reduction in genetic material.

When the sperm and egg cells join at fertilization, each contributes 23 chromosomes so the resulting embryo will have the usual 46

•Interphase: Before meiosis begins, genetic material is duplicated.

•First division of meiosis

–Prophase 1: Duplicated chromatin condenses. Each chromosome consists of two, closely associated sister chromatids. Crossing over can occur during the latter part of this stage.

–Metaphase 1: Homologous chromosomes align at the equatorial plate.

–Anaphase 1: Homologous pairs separate with sister chromatids remaining together.

–Telophase 1: Two daughter cells are formed with each daughter containing only one chromosome of the homologous pair.

•Second division of meiosis: Gamete formation

–Prophase 2: DNA does not replicate.

–Metaphase 2: Chromosomes align at the equatorial plate.

–Anaphase 2: Centromeres divide and sister chromatids migrate separately to each pole.

–Telophase 2: Cell division is complete. Four haploid daughter cells are obtained.

•One parent cell produces four daughter cells. Daughter cells have half the number of chromosomes found in the original parent cell and with crossing over, are genetically different.