1. KEY CONCEPT During meiosis, diploid cells undergo two cell divisions that result in haploid cells.

2. Haploid cells develop into mature gametes.
Gametogenesis is the production of gametes.
Gametogenesis differs between females and males.
Sperm become streamlined and motile.
Sperm primarily contribute DNA to an embryo.
Eggs contribute DNA, cytoplasm, and organelles to an embryo.
During meiosis, the egg gets most of the contents; the other cells form polar bodies.

3. Cells go through two rounds of division in meiosis.
Meiosis - is the process of forming gametes. It reduces chromosome number from diploid to haploid and creates genetic diversity.
Apply: Why is it important that gametes are haploid?

4. Pairs of homologous chromosomes (homologs) separate in meiosis I.
Meiosis I and meiosis II each have four phases, similar to those in mitosis.
Pairs of homologous chromosomes (homologs) separate in meiosis I.
Homologous chromosomes are similar but not identical. They have the same genes but may code for different variations of a trait.
Sister chromatids separate in meiosis II.
Sister chromatids are copies of the same chromosome. They are genetically identical.
homologous chromosomes
Fig. 2.1 – Homologous chromosomes (shown duplicated) are two separate chromosomes – one inherited from the mother and one from the father.
sister
chromatids
sister
chromatids

5. Meiosis I occurs after DNA has been replicated.
The main event for meiosis I is to separates homologous chromosomes. At this point the cells are still diploid (2n).

6. The main event for meiosis II is to separate sister chromatids
The main event for meiosis II is to separate sister chromatids. This results in 4 genetically unique haploid cells (n).
DNA is not replicated between meiosis I and meiosis II.

7. Meiosis differs from mitosis in significant ways.
Meiosis has two cell divisions while mitosis has one.
In mitosis, homologous chromosomes never pair up.
Meiosis results in haploid cells; mitosis results in diploid cells.
Apply: How many different combinations of chromosomes can result from meiosis in humans? Answer: 223 or 8,388,608