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

2. Vocabulary Words for section 6.2 These words are highlighted in red.
Gametogenesis
Sperm
Egg
Polar body
Crossing over
Genetic linkage

4. Cells go through two rounds of division in meiosis.
Meiosis reduces chromosome number and creates genetic diversity.

5. Haploid cells develop into mature gametes.
Gametogenesis is the production of gametes.
Gametogenesis differs between females and males.
Sperm, the male gamete, is much smaller than the egg cell
Sperm primarily contribute DNA to an embryo.
Eggs, the female gamete, contribute DNA, cytoplasm, and organelles to an embryo.
Polar bodies are cells with little more than DNA that are eventually broken down

6. Pairs of homologous chromosomes separate in meiosis I.
Meiosis I and meiosis II each have four phases, similar to those in mitosis.
Pairs of homologous chromosomes separate in meiosis I.
Homologous chromosomes are similar but not identical.
Sister chromatids divide in meiosis II.
Sister chromatids are copies of the same chromosome.
homologous chromosomes
sister
chromatids

7. Meiosis I occurs after DNA has been replicated.
Meiosis I divides homologous chromosomes in four phases.

8. Meiosis II divides sister chromatids in four phases.
DNA is not replicated between meiosis I and meiosis II.

9. Sexual reproduction creates unique combinations of genes.
Through independent assortment of chromosomes in meiosis
Through random fertilization of gametes
Unique phenotypes may give a reproductive advantage to some organisms.

10. Crossing over during meiosis increases genetic diversity.
Crossing over is the exchange of chromosome segments between homologous chromosomes.
occurs during prophase I of meiosis I
results in new combinations of genes

11. Chromosomes contain many genes.
The farther apart two genes are located on a chromosome, the more likely they are to be separated by crossing over.
Genes located close together on a chromosome tend to be inherited together, which is called genetic linkage.
Genetic linkage allows the distance between two genes to be calculated.

12. MEIOSIS ANIMATION

13. Genetic Variation Among Offspring
Assortment of Chromosomes
How c-somes in each tetrad line up and separate during metaphase I is a matter of chance
Like flipping a coin
The number of combinations possible can be calculated by 2n n=haploid #
HUMANS = 223 = 8 million different combinations solely based on how they line up
Genetic Recombination
New combination of genetic information in a gamete as a result of crossing over during prophase I (which exponentially adds to the possible combinations)