Set up today’s page for Cornell Notes Page: 39 Date: Title: Meiosis Essential Question: How is meiosis related to the cell cycle?

1. What are Chromosomes?

CHROMOSOMES: coiled DNA located in the nucleus Organisms inherits one of each numbered chromosome from each parent. HOMOLOGOUS CHROMOSOMES: a matching pair of chromosomes

Before After A KARYOTYPE is a picture of a person's chromosomes. The chromosomes are isolated, stained, examined under a microscope, and a picture is taken. Then the picture is cut up and the chromosomes are lined up in homologous pairs from largest to smallest. A trained cytogeneticist can look for problems or mutations in the chromosomes.

DIPLOID: cell that contains 2 sets of chromosomes *Somatic (body) cells are diploid n = the number of chromosomes *two sets of “red, blue, yellow”

Most mammals are diploid organisms…including you!! Humans: 46 (23 pairs) Gorilla: 48 (24 pairs)Elephant: 56 (28 pairs) Coyote: 78 (39 pairs) Goat: 60 (30 pairs)

2. Sexual Reproduction & Our Cells

Biologically speaking, what’s the point of sex?

FERTILIZATION: 2 gametes combining their DNA GAMETES: sex cells Males = sperm Females = egg

If YOU are human, then YOUR cells have 46 chromosomes and your parents’ cells each have 46 chromosomes. Agreed? So if you get DNA from both your parents, then why don’t you end up with 92 chromosomes? Aaron: It’s because the male gamete actually only contributes 35 of the chromosomes and the female gamete contributes the remaining 11 Brittney: When the male and female gamete join, the result is 92 chromosomes but as the baby develops, chromosomes that are not needed are destroyed during mitosis. Karen: There must be some way that the male and female gamete each carry only 23 of the chromosomes from each parent so that when they get together they equal 46. Blake: The gametes each contain the full 46 chromosomes from each parent but when fertilization occurs only the first 23 that pair up are used.

When gametes (sex cells) are formed, a process occurs that separates the two sets of genes so that each gamete ends up with just one set. Karen: There must be some way that the male and female gamete each carry only 23 of the chromosomes from each parent so that when they get together they equal 46.

HAPLOID: cells that contain only 1 set of chromosomes *Gametes are haploid

3. Meiosis

MEIOSIS involves TWO cell divisions that result in FOUR haploid gametes. ** Meiosis is how gametes are produced** 1. 2.

Mom’s chromosome Dad’s chromosome Identical Copy MITOSIS

CROSSING OVER: pieces of the maternal and paternal chromosomes are exchanged during meiosis **results in genetic variation** Dad’s chromosome Mom’s chromosome Crossing Over DNA Replication Crossing Over

The diagram below shows the possible variations for just one chromosome pair going through meiosis. Imagine the possibilities you could get with 46!!!