Chapter 3.2 What is meiosis?

Sex cells Sperm cells are male reproductive cell. Eggs are female reproductive cell.

What is gamete? Gamete- is a reproductive or sex cell. It can mean either a sperm cell or an egg cell. Reproduction means making a baby.

Inheritance of chromosomes: 23 chromosomes in a sperm cell 23 chromosomes in an egg cell 46 chromosomes in a baby

Diploid vs. Haploid Haploid- means a cell that contains only a single set of chromosomes (23 chromosomes) and therefore only a single set of genes. It’s only possible in sex cells (sperm and egg cells).

Diploid vs. Haploid Diploid- means a cell that contains both sets of homologous chromosomes meaning: 23+23= 46 chromosomes (in any cell: cheek cells, brain cells, heart cells except for sex cells).

Body cells vs. gametes Organism Body cells Gametes (sperm or eggs) Fruit fly 8 (diploid number of chromosomes) 4 (haploid number of chromosomes) Bull frog 26 13 Human 46 23

MEIOSIS Gametes (sperm or eggs) are produced during a special process called MEIOSIS. It’s division of one cell (46 chromosomes) into four cells (23 chromosomes). The number of chromosomes is cut in half. Each gamete has only a half of number of chromosomes. MEIOSIS-produces 4 genetically different haploid sex cells.

MEIOSIS Meiosis—the process happens in two parts- meiosis I and meiosis II. It has a cross-over that results in exchanging DNA between two chromosomes.

Cross-over in meiosis

Mitosis vs. Meiosis Mitosis results in the production of two genetically identical diploid cells, whereas meiosis produces four genetically different haploid sex cells.

Checking concepts: 1. Describe the main results of meiosis.

How many human chromosomes does a human egg cell have? Explain.

What would happen if the chromosomes did not move to the opposite sides of the nucleus before the cell pinched apart?

Why is it important for gametes to have half number of chromosomes?

What are the principal differences between mitosis and meiosis?

What do the terms diploid and haploid means?

Critical Thinking: In human cells, 2N = 46 Critical Thinking: In human cells, 2N = 46. How many chromosomes would you expect to find in a sperm cell? In an egg? In a white blood cell? Explain.

A frog has 26 chromosomes in cells A frog has 26 chromosomes in cells. What is the number of chromosomes in the frog’s gametes?

Fill in blanks: All human body cells contain ______ chromosomes. Sperm cells and egg cells are ________________________. The process that reduces the number of chromosomes in a cell by one-half is _____________. Meiosis occur only in the formation of _____________.