Meiosis and Fertilizationmy-OH-sis

Meiosis is cell division used for:• Producing gametes (sex cells)

What is Meiosis?

***Makes 4 different cells!***

•Part of it looks like mitosis!

Meiosis

• DNA replicates once, cell divides twice

• Creates haploid (n) sex cells

• In humans, takes place in ovaries and testes

Meiosis

Prophase 1

• Chromosomes become visible and the nuclear membrane breaks apart

• Crossing over occurs!

• Creates new gene combinations!

Metaphase 1 vs. 2

• Metaphase 1- homologous chromosomes pair up in the middle

• Metaphase 2- single chromosomes line up in the middle

Anaphase 1 vs. 2

• Anaphase 1- homologous chromosomes separate and move apart

• Anaphase 2- Chromatids separate and move apart

Telophase 1 vs. 2

• Telophase 1- Single cell splits into 2 cells, goes right into Prophase 2

• Telophase 2- Two cells each split, creating 4 haploid cells

Meiosis: A

Second Look

• Meiosis results in 4 genetically different haploid daughter cells

One major point!

*These cells are sperm and eggs!

Fertilization

n n+ = 2n

Haploid Egg cell

23 chromosomes

Haploid Sperm cell

23 chromosomes

DiploidZygote

46 chromosomes

Homework Review

1. Describe the main results of meiosis.

2. What are the principal differences between mitosis and meiosis?

3. What do the terms diploid and haploid mean?

4. What is crossing-over?

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