Meiosis

1
Meiosis

• Making Gametes

2
Mitosis Review
Mitosis Division of the Nucleus
Prophase
Metaphase
Anaphase
Telophase
How many times does the nucleus divide in mitosis?
ONE
3
Mitosis Review
Slide 2

• Think in your head
• What are the four stages of mitosis?
• What is the purpose of mitosis?

Prophase Metaphase-Anaphase-Telophase
The first purpose of mitosis is growth. The
second function of mitosis is repair. Cells are
constantly wearing out and getting damaged and
unless an organism replaces them at least as fast
as they are lost, a gradual deterioration will
occur.
4
Meiosis

• Making Gametes

5
Introductory Vocabulary
Slide 3

• 1. Somatic cell body cell
• a. EX skin or bone cell
• 2. Diploid two sets of chromosomes 2n
• a. EX humans have 2 sets of chromosomes
  in each body cell 1 set came from the
  sperm the other set came from the egg

Diploid (2n) somatic cell
Mitosis results in 2 diploid cells
6
About Meiosis
Slide 9

• 1. Purpose of meiosis produce haploid gametes.
• 2. Haploid having 1 set of chromosomes 1n
• 3. Gametes- special cells used in sexual
  reproduction.
• a. EX egg and sperm cells
• b. Gametes are ONLY produced by meiosis
• 4. Meiosis occurs in reproductive organs

7
Overview of Meiosis
Slide 10

• 1. Interphase cell duplicates its chromosomes
• 2. Chromosomes are only duplicated ONCE
• 3. Cell divides 2 times to produce genetically
  different 4 cells

8
Stages of Meiosis I
Slide 11
9
Prophase I
Slide 12

• 1. Chromatids pair up with their Homologous pair
  forming a tetrad.
• 2. Crossing over is a process where pieces of
  two homologous chromosomes switch places.

10
Replicated Chromosome
Slide 13
Sister Chromatid
Sister Chromatid
11
Tetrad
Slide 14
Maternal chromosome replicated
Paternal chromosome replicated
12
Crossing Over Occurs in Prophase I
Slide 15

• 1. Homologous chromosomes
• a. Pair up alongside each other lengthwise
• b. Swap bits and pieces of their chromosomes,
  shuffling the genome
• 2. Crossing over ONLY happens in Prophase I
  results in NEW chromosomes that did not exist
  before in either parent
• 3. Why crossing over is important
• a. It creates the genetic diversity of ALL
  sexually reproducing organisms
• b. Yes, this means you too!

13
Metaphase I Tetrads line up in center
Slide 16
14
Anaphase I Tetrads split
Slide 17
15
Telophase I
Slide 18
16
Stages of Meiosis II
Slide 19
17
Prophase II Chromatid pairs move to center
Slide 20
18
Metaphase II The chromatids line up at center of
the cell
Slide 21
19
Anaphase II chromatid pairs splitTelophase II
cells divide, producing 4 haploid cells
Slide 23
20
Meiosis occurs in the testes and is called
spermatogenesis and in the ovaries of female and
is called oogenesis.