Intro to Meiosis

1
Intro to Meiosis
2
Meiosis
What is it? Who does it? Where does it happen?
Why does it happen? Why is a different
process needed?
Making gametes (sperm eggs)
All sexually reproducing organisms
In males- in the testes In females- in the ovaries
To allow organisms to reproduce

1. Chromosome needs to be cut in half
2. Creates genetic diversity (can help evolution of
   species)

3
Meiosis allows sex cells to join to form a
complete set of chromosomes/instructions to make
a new organism.
4
Remember, humans have 23 pairs of chromosomes
Pairs 1-22 are said to be Homologous
chromosomes (they go together because they have
same traits but are not identical)
Gene for eye color
Gene for hair color
5
Now lets look at how sex cells are made
6

• Eight Stages of Meiosis
• Prophase I
• Metaphase I
• Anaphase I
• Telophase I
• Prophase II
• Metaphase II
• Anaphase II
• Telophase II

7
Prophase I 1.) Homologous chromosomes pair
up 2.) Crossing over occurs between replicated
homologous chromosomes
Crossing over (exchanging parts)
8
Crossing over
9
Note chromosomes in daughter cells are all
different
10
Metaphase I Homologous chromosomes get next to
each other in the cell, and line up in
pairs Along the middle of the cell.
Question How is metaphase I of
meiosis different from metaphase of mitosis?
Note Xs are next to each other,
not above each other
11
Anaphase I homologous chromosomes separate
12
Telophase I sister chromatids still need to
be separated
still looks like an X
13
Now Meiosis II occurs (looks like
mitosis)
14
Meiosis
15
Meiosis animation
16
Practice

• 1.) If a haploid cell has 7 chromosomes, how many
  chromosomes does a diploid cell have?

17
(No Transcript)
18

• 2.) If a gamete has 23 chromosomes, how many
  chromosomes are in a body cell of that organism?

19

• 3.) How are the cells at the end of meiosis I
  different from the cells at the end of meiosis
  II?

20

• 4.) What is the same and what is different about
  mitosis and meiosis?

21

• 5.)Why is crossing over important to the survival
  of a species?

22
And now lets see a more technical version
http//www.pbs.org/wgbh/nova/baby/divi_flash.html
Meiosis technical
23

• http//www.sumanasinc.com/webcontent/animations/co
  ntent/meiosis.html

24
One final detail
25
The End!