Meiosis

1
Meiosis
Section 11-4
Box 40
Box 48

• Humans have 46 chromosomes in every cell of our
  bodies except the sex cells or gametes (eggs and
  sperm)- they have 23 chromosomes
• When a baby is conceived, an egg from mom and a
  sperm from dad, combine into the first cell of
  the new baby. 2323 46

Box 49
Box 40
Box 50
46
What would happen if the egg and sperm both had
46 chromosomes?
Baby would have 92 chromosomes!! Disaster!
92 chromosomes
death, disease
2
Remembering Meiosis
Box 51

• Mitosis is a process that occurs in almost every
  cell of your body (body cells), except the sex
  cells, or gametes.
• Mitosis My toe sis, it happens in your toes!
• Meiosis is a process of cell division that
  doesnt happen in your toes, it only happens in
  your sex cells, gametes
• Meiosis My OH! Sis (as in uh-oh!)

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Box 52
3
Meiosis

• To solve this problem, the cells in the gametes
  (eggs and sperm), undergo Meiosis instead of
  Mitosis, when they divide.
• Why Meiosis?
• Most cells in our body are Diploid (di 2)
• Diploid have 2 sets of chromosomes, 2n (one
  from mom, one from dad)
• Sex cells, or gametes, are Haploid
• Haploid have 1 set of chromosomes, 1n

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4
Chromosome Number

• An example.
• Fruit Flies (Drosophila), have 8 chromosomes
  total 4 from dad fruit fly, 4 from mom fruit
  fly.

Box 43
2n 8
Diploid number?
Haploid number?
1n 4
5
Phases of Meiosis
Homologous same chromosome, it just comes from
different parents (mom or dad)

• How are haploid (1n) gamete cells produced from
  diploid (2n) cells?
• By Meiosis (my-OH-sis)
• Meiosis process of reduction cell division
  where the of chromosomes per cell is cut in ½
  by the separation of homologous chromosomes

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Box 45
Box 58
Box 46

• Meiosis involves 2 distinct divisions,
• Meiosis I
• Meiosis II
• Results of Meiosis? cells with a haploid (1n)
  number of chromosomes

Box 59
6
Meiosis I
Interphase I
Prophase I
Chromosome duplication
7
During prophase I of Meiosis, when the tetrads
form, a phenomenon called Crossing Over can
occur.
You got chocolate in my peanut butter!
You got peanut butter in my chocolate!
Sorry!
Hey hot stuff, wanna dance?
Owww! My arm!
Who me?
I think he likes me!
Help!
8
Meiosis I
Interphase I
Prophase I
Metaphase I
Anaphase I
9
Meiosis I
Interphase I
Prophase I
Metaphase I
Anaphase I
Telophase and Cytokinesis
10
Meiosis II
The 2 new cells now enter a 2nd round of meiotic
division
No more chromosome duplication
prophase II
11
Meiosis II
prophase II
metaphase II
Prophase II of meiosis I results in 2 haploid
daughter cells, each with ½ the of chromosomes
as the original cell
12
Meiosis II
4
3
anaphase II
telophase II
prophase II
metaphase II
2
1
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Flow Chart for Meiosis
I
P
Interphase I
M
Prophase I
A
Metaphase I
Anaphase I
T
92
Telophase I Cytokinesis
92
92
92
Humans 2n 46
46
P
Prophase II
M
A
T
Telophase II Cytokinesis
Anaphase II
Metaphase II
46
46
46
23
4 daughter cells with haploid (1n)
I then PMAT..PMAT
14
Gamete Formation

• Why do we even have Meiosis?
• To make gametes (eggs and sperm).
• Male gametes sperm
• Female gametes eggs

Box 71
Skip Box 59
Why do we need eggs and sperm?
End of Chapter 10 and Chapter 11 Section 11-4