Download Meiosis and Variation Guided Notes

MEIOSIS
Sexual Reproduction
Somatic cells vs. Gametes
Our bodies have 2 different types of cells
⬜
Somatic cells
◼
◼
Component of body
tissue.
Example:
⬜
Gametes
◼
sexual reproduction.
◼ Example:
▫ sperm cell and egg cell.
▫ muscle, bone, skin, nerve,
heart and brain.
◼
◼
46 chromosomes
▫ 23 pairs
End product of Mitosis
Sex cells; involved in
◼
23 chromosomes
▫ (No pairs)
◼
End product of Meiosis
◼ Sperm + egg (fertilized) =
zygote
Gamete (23) + Gamete (23) =
Zygote (46)
HOW DO WE MAKE
GAMETES?
We need to produce cells with ½ the
amount of chromosomes (23).
We do that through Meiosis!
⬜
Draw these Homologous Chromosomes
◼
◼
Label the chromosome from Dad and the chromosome
from Mom
Color the banded genes on each chromosome.
▫ These bands represent different versions of the same gene
(trait)
Why is genetic diversity a good thing?
⬜ Sexual Reproduction = Variety
⬜
Why?
◼
◼
⬜
!
Why don’t your siblings look EXACTLY like you?
Why don’t you look EXACTLY like your parents?
Let’s talk about 3 sources of Variety in Sexual
Reproduction.
1. Crossing Over increases Variety
• Occurs during Meiosis I
• Homologous chromosomes form
tetrads (they find their pair) in
Prophase I.
• While in tetrads, chromosomes
exchange genetic material to make
new combinations.
(Recombination)
2. Independent Assortment increases Variety
⬜ Independent Assortment :
Homologous pairs can line up in
2 ways:
⬜
Mom’s chromosome on left or
Dad’s chromosome on left.
⬜
⬜
⬜
This produces different genetic
combinations in the daughter
cells.
⬜
In humans 223 = 8 million
combinations!
IS THIS ENOUGH
Variety?
3. Random Fertilization increases Variety
•
Any sperm can fertilize any egg.
•
Dad has 8 million different
genetic variations in sperm.
•
Mom has 8 million different
genetic variations in eggs.
•
8 million x 8 million =
64 trillion possible babies
•
Crossing over squares that number!
64 trillion squared = 27 zeros!!
4,000,000,000,000,000,000,000,000,000
Twins
⬜
What are fraternal twins?
◼
⬜
Two fertilized eggs
What are identical twins?
◼
A single zygote that splits in
two or three or..