Transcript Meiosis and Mitosis

Mitosis VS Miosis
WARM-UP
HOW MANY CHROMOSOMES ARE FOUND
IN EACH HUMAN BODY CELL?
• In the body cells of animals and most plants,
chromosomes occur in pairs.
• In each pair, you inherited one from your mom, the
other from your dad.
From
Mom
From
Dad
Homologous Chromosomes
• The two chromosomes of a pair are called
homologous chromosomes.
• Each pair of homologous chromosomes has genes for
the same traits.
Diploid Cells
• A cell with two of each kind of chromosome
is called a diploid cell or somatic (body) cells.
• All of your body cells are diploid (2n).
•
Each person can only pass on ONE of their homologous
chromosomes to their young.
HUMANS = 46 CHROMOSOMES
IN THEIR BODY CELLS
Each parent passes 23 to their young.
Sperm(23)+Egg(23)=46 chromosomes
Haploid Cells
A cell containing only one of each kind of
chromosome is called a haploid cell (n).
•Sex cells (gametes) are haploid cells.
Sexual Reproduction
Zygote
Since they have different amounts of chromosomes, they are made in different ways
● Body cells are made by the division process MITOSIS.
● Sex cells are made by the division process MEIOSIS.
Before a cell can divide by either method, it must first prepare for
cell division.
The cell cycle (or entire life cycle of the cell) consists of:
INTERPHASE: The longest/busiest stage in a cell’s life
1. Chromosomes (DNA) replicates
2. Cell grows bigger
NUCLEAR DIVISION: Mitosis or Meiosis
CYTOKINESIS: When the cytoplasm divides and the
cell completely separates.
MITOSIS:
C E LL DI VI SI ON T H AT M A KE S B O DY C E LLS .
It starts with a DIPLOID cell
46
Chromosomes Replicate
92
46
46
It ends with TWO IDENTICAL DIPLOID cells
The cell division process that occurs in haploid cells is called
meiosis.
Meiosis
I
Meiosis
II
MEIOSIS:
C E LL DI VI SI ON T H AT M A KES S E X C E LLS .
46
It starts with a DIPLOID cell
Chromosomes Replicate
92
46
23
46
23
23
23
It ends with FOUR HAPLOID cells (NOT identical)
CROSSING-OVER
During Meiosis:
Homologous chromosomes
actually break and exchange
traits- in a process known as
crossing over.
Takes place during Prophase I
Crossing over can occur at any location on a chromosome, and
it can occur at several locations at the same time.
This causes the traits found in each gamete varied. This is
why siblings of the same parents can look so different from
each other.
Nondisjunction
• The failure of homologous chromosomes to separate
properly during meiosis is called nondisjunction.
•This would occur when homologous chromosomes
are suppose to separate from each other.
Meiosis
• When a sperm fertilizes an egg, the
resulting zygote once again has the
diploid number of chromosomes.
VIDEO
Zygote = a fertilized egg
GET YOUR COMP BOOK
1. PUT IN YOUR MEIOSIS NOTES
2. PREPARE A PAGE FOR
“CROSSING OVER/ GENETIC VARIATION”
In this activity, you will model Crossing over that occurs
during Prophase I of Meiosis and discover how this
small event causes genetic variation in siblings.
1. Take your strip of paper
This will end up being one
homologous pair of
chromosomes.
The six bands will represent
different genes
What are genes?
2. # The bands 1-6 starting at
the top
Write the # of the band on both
sides
3. Color the bands as follows:
1.
2.
3.
4.
5.
6.
Blue
Red
Purple
Green
Brown
Yellow
4. Label the Type of Gene at
the bottom of each band…
1. Dimples
2. Hair Texture
3. Tongue Curl
4. Hitch Hiker Thumb
5. Cleft Chin
6. Anxiety
5. Cut your strip in half long-ways
These two strips represent
Homologous chromosome pair #1
6. For each chromosome, assign
a characteristic that was passed
down for each gene.
For example: In the “Hair Texture”
band you could write
Straight, Curly, or Wavy
Give only 1 characteristic per gene
HOMOLOGOUS CHROMOSOME
PAIR #1
Pretend this
homologous pair is in
either a Spermatocyte
or Oocyte…
and it is time for
Meiosis
During Meiosis
Prophase I
Homologous
Chromosomes break
and exchange genes
(Crossing Over)
7. Cut away two
genes on both
chromosomes and
exchange them
8. Tape up your newly
crossed-over
chromosomes.
This ‘mixes it up’
So your chromosomes
should still have the
same genes in the same
order 1-6, BUT have a
different mix of
characteristics than
before.
During Anaphase your
chromosomes are parted
from each other and are
put in different sex cells.
When one of these sex
cells unites with another
then the new baby will
have a complete set of
homologous
chromosomes.
9. Find someone in
class and trade ONE of
your homologous
chromosomes.
Pretend you and your classmate have
created siblings
(two children from the same parents)
10. Tape/glue your sibling’s homologous
pair #1 in your comp book.
-One chromosome should be yours
-The other chromosome should be
from the other parent.
Answer the questions on the next slide
about crossing over and genetic variation.
ANSWER THESE QUESTIONS IN YOUR
COMP. BOOK:
1. How does Crossing Over create genetic variation?
2. Specifically how were the genes/characteristics different in the siblings
even though they came from the same parents?
3. Why is Crossing over important in Meiosis?
4. Are there any traits that your sibling could possibly pass down to the next
generation that the other sibling could not? EXPLAIN.