Transcript 10.2 Section Objectives – page 263

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.
Homologous Chromosomes
• Each pair of homologous chromosomes has genes for
the same traits.
mom
dad
-same size
-same shape
-same genes located in the same place
Diploid Cells
• A cell with two of each kind of chromosome
is called a diploid cell.
• Also called SOMATIC cells
• All of your body cells are diploid (2n).
• Body cells (diploid) are different from sex cells.
•
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, so
that when the sperm and egg combine- it
will equal 46 Chromosomes.
Haploid Cells
• So, sex cells CANNOT be diploid.
•A cell containing only one of each kind of
chromosome is called a haploid cell (n).
• Also called GAMETES
Sexual Reproduction
Zygote
Diploid and Haploid Cells
Chromosome Numbers of Common Organisms
Organism
Body Cell, Diploid #
Sex Cell, Haploid #
Fruit fly
8
4
Garden pea
14
7
Corn
20
10
Tomato
24
12
26
13
Apple
34
17
Human
46
23
Leopard Frog
Chimpanzee
Dog
Adder’s tongue fern
48
24
78
39
1260
630
In Humans, how many chromosomes would each of
these cells have…..
CHEEK CELL
46
SPERM CELL
23
EGG CELL
23
NERVE CELL
46
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:
It starts with a DIPLOID cell
cell division that makes BODY CELLS.
46
Chromosomes Replicate
92
46
46
It ends with TWO IDENTICAL DIPLOID cells
The kind of cell division that produces sex cells (haploid)
containing half the number of chromosomes as a body cell, is
called meiosis.
Meiosis
I
Meiosis
II
Meiosis:
cell division that makes SEX CELLS.
46
It starts with a DIPLOID cell
Chromosomes Replicate
92
46
23
46
23
23
23
It ends with FOUR HAPLOID cells (NOT identical)
MALE MEIOSIS
Spermatocyte
Diploid
Sperm
(Haploid Gametes)
FEMALE MEIOSIS
Oocyte
Diploid
Eggs / Ova
(Haploid Gametes)
Crossing-Over
During Meiosis:
Homologous chromosomes
actually break and exchange
traits- in a process known as
crossing over.
Takes place during Prophase I
FROM
MOM
This
chromosome
inherited by
mom could code
for straight hair,
brown hair, and
green eyes…
FROM
DAD
After crossing-over
This
chromosome
inherited by dad
could code for
curly hair,
black hair, and
brown eyes…
Now one chromosome
passed on to offspring
could have traits from
both homologous… curly
hair, brown hair, and
green eyes…
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
• These haploid cells are called sex cells- gametes.
• Male gametes are called sperm.
They are created in the male sex gland,
which are testes.
• Female gametes are called eggs.
They are created in the female sex gland,
which are ovaries.
Meiosis
• When a sperm fertilizes an egg, the
resulting zygote once again has the
diploid number of chromosomes.
Zygote = a fertilized egg
Cell division
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.
-Dimples are dominant over no dimples
-Curly hair is dominant over wavy hair
-Wavy hair is dominant over straight hair
- Tongue curling is dominant over no tongue curling
-Hitchhiker thumb is recessive to straight thumb
-Cleft chin is dominant over no cleft chin
-Having anxiety is dominant over not having anxiety