Aim: How are sex
cells created?
Homework:
Castle learning &
Textbook due
FRIDAY
DO NOW: The diagram below includes
information on asexual reproduction.
Asexual
Reproduction
Binary
Fission
Ameba
Budding
Hydra
X
Bread
Mold
Vegetative
Propagation
Potato
Which term belongs in the are labeled X?
a. Graphing
c. Cutting
b. Regeneration
d. Sporulation
How many chromosomes will be found in each of the
two new cells formed as a result of mitotic cell division?
1. Only one-half as many chromosomes as the
parent cell
2. Twice as many chromosomes as the parent
cell
3. Three times as many chromosomes as the
parent cell
4. The same number as chromosomes as the
parent cell
The diagram below represents a microscopic structure
observed during cell division
What part of the structure are indicated by
arrows A, B and C respectively?
Chromosome
B
Centromere
A
C
Chromotid
Fusion (joining) of
gametes (sex cells) to create an
new individual.
There are two parents and two
sets of chromosomes.
Offspring inherit traits from
both parent
Male sex cell  Sperm
Female Sex cell Ovum (egg)
Gametes have only 23 chromosomes. This is
only half of the number of the parent cell.
Fertilization: the sperm chromosomes join the
egg chromosomes.
Together, sperm and egg make a full set of
chromosomes.
•A.K.A. Gametes
•Examples: human egg and sperm cells
•Function is to fertilize
•Used to carry out sexual reproduction
23 chromosomes each
•Have _____
MEIOSIS
Created by the process of __________
DIPLOID: A cell that has a full set of
chromosomes .
(Ex.) Somatic cells (body cells)
HAPLOID: A cell that has only half the
number of chromosomes.
(Ex.) Gametes (egg and sperm)
Compared to the number of CHROMOSOMES in
a normal human body cell, the number in a
normal sperm cell is:
1.
2.
3.
4.
The same
Twice as great
Half as great
Four times as great
How many chromosomes will be found in each of the
two new cells formed as a result of mitotic cell division?
1. Only one-half as many chromosomes as the
parent cell
2. Twice as many chromosomes as the parent
cell
3. Three times as many chromosomes as the
parent cell
4. The same number as chromosomes as the
parent cell
DO NOW:
How does
mitosis effect
chromosome
number?
Why such a large
number?
Remember this
Is when
chromosomes
replicate!
Example:
Human
chromosome
number is
46
____
Each body cell of a chimpanzee contains 48
chromosomes. How many chromosomes
would normally be present in a gamete
produced by this chimpanzee?
1.
2.
3.
4.
24
36
48
96
Pairs of chromosomes that have genes for
the same traits in the same order
Chromatid
Meiosis: is a process that
produces gametes.
o Gametes that have half the
number of chromosomes.
o Separates these
homologous chromosomes
•Meiosis is the type of cell division by
which gamete cells (eggs and sperm) are
produced.
•Meiosis involves a reduction in the
amount of genetic material.
•A.K.A. reduction division
To maintain normal chromosome number
once fertilization occurs
23
23
46
START
46
2n = ____
Called the Diploid #
END
23
n = ____
Called the Haploid #
Meiosis consists of two successive nuclear
divisions with only one round of DNA
replication.
46
Parent cell
92
46
23
46
23
23
23
4 Daughter
cells
Meiosis I
•Interphase
•Prophase
•Metaphase
•Anaphase
•Telophase
Meiosis II
•Prophase II
•Metaphase II
•Anaphase II
•Telophase II
To reduce chromosome number
Gametogenisis
Is the development of mature sex cells called
GAMETES
Formation involves meiosis in immature sex
cells.
2 types:
Spermatogenesis and Oogenesis
Gametogenesis
After meiosis 4 gamete (sex cells sperm)
are produced.
Oogenisis
During this step only one viable gamete (sex
cell egg) is produced and 3 polar bodies.
Genetic Diversity takes place during
fertilization.
This is because 23 chromosomes from
each gamete are combined during this
step!
n
n
2n
n
Mother cell
n
GAMETES
E. Crossing Over
•The exchange of genetic material between
Paternal and Maternal chromosomes
•Important for genetic variation
Which process produces cells with
more genetic diversity, mitosis or
meiosis? Why?
•Answer: Meiosis
•Mitosis produces daughter cells that are
identical to the mother cells
•Meiosis produces daughter cells that are
genetically different from the paternal cells
•So, there is more diversity (difference) in meiosis
Mitosis Vs. Meiosis
F. Mitosis Vs. Meiosis:
Mitosis
2 daughter cells
Identical to parent
46 chromosomes
Somatic cells
(body cells)
Diploid cells (full set of
chromosomes)
Meiosis
4 daughter cells
Different from parent
23 Chromosomes
Gametes
(sex cells)
Haploid cells
(half the # of
chromosomes)
Homologous pairs of chromosomes are NOT normally
found in
1.
2.
3.
4.
Zygotes
Body tissue cells
Gametes
Embryonic nerve cells
Meiosis consists of two successive nuclear
divisions with only one round of DNA
replication.
46
Parent cell
92
46
23
46
23
23
23
4 Daughter
cells
Label the phases shown (1-3)
2
1
3