CHECK/TAKE UP
HOMEWORK
SEXUAL REPRODUCTION
CONTINUED
Spermatogenesis and Oogenesis
CELL DIVISION:
A COMPARISON
Mitosis
Meiosis
to produce somatic cells
to produce sex cells
Genetic
Variability
None
Yes - crossing over during
Prophase I
Number of
Divisions
One
Two
Number of Cells
Produced
Two
Four
Number of
Chromosomes Per
Cell
46
Diploid
2n
23
Haploid
n
Function of
Process
GAMETE FORMATION
(GAMETOGENESIS)
•
Meiosis takes place in the testes and ovaries (haploid
sperm [n] and egg cells [n] respectively are produced)
•
Haploid gametes unite to form diploid (2n) zygote
known as fertilization
OOGENESIS
•Begins with a diploid cell called an
oogonium
• Cytoplasm of female gametes doesn’t divide equally
Did you know.....
after
nuclear
division
Before birth, the oogonia
reproduce by mitosis, and
• One daughter cell receives most of the cytoplasm after
they begin meiosis, but stop
the
division.
That
cell
continues
through
meiosis
I
and
at prophase I. Meiosis I will
II continue
to form ONE
viable
egg. This cell contains a large
for one
cell each
quantity
of nutrients
that will support a zygote after
month beginning
at puberty
fertilization
•
The other 3 polar bodies die and the body absorbs the
nutrients.
SPERMATOGENESIS
•
Begins with diploid cell called spermatogonium
•
Equal division of cytoplasm with sperm
•
4 cells produced via meiosis
•
Capable of many mitotic divisions before meiosis
Up to 1 billion sperm cells produced / day
SOURCES OF GENETIC
VARIATION
•
1. Crossing Over
•
2. Independent Assortment
CROSSING OVER
•
In prophase 1, non-sister chromatids
can exchange pieces of
chromosomes
•
As a result, individual chromosomes
can contain genes of maternal origin
and some genes of paternal origin
•
Increases genetic diversity of the
gametes produced
INDEPENDENT
ASSORTMENT
•
In metaphase 1, homologous chromosomes line up in
the middle of the cell
•
Depending how the homologous chromosomes line up,
a number of different combinations of chromosomes
may be found in the gametes
HOMEWORK
•
Read pages 173-175
•
Pg. 181 # 1, 4, 6, 9, 11