Download Steps of Meiosis

Meiosis
The Production of Sex Cells
How many chromosomes does
a human body cell have?
46
How many chromosomes does
a human sex cell have?
23
each
The sex cell of females is
called?
• Egg
The sex cell of males is called?
• Sperm
• Cell size:
http://learn.genetics.utah.edu/content/begi
n/cells/scale
Why is it important that sex cells
have half the usual number of
chromosomes?
• So that the fertilized egg receives a normal
number of chromosomes
During what process are sex
cells made?
• Meiosis
– Produces sex cells with half the number of
chromosomes.
7)How
many
steps?
1
(Not counting
cytokinesis)
9
Prophase 2
8) How many chromosomes are
in a human cell at the start of
meiosis?
• 46
9) How many times
do the chromosomes
make copies of
themselves during
meiosis?
• once
1
Prophase 2
10) How many chromosomes
are in the human cell after
interphase?
• 92
1
11) How many divisions
does meiosis have?
2
Prophase 2
1
12) How many cells do
you start with in meiosis?
1
How many cells do you
end with?
4
Prophase 2
13) How many
chromosomes are
present in each
human cell at the
end of meiosis?
1
Prophase 2
23
14) Is each cell
produced at the end
of meiosis the
same?
Why?
1
Prophase 2
No
To allow for
genetic
variations
Steps of Meiosis
1. Interphase
- each chromosome
copies itself
Steps of Meiosis
2. Prophase I
- Homologous
chromosomes
(chromosomes that are the
same) line up together
Steps of Meiosis
3. Metaphase I
- Homologous
chromosomes line
up in the middle
and the spindle
attaches to the
centromere
Steps of Meiosis
4. Anaphase I
- The homologous
chromosomes move
to opposite ends of
the cell
- The centromere
does NOT split
Steps of Meiosis
5. Telophase I
- Cytokinesis occurs
making 2 new cells
- Each cell now has a
copy of each homologous
chromosome
Steps of Meiosis
• Between Telophase 1 and Prophase 2:
The cell now rests, no duplication of
chromosomes occurs
Steps of Meiosis
6. Prophase II
Steps of Meiosis
7) Metaphase II
Steps of Meiosis
8. Anaphase II
The centromere splits and sister chromatids
separate
Steps of Meiosis
9. Telophase II
Result
- 4 new daughter cells that are all genetically
different
- each new cell has half the number of
chromosomes as the original cell
Spermatogenesis
• Males produce 4 sperm each round of meiosis
Oogenesis
• Females produce 1 egg (ovum) and 3 polar
bodies each round of meiosis
Fertilization
• Fertilization will
restore the original
# of chromosomes
• 23 from egg
+ 23 from sperm
46 total
chromosomes to
make a human