Chapter 3.2
What is meiosis?
Sex cells

Sperm cells are male reproductive cell.

Eggs are female reproductive cell.
What is gamete?

Gamete- is a reproductive or sex cell. It
can mean either a sperm cell or an egg
cell.

Reproduction means making a baby.
Inheritance of chromosomes:
23 chromosomes in
a sperm cell
23 chromosomes in
an egg cell
46 chromosomes in a baby
Diploid vs. Haploid
Haploid- means a cell that contains only a
single set of chromosomes (23
chromosomes) and therefore only a single
set of genes. It’s only possible in sex cells
(sperm and
egg cells).
Diploid vs. Haploid
Diploid- means a cell that contains both
sets of homologous chromosomes
meaning: 23+23= 46 chromosomes (in
any cell: cheek cells, brain cells, heart
cells except for sex cells).
Body cells vs. gametes
Organism
Body cells
Fruit fly
8 (diploid
number of
chromosomes)
Gametes
(sperm or eggs)
4 (haploid
number of
chromosomes)
Bull frog
26
13
Human
46
23
MEIOSIS
Gametes (sperm or eggs) are produced
during a special process called MEIOSIS.
 It’s division of one cell (46 chromosomes)
into four cells (23 chromosomes).
 The number of chromosomes is cut in
half. Each gamete has only a half of
number of chromosomes.
 MEIOSIS-produces 4 genetically different
haploid sex cells.

MEIOSIS
Meiosis—the process happens in two
parts- meiosis I and meiosis II.
 It has a cross-over that results in
exchanging DNA between two
chromosomes.

Cross-over in meiosis
Mitosis vs. Meiosis
Mitosis results in the production of two
genetically identical diploid cells,
whereas meiosis produces four
genetically different haploid sex cells.
Checking concepts:
1. Describe the main results of meiosis.
How many human chromosomes does a
human egg cell have? Explain.
What would happen if the chromosomes
did not move to the opposite sides of
the nucleus before the cell pinched
apart?
Why is it important for gametes to have
half number of chromosomes?
What are the principal differences
between mitosis and meiosis?
What do the terms diploid and haploid
means?
Critical Thinking: In human cells, 2N = 46. How
many chromosomes would you expect to find in a
sperm cell? In an egg? In a white blood cell?
Explain.
A frog has 26 chromosomes in cells.
What is the number of chromosomes in
the frog’s gametes?
Fill in blanks:
1.
2.
3.
4.
All human body cells contain ______
chromosomes.
Sperm cells and egg cells are
________________________.
The process that reduces the number of
chromosomes in a cell by one-half is
_____________.
Meiosis occur only in the formation of
_____________.