Meiosis
Gametes are ____, meaning that they carry one of
each type of chromosome, while zygotes formed
by fertilization are ______ containing two of each
type of chromosome.
94%
1.
2.
3.
4.
Haploid, diploid
Monoploid, biploid
Monosomic,
disomic
Asexual, sexual
0%
1
2
6%
3
0%
4
If an organism contains 20 chromosomes in each
body (somatic) cell, then its gametes each contain
__ chromosomes.
10
20
5
15
1.
2.
3.
4.
61%
28%
6%
1
2
3
6%
4
Which figure shows mitosis?
72%
17%
1.
2.
3.
4.
The figure on the left
The figure on the right
Neither
both
11%
0%
1
2
3
4
_________ is used to produce new cells for growth and repair
or for generation of clones of an organism during asexual
reproduction. _______ is used to generate gametes for use
88%
in sexual reproduction.
1.
2.
Meiosis, mitosis
Mitosis, meiosis
12%
1
2
II. What is meiosis?
Meiosis is a process in which the number of
chromosomes per cell is cut in half through the
separation of homologous chromosomes in a
diploid (2n) cell.
 This will form 4 genetically different sex cells
(gametes) that are haploid (n).
 This means that it increases the differences
between people’s DNA so that every person is
genetically different.

II. What is meiosis?
23
23
23
III. Why does meiosis
happen?
Meiosis happens so that sperm and egg cells
can be produced so that sexual reproduction
can occur.
 Sexual reproduction is when two organisms
combine their genetic information to produce
genetically different offspring (babies).

Karyotype

Picture that shows all the chromosomes in a body
cell= of an organism = 23 pairs of homologous
chromosomes
used to diagnose
chromosomal disorders

(ex: Trisomy 21-Down Syndrome)
VI. What Happens During
Meiosis?
Before meiosis, our sex cells go through
interphase, where the DNA replicates and
the cell grows.
 DNA replication only occurs once in meiosis,
but there are two divisions!!! (Meiosis I and
Meiosis II)

VI. What happens during
meiosis?
Meiosis I:

There are four parts of Meiosis I;

Prophase I, Metaphase I, Anaphase I and
Telophase I.
VI. What happens during
meiosis?
VI. What happens during
meiosis?


The most important part of Meiosis I is Prophase I. During
Prophase crossing over occurs.
Crossing over is when parts of a chromosome exchange
with another chromosome. This occurs within each
homologous pair of chromosomes. This is important
because it increases genetic variation.
Independent Assortment

Independent Assortment occurs during metaphase I.


Creates genetic variation between gametes
Homologous pairs of chromosomes line up in the middle of
the cell in a random order each time.
VI. What happens during
meiosis?
Meiosis II:
 There are four parts of Meiosis II;
 Prophase II, Metaphase II, Anaphase II
and Telophase II.
VI. What happens during
meiosis?



At the end of Meiosis II, cytokinesis occurs.
Meiosis II resembles Mitosis.
The end result of the entire process of Meiosis (all 8 steps)
is four haploid cells that are genetically different. .
Mitosis vs. Meiosis

Mitosis





1 division
daughter cells
genetically identical to
parent cell
produces 2 cells
2n  2n
produces cells for
growth & repair

Meiosis





2 divisions
daughter cells
genetically different from
parent
produces 4 cells
2n  1n
produces gametes
Non-disjunctionchromosomes do not separate
properly during meiosis
Trisomy 21 : Down
Syndrome
Delayed mental and social skills
 Decreased muscle tone at birth
 Asymmetrical or odd-shaped skull
 Small skull
 Small mouth with protruding tongue
 Broad short hands
 Increased risk of developing
Leukemia and Alzheimer’s later in life

Trisomy 18 : Edward’s
Syndrome










Most children die in the first year of life, some have lived 10 years
Growth deficiency
Feeding difficulties
Breathing difficulties
Developmental delays
Mental Retardation
Overlapped, flexed fingers
Webbing of the second and third toes
Clubfeet
Structural heart defects at birth

Mitosis vs. Meiosis
Mitosis vs. Meiosis

Mitosis





1 division
daughter cells
genetically identical to
parent cell
produces 2 cells
2n  2n
produces cells for
growth & repair

Meiosis





2 divisions
daughter cells
genetically different from
parent
produces 4 cells
2n  1n
produces gametes
Cell A has 4 chromosomes and Cell D has 2
chromosomes. What process created Cell D?
1.
2.
3.
4.
Mitosis
Asexual
Reproduction
Fusion
Meiosis
Cell
A
Cell
B
Cell
C
Cell
D
10
Cell A is considered _______ while Cell D is
considered ________.
Haploid; Diploid
Tetrad; Diploid
Diploid; Haploid
Homologous; Haploid
1.
2.
3.
4.
Cell
A
0%
1
0%
0%
2
3
Cell
B
Cell
C
Cell
D
0%
4
10
Which of the numbers below best represents a
chromatid?
3
1
4
2
1.
2.
3.
4.
1
2
3
4
Cell
A
Cell B
0%
1
0%
2
0%
3
0%
4
10
Which of the numbers below best represents
homologous chromosomes?
3
1
4
2
1.
2.
3.
4.
1
2
3
4
Cell
A
Cell B
0%
1
0%
2
0%
3
10
0%
4
How can we best describe the diagram
below?
1.
2.
3.
4.
Two sister chromatids
Homologous chromosomes
One replicated chromosome
Haploid chromsomes
0%
1
0%
2
0%
3
0%
4
10
What process is best demonstrated by the diagram
below?
1.
2.
3.
4.
Anaphase I
Segregation of alleles
Crossing over
Independent assortment
0%
1
0%
2
0%
3
0%
4
10
Which of the following leads to genetic
variation during meiosis?
A. Crossing Over
B. DNA replication
C. Independent assortment
D. Mitotic spindle formation
1.
2.
3.
4.
5.
All of the above (A, B, C, D)
A&B
A&D
A, B, & D
A&C
0%
1
0%
0%
2
3
0%
0%
4
5
10
Which of the chromosomes below are
homologous to chromosome number one?
0%
0%
1.
2.
0%
0%
0%
0%
3.
4.
5.
6.
A
A and B
B and C
B
C
B and D
Blonde hair
Brown hair
A
B
C
Blue Eyes
D
ONE
10
Model Meiosis with Pop
Beads!!
Diploid =
4 chromosomes
(2 homolgous pairs)
Haploid =
2 chromosomes
Gametes should be
genetically different
due to crossing over
and independent
assortment.