 Meiosis is the type of nuclear division that
reduces the chromosome number from the
diploid (2n) number to the haploid (n)
number.
 In humans, the diploid number of 46 is
reduced to the haploid number of 23.
2
 Gametes (reproductive cells, often the sperm
and egg) have the haploid number of
chromosomes (1n).
 Fusion of gametes form a cell called a zygote.
A zygote always has the full or diploid (2n)
number of chromosomes. In plants and
animals, the zygote undergoes development
to become an adult organism.
3
In diploid body cells, the chromosomes occur in
pairs which are called Homologous
chromosomes or homologues.
4
Exchange of genetic material between non-sister
chromatids of a bivalent during meiosis. (This occurs
during Meiosis 1 / Prophase 1).
5
Meiosis requires two nuclear divisions and
produces four haploid daughter cells, each having
half the total number of chromosome.
• Production of haploid gametes to maintain
the diploid number of species, generation
after generation.
• Crossing-over, which brings together new
gene combination of chromosomes and that
lead to genetic variations.
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MEIOSIS CONSISTS OF TWO UNIQUE CELL DIVISIONS
Meiosis I
Prophase I
Metaphase
I
Anaphase I
Telophase I
Meiosis II
Prophase II
Metaphase
II
Anaphase
II
Telophase
II
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9
10
11
12
In human males, spermatogenesis occurs
within the testes, and in females,
oogenesis occurs within the ovaries.
Secondary
The
testes
of
Primary spermatocytes
human male undergo
spermatocytes
with
46 chromosomes
contain
stem cells
meiosis II to produce
called
undergo meiosis I to
spermatogonia,
and
four
spermatids with
23
form
two
secondary
these
cells
keep the
daughter chromosomes.
testes suppliedeach
spermatocytes,
Spermatids
with
primary then
with
23 duplicated
spermatocytes
that
differentiate into viable
undergo
chromosomes.
sperm
(spermatozoa).
spermatogenesis.
14
Theother
ovaries
contain
The
is
a polar
body
The
result
of
meiosis
I
They even begin
stem
cells
called
that
may
either
is two haploid cells
oogenesis, but only a
oogonia thator
produce
disintegrate
divide
with
23 chromosomes,
few continue
when a
many primary
again.
The secondary
One
of these
cells,
female
is
sexually
oocytes with 46
oocyte begins meiosis II
termed
the
secondary
mature.
chromosomes
during
but stops at metaphase
oocyte
receives
fetal
development.
II.
Then
the
secondary
almostleaves
all thethe ovary
oocyte
and
enters an oviduct.
cytoplasm.
15
Video link for mitosis on
 http://www.youtube.com/watch?v=65SODTL_QsA
(Right Click then choose open Hyperlink)
Download the video (student must watch most of it)
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‫‪17‬‬
‫البالغ (يقصد بها النضوج الجنسي)‬
‫‪adult‬‬
‫تبادل‬
‫‪Exchange‬‬
‫عملية انتاج الحيوانات المنوية‬
‫‪Spermatogenesis‬‬
‫عملية انتاج البويضات‬
‫‪Oogenesis‬‬
‫الخصيتان‬
‫‪testes‬‬
‫المبيض‬
‫‪ovaries‬‬
Test Your Self
‫إختبر نفسك‬
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1- Sexual reproduction _____.
A) requires haploid gametes
B) results in a diploid zygote
C) creates offspring that are genetically different from the parents
D) All of these
2- Once duplicated, a chromosome is composed of two identical parts
called _____.
A) sister chromatids
B) centromeres
C) homologous chromosomes
D) chiasmata
3- Sexual reproduction contributes greatly to the process of _____.
A) evolution
B) metabolism
C) organization
D) growth and repair
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4- The combining of chromosomes from genetically different gametes
occurs during _____.
A) crossing over
B) synapsis
C) meiosis II
D) fertilization
5- In animals the haploid cells produced by meiosis mature and become
_____.
A) spores
B) zygotes
C) gametes
D) diploid
6- A primary spermatocyte with 46 chromosomes will undergo meiosis and
yield _____.
A) four spermatids with 46 chromosomes
B) four spermatids with 23 chromosomes
C) two spermatids with 46 chromosomes
D) two spermatids with 23 chromosomes
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7- In females, meiosis is a part of _____, which occurs in the ovaries and
produces eggs.
A) fertilization
B) oogenesis
C) the alternation of generations
D) spermatogenesis
8- When a primary spermatocyte undergoes meiosis I, two _____ secondary
spermatocytes are produced.
A) diploid
B) haploid
C) triploidy
9- Mitosis occurs in humans during _____.
A) development of the zygote
B) growth of a child
C) repair of tissue at any time
D) All of these
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10 - Which phase is characterized by the haploid number of duplicated
chromosomes at the metaphase plate?
A) meiosis II metaphase II
B) mitosis prophase
C) meiosis II telophase II
D) meiosis I metaphase I
11- Which of the following results in diploid daughter cells?
A) meiosis I
B) meiosis II
C) mitosis
12- Which is true of both meiosis II and mitosis?
A) Pairing of chromosomes
B) Diploid number of chromosomes at the metaphase plate
C) Separation of sister chromatids
D) Four daughter cells
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13- Which is characteristic of meiosis I?
A) Pairing of chromosomes
B) Separation of sister chromatids
C) Diploid daughter cells
D) All of these
14- At the end of telophase II and cytokinesis there are __________ haploid
cells.
A) two
B) four
C) six
15- The homologues of each bivalent separate and move to opposite poles
during _____.
A) prophase I
B) metaphase II
C) anaphase I
D) anaphase II
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16- Crossing over between nonsister chromatids occurs during _____.
A) interkinesis
B) prophase I
C) telophase I
D) anaphase II
17- Turner's syndrome is _______.
A) produced by mutation
B) produced by nondisjunction of an autosome
C) produced by nondisjunction of an X chromosome
D) trisomy X
18- Down Syndrome is an example of _______.
A) polyploidism
B) trisomy
C) monosomy
D) abnormality in embryonic development
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19- At the completion of meiosis II, there are _____ daughter cells.
A) two haploid
B) two diploid
C) four haploid
D) four diploid
20- The diploid number of chromosomes is restored after _____ so that
an animal's body cells contain the diploid number of chromosomes.
A) meiosis I
B) meiosis II
C) fertilization
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Thank You
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