1. Chapter IV Part 2 Reproduction of EUKARYOTIC cellBy
Pn. Aslizah Binti Mohd Aris

2. Overview: Variations on a Theme
Living organisms are distinguished by their ability to reproduce their own kind
Genetics is the scientific study of heredity and variation
Heredity is the transmission of traits from one generation to the next
Variation is demonstrated by the differences in appearance that offspring show from parents and siblings
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3. Figure 13.1 What accounts for family resemblance?

4. Comparison of Asexual and Sexual Reproduction
In asexual reproduction, one parent produces genetically identical offspring by mitosis
A clone is a group of genetically identical individuals from the same parent
In sexual reproduction, two parents give rise to offspring that have unique combinations of genes inherited from the two parents
Video: Hydra Budding
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5. 0.5 mm Parent Bud (a) Hydra (b) Redwoods
Fig. 13-2
0.5 mm
Parent
Bud
Figure 13.2 Asexual reproduction in two multicellular organisms
(a) Hydra
(b) Redwoods

6. Sets of Chromosomes in Human Cells
Human somatic cells (any cell other than a gamete) have 23 pairs of chromosomes
A karyotype is an ordered display of the pairs of chromosomes from a cell
The two chromosomes in each pair are called homologous chromosomes, or homologs
Chromosomes in a homologous pair are the same length and carry genes controlling the same inherited characters
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7. Figure 13.3 Preparing a karyotype
APPLICATION
TECHNIQUE
5 µm
Pair of homologous
replicated chromosomes
Centromere
Figure 13.3 Preparing a karyotype
Sister
chromatids
Metaphase
chromosome

8. The sex chromosomes are called X and Y
Human females have a homologous pair of X chromosomes (XX)
Human males have one X and one Y chromosome
The 22 pairs of chromosomes that do not determine sex are called autosomes
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9. A diploid cell (2n) has two sets of chromosomes
Each pair of homologous chromosomes includes one chromosome from each parent
The 46 chromosomes in a human somatic cell are two sets of 23: one from the mother and one from the father
A diploid cell (2n) has two sets of chromosomes
For humans, the diploid number is 46 (2n = 46)
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10. Key Maternal set of chromosomes (n = 3) 2n = 6 Paternal set of
Fig. 13-4
Key
Maternal set of
chromosomes (n = 3)
2n = 6
Paternal set of
chromosomes (n = 3)
Two sister chromatids
of one replicated
chromosome
Centromere
Figure 13.4 Describing chromosomes
Two nonsister
chromatids in
a homologous pair
Pair of homologous
chromosomes
(one from each set)

11. For humans, the haploid number is 23 (n = 23)
A gamete (sperm or egg) contains a single set of chromosomes, and is haploid (n)
For humans, the haploid number is 23 (n = 23)
Each set of 23 consists of 22 autosomes and a single sex chromosome
In an unfertilized egg (ovum), the sex chromosome is X
In a sperm cell, the sex chromosome may be either X or Y
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12. Behavior of Chromosome Sets in the Human Life Cycle
Fertilization is the union of gametes (the sperm and the egg)
The fertilized egg is called a zygote and has one set of chromosomes from each parent
The zygote produces somatic cells by mitosis and develops into an adult
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13. At sexual maturity, the ovaries and testes produce haploid gametes
Gametes are the only types of human cells produced by meiosis, rather than mitosis
Meiosis results in one set of chromosomes in each gamete
Fertilization and meiosis alternate in sexual life cycles to maintain chromosome number
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14. Multicellular diploid adults (2n = 46)
Fig. 13-5
Key
Haploid gametes (n = 23)
Haploid (n)
Egg (n)
Diploid (2n)
Sperm (n)
MEIOSIS
FERTILIZATION
Ovary
Testis
Diploid
zygote
(2n = 46)
Figure 13.5 The human life cycle
Mitosis and
development
Multicellular diploid
adults (2n = 46)

15. The Variety of Sexual Life Cycles
The alternation of meiosis and fertilization is common to all organisms that reproduce sexually
The three main types of sexual life cycles differ in the timing of meiosis and fertilization
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16. Gametes are the only haploid cells in animals
In animals, meiosis produces gametes, which undergo no further cell division before fertilization
Gametes are the only haploid cells in animals
Gametes fuse to form a diploid zygote that divides by mitosis to develop into a multicellular organism
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17. Figure 13.6 Three types of sexual life cycles
Key
Haploid (n)
Haploid unicellular or
multicellular organism
Diploid (2n)
Haploid multi-
cellular organism
(gametophyte) n
Gametes n n
Mitosis n
Mitosis
Mitosis n
Mitosis n n n n n
MEIOSIS
FERTILIZATION
Spores n
Gametes n
Gametes n
MEIOSIS
FERTILIZATION
Zygote
MEIOSIS
FERTILIZATION 2n 2n 2n 2n
Diploid
multicellular
organism
Zygote
Diploid
multicellular
organism
(sporophyte) 2n
Mitosis
Mitosis
Zygote
Figure 13.6 Three types of sexual life cycles
(a) Animals
(b) Plants and some algae
(c) Most fungi and some protists

18. Meiosis reduces the number of chromosome sets from diploid to haploid
Like mitosis, meiosis is preceded by the replication of chromosomes
Meiosis takes place in two sets of cell divisions, called meiosis I and meiosis II
The two cell divisions result in four daughter cells, rather than the two daughter cells in mitosis
Each daughter cell has only half as many chromosomes as the parent cell
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19. The Stages of Meiosis
In the first cell division (meiosis I), homologous chromosomes separate
Meiosis I results in two haploid daughter cells with replicated chromosomes; it is called the reductional division
In the second cell division (meiosis II), sister chromatids separate
Meiosis II results in four haploid daughter cells with unreplicated chromosomes; it is called the equational division
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20. Figure 13.7 Overview of meiosis: how meiosis reduces chromosome number
Interphase
Homologous pair of chromosomes
in diploid parent cell
Chromosomes
replicate
Homologous pair of replicated chromosomes
Sister
chromatids
Diploid cell with
replicated
chromosomes
Meiosis I 1
Homologous
chromosomes
separate
Figure 13.7 Overview of meiosis: how meiosis reduces chromosome number
Haploid cells with
replicated chromosomes
Meiosis II 2
Sister chromatids
separate
Haploid cells with unreplicated chromosomes

21. Meiosis I
Meiosis I is preceded by interphase, in which chromosomes are replicated to form sister chromatids
The sister chromatids are genetically identical and joined at the centromere
The single centrosome replicates, forming two centrosomes
For the Cell Biology Video Meiosis I in Sperm Formation, go to Animation and Video Files.
BioFlix: Meiosis
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22. Figure 13.8 The meiotic division of an animal cell
Prophase I
Metaphase I
Anaphase I
Telophase I and
Cytokinesis
Prophase II
Metaphase II
Anaphase II
Telophase II and
Cytokinesis
Centrosome
(with centriole pair)
Sister chromatids
remain attached
Centromere
(with kinetochore)
Sister
chromatids
Chiasmata
Spindle
Metaphase
plate
Sister chromatids
separate
Haploid daughter cells
forming
Homologous
chromosomes
Homologous
chromosomes
separate
Cleavage
furrow
Fragments
of nuclear
envelope
Microtubule
attached to
kinetochore
Figure 13.8 The meiotic division of an animal cell

23. Division in meiosis I occurs in four phases:
– Prophase I
– Metaphase I
– Anaphase I
– Telophase I and cytokinesis
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24. Prophase I Metaphase I Anaphase I Centrosome (with centriole pair)
Fig. 13-8a
Telophase I and
Cytokinesis
Prophase I
Metaphase I
Anaphase I
Centrosome
(with centriole pair)
Sister chromatids
remain attached
Centromere
(with kinetochore)
Sister
chromatids
Chiasmata
Spindle
Metaphase
plate
Cleavage
furrow
Homologous
chromosomes
Homologous
chromosomes
separate
Figure 13.8 The meiotic division of an animal cell
Fragments
of nuclear
envelope
Microtubule
attached to
kinetochore

25. Prophase I
Prophase I typically occupies more than 90% of the time required for meiosis
Chromosomes begin to condense
In synapsis, homologous chromosomes loosely pair up, aligned gene by gene
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26. In crossing over, nonsister chromatids exchange DNA segments
Each pair of chromosomes forms a tetrad, a group of four chromatids
Each tetrad usually has one or more chiasmata, X-shaped regions where crossing over occurred
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27. Metaphase I
In metaphase I, tetrads line up at the metaphase plate, with one chromosome facing each pole
Microtubules from one pole are attached to the kinetochore of one chromosome of each tetrad
Microtubules from the other pole are attached to the kinetochore of the other chromosome
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28. Prophase I Metaphase I Centrosome (with centriole pair) Centromere
Fig. 13-8b
Prophase I
Metaphase I
Centrosome
(with centriole pair)
Centromere
(with kinetochore)
Sister
chromatids
Chiasmata
Spindle
Metaphase
plate
Figure 13.8 The meiotic division of an animal cell
Homologous
chromosomes
Fragments
of nuclear
envelope
Microtubule
attached to
kinetochore

29. Anaphase I In anaphase I, pairs of homologous chromosomes separate
One chromosome moves toward each pole, guided by the spindle apparatus
Sister chromatids remain attached at the centromere and move as one unit toward the pole
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30. Telophase I and Cytokinesis
In the beginning of telophase I, each half of the cell has a haploid set of chromosomes; each chromosome still consists of two sister chromatids
Cytokinesis usually occurs simultaneously, forming two haploid daughter cells
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31. In animal cells, a cleavage furrow forms; in plant cells, a cell plate forms
No chromosome replication occurs between the end of meiosis I and the beginning of meiosis II because the chromosomes are already replicated
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32. Telophase I and Cytokinesis
Fig. 13-8c
Telophase I and
Cytokinesis
Anaphase I
Sister chromatids
remain attached
Figure 13.8 The meiotic division of an animal cell
Homologous
chromosomes
separate
Cleavage
furrow

33. Meiosis II Division in meiosis II also occurs in four phases:
– Prophase II
– Metaphase II
– Anaphase II
– Telophase II and cytokinesis
Meiosis II is very similar to mitosis
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34. Telophase II and Cytokinesis
Fig. 13-8d
Telophase II and
Cytokinesis
Prophase II
Metaphase II
Anaphase II
Sister chromatids
separate
Haploid daughter cells
forming
Figure 13.8 The meiotic division of an animal cell

35. Prophase II In prophase II, a spindle apparatus forms
In late prophase II, chromosomes (each still composed of two chromatids) move toward the metaphase plate
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36. Metaphase II
In metaphase II, the sister chromatids are arranged at the metaphase plate
Because of crossing over in meiosis I, the two sister chromatids of each chromosome are no longer genetically identical
The kinetochores of sister chromatids attach to microtubules extending from opposite poles
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37. Prophase II Metaphase II
Fig. 13-8e
Prophase II
Metaphase II
Figure 13.8 The meiotic division of an animal cell

38. Anaphase II In anaphase II, the sister chromatids separate
The sister chromatids of each chromosome now move as two newly individual chromosomes toward opposite poles
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39. Telophase II and Cytokinesis
In telophase II, the chromosomes arrive at opposite poles
Nuclei form, and the chromosomes begin decondensing
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40. Cytokinesis separates the cytoplasm
At the end of meiosis, there are four daughter cells, each with a haploid set of unreplicated chromosomes
Each daughter cell is genetically distinct from the others and from the parent cell
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41. Telephase II and Cytokinesis
Fig. 13-8f
Telephase II and
Cytokinesis
Anaphase II
Sister chromatids
separate
Haploid daughter cells
forming
Figure 13.8 The meiotic division of an animal cell

42. A Comparison of Mitosis and Meiosis
Mitosis conserves the number of chromosome sets, producing cells that are genetically identical to the parent cell
Meiosis reduces the number of chromosomes sets from two (diploid) to one (haploid), producing cells that differ genetically from each other and from the parent cell
The mechanism for separating sister chromatids is virtually identical in meiosis II and mitosis
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43. Figure 13.9 A comparison of mitosis and meiosis in diploid cells
Chiasma
MEIOSIS I
Parent cell
Chromosome
replication
Chromosome
replication
Prophase
Prophase I
Homologous
chromosome
pair
Replicated chromosome
2n = 6
Metaphase
Metaphase I
Anaphase
Anaphase I
Telophase
Telophase I
Haploid
n = 3
Daughter
cells of
meiosis I 2n 2n
MEIOSIS II
Daughter cells
of mitosis n n n n
Daughter cells of meiosis II
SUMMARY
Figure 13.9 A comparison of mitosis and meiosis in diploid cells
Property
Mitosis
Meiosis
DNA
replication
Occurs during interphase before
mitosis begins
Occurs during interphase before meiosis I begins
Number of
divisions
One, including prophase, metaphase,
anahase, and telophase
Two, each including prophase, metaphase, anaphase, and
telophase
Synapsis of
homologous
chromosomes
Does not occur
Occurs during prophase I along with crossing over
between nonsister chromatids; resulting chiasmata
hold pairs together due to sister chromatid cohesion
Number of
daughter cells
and genetic
composition
Two, each diploid (2n) and genetically
identical to the parent cell
Four, each haploid (n), containing half as many chromosomes
as the parent cell; genetically different from the parent
cell and from each other
Role in the
animal body
Enables multicellular adult to arise from
zygote; produces cells for growth, repair,
and, in some species, asexual reproduction
Produces gametes; reduces number of chromosomes by half
and introduces genetic variability amoung the gametes

44. You should now be able to:
Distinguish between the following terms: somatic cell and gamete; autosome and sex chromosomes; haploid and diploid
Describe the events that characterize each phase of meiosis
Describe three events that occur during meiosis I but not mitosis
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45. Spermatogenesis is production of mature sperm
The timing and pattern of meiosis in mammals differ for males and females
Gametogenesis, the production of gametes by meiosis, differs in females and males
Sperm are small and motile and are produced throughout the life of a sexually mature male
Spermatogenesis is production of mature sperm

46. Spermatogenesis and oogenesis in an animal cell

47. Spermatogenesis
In diploid animals, the only haploid cells are gametes produced by meiosis and used in sexual reproduction. Gametes are produced by specialized cells.
In males, spermatogenesis produces spermatozoa within the testes.
Primordial germ cells (primary spermatogonia) undergo mitosis to produce secondary spermatogonia.
Secondary spermatogonia transform into primary spermatocytes (meiocytes), which undergo meiosis I, giving rise to two secondary spermatocytes.
Each secondary spermatocyte undergoes meiosis II, producing haploid spermatids that differentiate into spermatozoa.

48. Figure 46.12 Human gametogenesis
Fig a
Epididymis
Seminiferous tubule
Testis
Cross section of seminiferous tubule
Primordial germ cell in embryo
Mitotic divisions
Sertoli cell nucleus
Spermatogonial stem cell 2n
Mitotic divisions
Spermatogonium 2n
Mitotic divisions
Primary spermatocyte 2n
Meiosis I
Lumen of seminiferous tubule
Secondary spermatocyte n n
Figure Human gametogenesis
For the Cell Biology Video Motion of Isolated Flagellum, go to Animation and Video Files.
For the Cell Biology Video Flagellum Movement in Swimming Sperm, go to Animation and Video Files.
Meiosis II
Neck
Spermatids (at two stages of differentiation)
Early spermatid n n n n
Tail
Midpiece
Head
Plasma membrane
Differentiation (Sertoli cells provide nutrients)
Mitochondria
Sperm n n n n
Nucleus
Acrosome

49. Primordial germ cell in embryo
Fig c
Primordial germ cell in embryo
Mitotic divisions
Spermatogonial stem cell 2n
Mitotic divisions
Spermatogonium 2n
Mitotic divisions
Primary spermatocyte 2n
Meiosis I
Secondary spermatocyte n n
Meiosis II
Early spermatid n n n n
Figure Human gametogenesis
Differentiation (Sertoli cells provide nutrients)
Sperm n n n n

50. Oogenesis In females, oogenesis produces eggs (oocytes) in the ovary.
Primordial germ cells (primary oogonia) undergo mitosis to produce secondary oogonia.
Secondary oogonia transform into primary oocytes, which grow until the end of oogenesis.
Primary oocytes undergo meiosis I and unequal cytokinesis, producing a large secondary oocyte, and a small cell called the first polar body.
The secondary oocyte produces two haploid cells in meiosis II. One is a very small cell, the second polar body, and the other rapidly matures into an ovum.
(5) The first polar body may or may not divide during meiosis I. Polar bodies have no function in most species and degenerate, so that a round of meiosis produces only one viable gamete, the ovum. Human oocytes form in the fetus, completing meiosis only after fertilization.

51. Oogenesis Eggs contain stored nutrients and are much larger
Oogenesis is development of mature oocytes (eggs) and can take many years

52. Figure 46.12 Human gametogenesis
Fig e
Ovary
Primary oocyte within follicle
In embryo
Growing follicle
Primordial germ cell
Mitotic divisions 2n
Oogonium
Mitotic divisions
Primary oocyte (present at birth), arrested in prophase of meiosis I 2n
Mature follicle
Ruptured follicle
Completion of meiosis I and onset of meiosis II
First polar body n n
Secondary oocyte, arrested at metaphase of meiosis II
Figure Human gametogenesis
Ovulated secondary oocyte
Ovulation, sperm entry
Completion of meiosis II
Second polar body
Corpus luteum n n
Fertilized egg
Degenerating corpus luteum

53. Figure 46.12 Human gametogenesis
Fig g
In embryo
Primordial germ cell
Mitotic divisions 2n
Oogonium
Mitotic divisions
Primary oocyte (present at birth), arrested in prophase of meiosis I 2n
Completion of meiosis I and onset of meiosis II
First polar body n n
Secondary oocyte, arrested at metaphase of meiosis II
Ovulation, sperm entry
Figure Human gametogenesis
Completion of meiosis II
Second polar body n
Fertilized egg n

54. Spermatogenesis differs from oogenesis:
In oogenesis, one egg forms from each cycle of meiosis; in spermatogenesis four sperm form from each cycle of meiosis
Oogenesis ceases later in life in females; spermatogenesis continues throughout the adult life of males
Oogenesis has long interruptions; spermatogenesis produces sperm from precursor cells in a continuous sequence