1. Meiosis & Sexual Reproduction
Valentine’s Day
Perfect time to introduce the next subject in class

2. Biology, 9th ed,Sylvia Mader
Chapter 09
Asexual Reproduction
The prokaryotic chromosome is a ring of DNA
Binary fission
Splitting in two
Two replicate chromosomes are distributed to two daughter cells
Produces two daughter cells identical to original cell – asexual reproduction
The Cell Cycle

3. Binary Fission The Cell Cycle Biology, 9th ed,Sylvia Mader Chapter 09
Slide #3
Binary Fission
The Cell Cycle
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chromosome
1. Attachment of chromosome to
a special plasma membrane
site indicates that this
bacterium is about to divide.
cell wall
plasma
membrane
cytoplasm
2. The cell is preparing for binary
fission by enlarging its cell wall,
plasma membrane, and overall
volume.
3. DNA replication has produced
two identical chromosomes.
Cell wall and plasma membrane begin to grow inward.
4. As the cell elongates, the
chromosomes are pulled apart.
Cytoplasm is being distributed
evenly.
5. New cell wall and plasma
membrane has divided the
daughter cells.
© Dennis Kunkel Microscopy, Inc./Visuals Unlimited
SEM
2,345X

4. Sexual Reproduction Two parents Genetic variation Haploid gametes
Unique offspring
Similar to parents
Similar to each other

5. Haploid vs. Diploid HAPLOID 1n One copy of each chromosome DIPLOID 2n
Two copies of each chromosome
Homologous chromosomes

6. Homologous Chromosomes
Biology, 9th ed,Sylvia Mader
Chapter 10
Homologous Chromosomes
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a.
Sister chromatids
nonsister
chromatids
duplication
duplication
kinetochore
centromere
chromosome
homologous pair
chromosome
paternal chromosome
maternal chromosome b.
a: © L. Willatt/Photo Researchers, Inc.
Meiosis & Sexual Reproduction

7. Biology, 9th ed,Sylvia Mader
Overview of Meiosis
Chapter 10
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Diploid parent cell divides twice to make haploid gametes
Homologous chromosomes
Sister chromatids
2n = 4
Meiosis & Sexual Reproduction

8. Meiosis & Sexual Reproduction synapse and then separate.
Biology, 9th ed,Sylvia Mader
Overview of Meiosis
Chapter 10
Slide #8
Meiosis & Sexual Reproduction
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
centrioles
nucleolus
centromere
chromosome
duplication
2n = 4
2n = 4
MEIOSISI
Homologous pairs
synapse and then separate. 8

9. Overview of Meiosis Meiosis & Sexual Reproduction 9
Biology, 9th ed,Sylvia Mader
Overview of Meiosis
Chapter 10
Slide #9
Meiosis & Sexual Reproduction
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
First division
Second division
Four haploid
daughter cells
centrioles
nucleolus
sister chromatids
centromere
synapsis
chromosome
duplication
2n = 4
2n = 4
n = 2
n = 2
MEIOSISI
Homologous pairs
synapse and then separate.
MEIOSISII
Sister chromatids separate,
becoming daughter chromosomes. 9

10. Genetic Variation For humans - 23 pairs of chromosomes:
Independent Assortment – 50/50 chance that gamete gets maternal/ paternal homologous chromosome
# of possible gametes = 223
>8 million possible gamete combinations
Random Fertilization
(8 million)(8 million) = 64 trillion possible offspring
Crossing over – increases genetic variation even more

11. Independent Assortment
Biology, 9th ed,Sylvia Mader
Chapter 10
Independent Assortment
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Combination 7
Combination 3
Combination 5
Combination 1
Combination 2
Combination 4
Combination 6
Combination 8
Meiosis & Sexual Reproduction

12. Crossing Over Occurs During Meiosis I
Biology, 9th ed,Sylvia Mader
Chapter 10
Crossing Over Occurs During Meiosis I
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
nucleoprotein lattice
sister chromatids
of a chromosome
sister chromatids
of its homologue A A a a A a B B b b B b
chiasmata of
nonsister
chromatids
1 and 3 c C C c C c D D d d D d 1 2 3 4 1 2 3 4 1 2 3 4
Bivalent
forms
Crossing-over
has occurred
Daughter
chromosomes a. b. c. d.
a: Courtesy Dr. D. Von Wettstein
Meiosis & Sexual Reproduction

13. Crossing Over Increases genetic variation Synapsis Tetrad Chiasma
Happens during Prophase I

14. Biology, 9th ed,Sylvia Mader
Chapter 10
Genetic Variation
Significance of genetic variation:
Asexual reproduction produces genetically identical clones
Sexual reproduction causes genetic recombinations among members of a population
Asexual reproduction is advantageous when the environment is stable
However, if the environment changes, genetic variability introduced by sexual reproduction may be advantageous
Some offspring may have a better chance of survival
Meiosis & Sexual Reproduction

15. Karyotyping

16. Mitosis vs. Meiosis

17. Meiosis Compared to Mitosis
Biology, 9th ed,Sylvia Mader
Chapter 10
Meiosis Compared to Mitosis
Meiosis
2 nuclear divisions
Chromosomes cross over
Halves chromosome number
Produces 4 genetically different daughter cells
Used only for sexual reproduction
Mitosis
1 nuclear division
Chromosomes don’t cross over
Preserves chromosome number
Produces 2 genetically identical daughter cells
Used for asexual reproduction & growth
Meiosis & Sexual Reproduction

18. Life Cycles

19. Meiosis & Sexual Reproduction
Biology, 9th ed,Sylvia Mader
Life Cycle of Humans
Chapter 10
Slide #19
Meiosis & Sexual Reproduction
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
MITOSIS 2n 2n 2n
MITOSIS 2n
zygote
2n = 46
diploid (2n)
FERTILIZATION
MEIOSIS
haploid (n)
n = 23 n n
egg
sperm 19

20. Biology, 9th ed,Sylvia Mader
Spermatogenesis and Oogenesis in Mammals
Chapter 10
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
SPERMATOGENESIS
OOGENESIS
primary
spermatocyte
primary
oocyte 2 n 2n
Meiosis I
Meiosis I
first
polarbody
secondary
spermatocytes n
secondary
oocyte n
Meiosis II n
Meiosis II
spermatids
Meiosis II is completed
after entry of sperm (fertilization) n
second
polarbody n
Metamorphosis
and maturation
Fertilization
egg n
sperm
Sperm nucleus n n
fusion of sperm
nucleus and
agg nucleus
zygote 2n
Meiosis & Sexual Reproduction

21. Changes in Chromosome Number & Structure
Euploidy: correct number of chromosomes
Aneuploidy: change in the chromosome number
Results from nondisjunction
Monosomy - 1
Trisomy - 3

22. Nondisjunction 22 pair of homologous chromosomes pair of homologous
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pair of
homologous
chromosomes
pair of
homologous
chromosomes
nondisjunction
Meiosis I
normal
Meiosis II
normal
nondisjunction
nondisjunction 22

23. Nondisjunction 23 pair of homologous chromosomes pair of homologous
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pair of
homologous
chromosomes
pair of
homologous
chromosomes
nondisjunction
Meiosis I
normal
Meiosis II
normal
nondisjunction
Fertilization
Zygote
2n + 1
2n + 1
2n - 1
2n - 1 2n 2n
2n + 1
2n - 1 a. b. 23

24. a: © Jose Carrilo/PhotoEdit; b: © CNRI/SPL/Photo Researchers
Trisomy 21
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extra chromosome 21 a. b.
a: © Jose Carrilo/PhotoEdit; b: © CNRI/SPL/Photo Researchers

25. Changes in Sex Chromosome
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a. Turner syndrome
missing
chromosome X
b. Klinefelter syndrome
extra
chromosome X
a(top): Courtesy UNC Medical Illustration and Photograph; b(top): Courtesy Stefan D. Schwarz, a, b(bottom): © CNRI/SPL/Photo Researchers, Inc

26. Types of Chromosomal Mutation
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a a a b b b b c c c c + a d d d d e e e e f d f f e g g g f g
a. Deletion
b. Duplication a a a a b b l b b l c m c c m d d n d n d c e o e o e e f p f p f f g q q g g g h r r h
c. Inversion d.
Translocation