1. Chapter 10 Meiosis and Sexual Reproduction
BIOLOGY
Mader
Chapter 10 Meiosis and Sexual Reproduction

2. Types of Reproduction Parent Bud 0.5 mm
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

3. Figure 13.4 Describing chromosomes
Key
Maternal set of
chromosomes (n = 3)
Paternal set of
2n = 6
Two sister chromatids
of one replicated
chromosome
Two nonsister
chromatids in
a homologous pair
Pair of homologous
chromosomes
(one from each set)
Centromere
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

4. Figure 13.5 The human life cycle At fertilization, a sperm fuses with an egg, forming a diploid zygote
Key
Haploid (n)
Diploid (2n)
Haploid gametes (n = 23)
Ovum (n)
Sperm
Cell (n)
MEIOSIS
FERTILIZATION
Ovary
Testis
Diploid
zygote
(2n = 46)
Mitosis and
development
Multicellular diploid
adults (2n = 46)
Repeated mitotic divisions lead to the development of a mature adult
The adult makes haploid gametes by meiosis
All of these processes make up the sexual life cycle of organisms
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

5. Chromosomes are matched in homologous pairs
MEIOSIS
Chromosomes are matched in homologous pairs
Somatic cells of each species contain a specific number of chromosomes
Human cells have 46, making up 23 pairs of homologous chromosomes
Chromosomes
Centromere
Sister chromatids
Figure 8.12
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

6. Gametes have a single set of chromosomes
Cells with two sets of chrom. are said to be diploid (2n = 46 for humans)
Gametes are haploid, with only one set of chromosomes (n = 23 for humans)
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

7. Homologous chromosomes carry different versions of genes
The differences between homologous chromosomes are based on the fact that they can carry different versions of a gene (called alleles) at corresponding loci (i.e. gene for eye color might say “blue” on dad, but “brown” on mom)
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

8. C E C E C E c e c e c e Coat-color genes Eye-color genes Brown Black
White
Pink
Tetrad in parent cell (homologous pair of duplicated chromosomes)
Chromosomes of the four gametes
Figure 8.17A, B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

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

10. Overview of 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 1 2
Homologous
separate
Haploid cells with
replicated chromosomes
Sister chromatids
Haploid cells with unreplicated chromosomes
Meiosis I
Meiosis II
Overview of meiosis: reduces chromosome number
Meiosis, like mitosis, is preceded by chromosome duplication (during interphase)
However, in meiosis the cell divides twice to form four daughter cells, each of which is haploid (n = 23).
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

11. Meiosis Men vs. Women Spermatogenesis: Oogenesis Men Testes
4 cells produced
145 rounds
6 days
Oogenesis
Women
Ovaries
Uneven separation results in 4 cells, one called egg
Born = 1-2 million oocytes (prophase I)
Puberty = 400,000

12. The Meiotic Division of an Animal Cell
Centrosomes
(with centriole pairs)
Sister
chromatids
Chiasmata
Spindle
Tetrad
Nuclear
envelope
Chromatin
Centromere
(with kinetochore)
Microtubule
attached to
kinetochore
Tetrads line up
Metaphase
plate
Homologous
chromosomes
separate
Sister chromatids
remain attached
Pairs of homologous
chromosomes split up
Chromosomes duplicate
Homologous chromosomes
(red and blue) pair and exchange
segments; 2n = 6 in this example
INTERPHASE
MEIOSIS I: Separates homologous chromosomes
PROPHASE I
METAPHASE I
ANAPHASE I
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

14. Meiosis II is essentially the same as mitosis
The sister chromatids of each chromosome separate
The result is four haploid daughter cells, each of which are haploid (n = 23).
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

15. Meiosis - 2 divisions....WHY?
In the first division, meiosis I, homologous chromosomes are paired. (While they are paired, they can cross over and exchange genetic information)
The homologous pairs are then separated, and two daughter cells are produced, which at this point are haploid (n = 23).
But because each chromosome has double the genetic info (2 sister chromatids), another division is necessary.
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

16. Figure 13.8 The Meiotic Division of an Animal Cell
TELOPHASE I AND
CYTOKINESIS
PROPHASE II
METAPHASE II
ANAPHASE II
TELOPHASE II AND
MEIOSIS II: Separates sister chromatids
Cleavage
furrow
Sister chromatids
separate
Haploid daughter cells
forming
During another round of cell division, the sister chromatids finally separate;
four haploid daughter cells result, containing single chromosomes
Two haploid cells
form; chromosomes
are still double
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

17. Genetic Variation: Independent Assortment
Biology, 9th ed,Sylvia Mader
Chapter 10
Genetic Variation: Independent Assortment
Independent assortment:
When homologues align at the metaphase plate:
They separate in a random manner
The maternal or paternal homologue may be oriented toward either pole of mother cell
Causes random mixing of blocks of alleles into gametes
Meiosis & Sexual Reproduction

18. The independent assortment of homologous chromosomes in meiosis
Key
Maternal set of
chromosomes
Paternal set of
Possibility 1
Two equally probable
arrangements of
chromosomes at
metaphase I
Possibility 2
Metaphase II
Daughter
cells
Combination 1
Combination 2
Combination 3
Combination 4
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

19. Independent Assortment
Biology, 9th ed,Sylvia Mader
Chapter 10
Independent Assortment
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Meiosis & Sexual Reproduction

20. What leads to variability/diversity?
Why are we not all identical?
Independent assortment
Crossing over
Random fertilization
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

21. Processes allowing for increased GENETIC DIVERSITY
Random Fertilization - Each chromosome of a homologous pair comes from a different parent. (Which sperm will fertilize the egg? Or Which 2 people will produce offspring together?)
Each chromosome thus differs at many points from the other member of the pair (different alleles)
Crossing over
Independent assortment
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

22. Genetic Variation: Significance
Biology, 9th ed,Sylvia Mader
Chapter 10
Genetic Variation: Significance
Asexual reproduction produces genetically identical clones
Sexual reproduction cause novel genetic recombinations
Asexual reproduction is advantageous when environment is stable
However, if environment changes, genetic variability introduced by sexual reproduction may be advantageous
Offspring adapt to that environment
Meiosis & Sexual Reproduction

23. Random Fertilization

24. Genetic Variation: Fertilization
Biology, 9th ed,Sylvia Mader
Chapter 10
Genetic Variation: Fertilization
When gametes fuse at fertilization:
Chromosomes donated by the parents are combined
In humans, (223)2 = 70,368,744,000,000 chromosomally different zygotes are possible
If crossing-over occurs only once
(423)2, or 4,951,760,200,000,000,000,000,000,000 genetically different zygotes are possible
Meiosis & Sexual Reproduction

25. Figure 13.10 The independent assortment of homologous chromosomes in meiosis
Key
Maternal set of
chromosomes
Paternal set of
Possibility 1
Two equally probable
arrangements of
chromosomes at
metaphase I
Possibility 2
Metaphase II
Daughter
cells
Combination 1
Combination 2
Combination 3
Combination 4
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

26. Crossing over further increases genetic variability

27. Biology, 9th ed,Sylvia Mader
Chapter 10
Meiosis vs. Mitosis
Meiosis
Requires two nuclear divisions
Chromosomes synapse and cross over
Centromeres survive Anaphase I
Halves chromosome number
Produces four daughter nuclei
Produces daughter cells genetically different from parent and each other
Used only for sexual reproduction
Mitosis
Requires one nuclear division
Chromosomes do not synapse nor cross over
Centromeres dissolve in mitotic anaphase
Preserves chromosome number
Produces two daughter nuclei
Produces daughter cells genetically identical to parent and to each other
Used for asexual reproduction and growth
Meiosis & Sexual Reproduction

28. PARENT CELL (before chromosome replication) Site of crossing over
MITOSIS
MEIOSIS
PARENT CELL (before chromosome replication)
Site of crossing over
MEIOSIS I
PROPHASE
PROPHASE I
Tetrad formed by synapsis of
homologous chromosomes
Duplicated chromosome (two sister chromatids)
Chromosome replication
Chromosome replication
2n = 4
Chromosomes align at the metaphase plate
Tetrads align at the
Metaphase plate
METAPHASE
METAPHASE I
ANAPHASE I
TELOPHASE I
ANAPHASE TELOPHASE
Sister chromatids separate during anaphase
Homologous chromosomes separate during anaphase I; sister chromatids remain together
Haploid n = 2
Daughter cells of meiosis I
2n = 4
2n = 4
No further chromosomal replication; sister chromatids separate during anaphase II
MEIOSIS II
Daughter cells of mitosis
Haploid
n = 2 n n n n
Daughter cells of meiosis II
Figure 8.15
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

29. Changes in Chromosome Number
Euploid is the correct number of chromosomes in a species.
Aneuploid is change in the chromosome number
Results from nondisjunction
Monosomy - only one of a particular type of chromosome,
Trisomy - three of a particular type of chromosome

30. Changes in Chromosome pair of homologous chromosomes pair of
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
pair of
homologous
chromosomes
pair of
homologous
chromosomes
Meiosis I
nondisjunction
normal
nondisjunction
Meiosis II
normal
Fertilization
Zygote 2n 2n
2n + 1
2n - 1
2n + 1
2n + 1
2n - 1
2n - 1 a. b.

31. Trisomy
Trisome 21
Occurs when an individual has three of a particular type of chromosome
The most common autosomal trisomy seen among humans
Also called Down syndrome
Recognized by these characteristics:
short stature
eyelid fold
flat face
stubby finger
wide gap between first and second toes

32. a: © Jose Carrilo/PhotoEdit; b: © CNRI/SPL/Photo Researchers
Trisomy 21
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
extra chromosome 21 a. b.
a: © Jose Carrilo/PhotoEdit; b: © CNRI/SPL/Photo Researchers

33. Changes in Sex Chromosome
Result from inheriting too many or too few X or Y chromosomes
Nondisjunction during oogenesis or spermatogenesis
Turner syndrome (XO)
Female with single X chromosome
Short, with broad chest and widely spaced nipples
Can be of normal intelligence and function with hormone therapy
Klinefelter syndrome (XXY) – a male
Male with underdeveloped testes and prostate; some breast overdevelopment
Long arms and legs; large hands
Near normal intelligence unless XXXY, XXXXY, etc.
No matter how many X chromosomes, presence of Y renders individual male

34. Changes in Chromosome Structure
Changes in chromosome structure include:
Deletions
One or both ends of a chromosome breaks off
Two simultaneous breaks lead to loss of an internal segment
Duplications
Presence of a chromosomal segment more than once in the same chromosome
Translocations
A segment from one chromosome moves to a non-homologous chromosome
Follows breakage of two nonhomologous chromosomes and improper re-assembly

35. Changes in Chromosome Structure
Duplication
A segment of a chromosome is repeated in the same chromosome
Inversion
Occurs as a result of two breaks in a chromosome
The internal segment is reversed before re-insertion
Genes occur in reverse order in inverted segment

36. 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

37. Types of Chromosomal Mutation
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a a b b + h
deletion
lost c c d d e e f f g g h a. b.
b: Courtesy The Williams Syndrome Association

38. Types of Chromosomal Mutation
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a s a s b t b t c c u u d
translocation v d v e w e w x x f f g y y g z h z h a. b.
b: American Journal of Human Genetics by N. B. Spinner. Copyright 1994 by Elsevier Science & Technology Journals. Reproduced with permission of Elsevier Science & Technology Journals in the format Textbook via Copyright Clearance Center