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Chapter 9 Sexual Reproduction and Meiosis
Ultrasound: © Chad Ehlers/Glow Images
Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.
What are the 2 forms of reproduction?
Section 9.1 Figure 9.1
1) Asexual2) Sexual
Human family: © Corbis RF; Amoeba reproducing by binary fission: © Carolina Biological Supply
Company/Phototake; Mother cat and kittens: © Jane Burton/Dorling Kindersley/Getty Images
Why Sex?
Section 9.1 Figure 9.2
• Genetic diversity • Increases chance to survive
Semen attack unsuspecting ovum
Figure 8.11
Pair of homologouschromosomes
Locus
Centromere
Sisterchromatids
One duplicatedchromosome
Homologous chromosomes
Diploid Cells Contain Two Homologous Sets of Chromosomes
Section 9.2 Figure 9.3
Most cells in a sexually reproducing organism have two sets of chromosomes: one from the father and one from the mother.
All karyotype photos: © CNRI/Science Source
Diploid Cells Contain Two Homologous Sets of Chromosomes
Section 9.2 Figure 9.4
Homologous pair:• look alike chromosomes• carry the same sequence of
genes for the same traits • ALLELES different versions
The photo below shows two chromosomes from one cell. Which statement is true?
A. Both came from theperson’s mother.B. The 1-2 pair is identicalto the 3-4 pair.C. 1 is identical to 2.D. The chromosomes havenot been replicated yet.
1 2 3 4
Flower: © Doug Sherman/Geofile/RF
Figure 8.12AHaploid gametes (n 23)
Egg cell
Sperm cell
Fertilization
n
n
Meiosis
Ovary Testis
Diploidzygote
(2n 46)2n
MitosisKey
Haploid stage (n)
Diploid stage (2n)Multicellular diploid
adults (2n 46)
Meiosis Overview
Section 9.3 Figure 9.6Human female karyotype: © James Cavallini/Science Source
Meiosis• scrambles alleles• halves the chromosome number
2n=4 n=2
n=2
MEIOSIS I MEIOSIS II
Figure 8.12B
A pair ofhomologouschromosomesin a diploidparent cell
A pair ofduplicatedhomologouschromosomes
Sisterchromatids
1 2 3
INTERPHASE MEIOSIS I MEIOSIS II
In Meiosis, DNA Replicates Once, but the Nucleus Divides Twice
Section 9.4 Figure 9.7
2n=4
All photos © Ed Reschke
In Meiosis, DNA Replicates Once, but the Nucleus Divides Twice
Section 9.4 Figure 9.7
n=2
All photos © Ed Reschke
Figure 8.13_3
Cleavagefurrow
Telophase I and Cytokinesis
Figure 8.13_4
Prophase II Metaphase II Anaphase II
MEIOSIS II: Sister chromatids separate
Sister chromatidsseparate
Haploid daughter
cells forming
Telophase IIand Cytokinesis
Interphase
Prophase I
• Synapsis
• Tetrad formation
• Crossing over
Meiosis I
Meiosis Generates Variability
Section 9.5 Figure 9.8
During crossing over, two homologous chromosomes exchange genetic material during prophase I.
Meiosis I
Figure 8.16
Coat-colorgenes
Eye-colorgenes
Brown Black
Meiosis
White Pink
Tetrad in parent cell
(homologous pair of
duplicated chromosomes)
Chromosomes of
the four gametes White coat (c);pink eyes (e)
Brown coat (C);black eyes (E)
EC
ec
e
E
E
ec
c
C
C
Crossing OverWhat are the results for the chromosomes after crossing over?
Meiosis I
Figure 8.17B_2
Separation of homologous
chromosomes at anaphase I3
C E
C e
Chiasma
c
c
E
e
C E
c e
Crossing OverMeiosis I
Figure 8.17B_3
Separation of chromatids atanaphase II andcompletion of meiosis
Parental type of chromosome
Recombinant chromosome
Recombinant chromosome
Parental type of chromosome
Gametes of four genetic types
C E
eC
4
Ec
c e
EC
eC
c E
c e
Crossing OverMeiosis I
Metaphase I
• Metaphase plate
• Independent assortment
• 2n 223 => 8 million
Meiosis I
Meiosis Generates Variability
Section 9.5 Figure 9.9
In independent assortment, chromosome pairs align randomly during metaphase I.
Meiosis I
Figure 8.15_s1
Possibility A
Two equally probablearrangements ofchromosomes at
metaphase I
Possibility B
Independent AssortmentMeiosis I
Figure 8.15_s2
Possibility A
Two equally probablearrangements ofchromosomes at
metaphase I
Possibility B
Metaphase II
Independent AssortmentMeiosis I
Figure 8.15_s3
Possibility A
Two equally probablearrangements ofchromosomes at
metaphase I
Possibility B
Metaphase II
Gametes
Combination 3 Combination 4Combination 2Combination 1
Independent AssortmentMeiosis I
Anaphase I
• Homologous chromosomes separate
• Sister chromatids attached
Meiosis I
Telophase I & Cytokinesis
• Cleavage furrow
• Cell Plate
• 2 cells
• Haploid
• Sister chromatids attached
Meiosis I
Half Time!
• Rest break
• Reformation of nucleus, nucleolus, etc.
• NO MORE DNA Replication!!!
• Temporary, if it occurs at all
Prophase II
• Same as prophase of mitosis
Meiosis II
Metaphase II
• Metaphase plate
• Line up single file
Meiosis II
Anaphase II
• Sister chromatids separate
Meiosis II
Telophase II & Cytokinesis
• 4 cells
• haploid
• variation
Meiosis II
Figure 8.14
Prophase
Metaphase
Duplicated
chromosome(two sister
chromatids)
MITOSIS
Parent cell
(before chromosome duplication)
Chromosomeduplication
Chromosomeduplication
Site of
crossing
over
2n 4
Chromosomes
align at the
metaphase plate
Tetrads (homologous
pairs) align at the
metaphase plate
Tetrad formed
by synapsis of
homologous
chromosomes
Metaphase I
Prophase I
MEIOSIS I
Anaphase
Telophase
Sister chromatids
separate duringanaphase
2n 2n
Daughter cells of mitosis
No further
chromosomalduplication;
sister
chromatidsseparate during
anaphase II
n n n n
Daughter cells of meiosis II
Daughter
cells ofmeiosis I
Haploid
n 2
Anaphase I
Telophase I
Homologous
chromosomesseparate during
anaphase I;
sister
chromatids
remain together
MEIOSIS II
Meiosis Produces Human Gametes
Section 9.8 Figure 9.15
Sperm cells form in the testes. Egg cells form in the ovaries.
Sperm contacting egg: © Francis Leroy, Biocosmos/Science Source
Meiosis Produces Human Gametes
Section 9.8 Figure 9.16
Meiosis Produces Human Gametes
Section 9.8 Figure 9.17
Spermatogenesis
• Spermatogenesis
• Puberty
• 4 potential sperm
• Acrosome cap
Mature Sperm
Oogenesis
• Oogenesis
• Prior to birth (7 month)• Arrested: Prophase I
• Puberty• Arrested: Metaphase II
• Fertilization• Completion of meiosis
• Polar bodies
Ovum development
Meiosis Generates Variability
Section 9.5
• Identical twins: embryo splits in two• Each embryo then develops independently
Figure 9.10Identical twins: © Barbara Penoyar/Getty Images RF
Meiosis Generates Variability
Section 9.5
Fraternal twins:two sperm cells fertilize two separate egg cells
Figure 9.10Fraternal twins: © Image Source Black/ Getty Images RF
Many sets of triplets consist of a “pair and a spare;” that is, two identical babies and one non-identical baby. Producing this arrangement requires ___ sperm and ___ eggs.
A. 2 … 2B. 1 … 3C. 3 … 1D. 2 … 3
Flower: © Doug Sherman/Geofile/RF
Karyotyping
Human Karyotypes
Figure 8.20A_s3
Nondisjunction
MEIOSIS I
MEIOSIS II
Normalmeiosis II
Gametes
Number ofchromosomes
Abnormal gametes
n 1 n 1 n 1 n 1
Nondisjunction
Figure 8.20B_s3
Normalmeiosis I
MEIOSIS I
MEIOSIS II
Nondisjunction
Abnormal gametes Normal gametes
n 1 n 1 n n
Nondisjunction
Nondisjunction
Nondisjuction & Fertilization
Figure 8.19A
Trisomy 21
Downs Syndrome & Maternal Age
Figure 8.23A
Deletion
Duplication
Inversion
Reciprocal translocation
Homologous
chromosomes Nonhomologouschromosomes
Chromosomal Alterations
Figure 8.23B
Chromosome 9
Chromosome 22 Reciprocaltranslocation
“Philadelphia chromosome”
Activated cancer-causing gene
Chromosomal AlterationsReciprocal translocation
Errors Also Occur Within Chromosomes
Section 9.7 Figure 9.14
Mutations in chromosome structure can have major effects on an organism.
Chromosomes: © Addenbrookes Hospital/Science Source
Klinefelter’s Syndrome
Klinefelter’s Syndrome
Turner’s Syndrome
XYY – Super Male
Number of chromosomalduplications
Number of cell divisions
Number of daughter cells
produced
Number of chromosomes in
the daughter cells
How the chromosomes line
up during metaphase
Genetic relationship of the
daughter cells to the parent cell
Functions performed in thehuman body
Mitosis Meiosis
