chapter 9 · chapter 9 sexual reproduction and meiosis ... the photo below shows two chromosomes...

Chapter 9 Sexual Reproduction and Meiosis

Ultrasound: © Chad Ehlers/Glow Images

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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?


• 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


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


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

http://www.saddleback.edu/faculty/steh/bio20folder/Meiosis.mpg

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


2n=4

All photos © Ed Reschke

In Meiosis, DNA Replicates Once, but the Nucleus Divides Twice


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


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



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


metaphase I

Possibility B

Metaphase II


Figure 8.15_s3

Possibility A


metaphase I

Possibility B

Metaphase II

Gametes

Combination 3 Combination 4Combination 2Combination 1


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

https://search.yahoo.com/search?fr=mcafee&type=B211US636D20140409&p=nfl+half+time+show

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


Sperm cells form in the testes. Egg cells form in the ovaries.

Sperm contacting egg: © Francis Leroy, Biocosmos/Science Source

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


Section 9.5

• Identical twins: embryo splits in two• Each embryo then develops independently

Figure 9.10Identical twins: © Barbara Penoyar/Getty Images RF


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


Mutations in chromosome structure can have major effects on an organism.

Chromosomes: © Addenbrookes Hospital/Science Source

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

chapter 9 · chapter 9 sexual reproduction and meiosis ... the photo below shows two chromosomes...

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