Sylvia S

. Mad

er

Copyright © The McGraw Hill Companies Inc. Permission required for reproduction or display

PowerPoint® Lecture Slides are prepared by Dr. Isaac Barjis, Biology Instructor

BIOLOGY10th Edition

Meiosis & Sexual Reproduction

Chapter 10: pp. 169 - 188

1

egg

FERTILIZATIONMEIOSIS

MITOSIS

MITOSIS

sperm

n

n

2n

2n

2n

2n

zygote

haploid (n)n = 23

2n = 46diploid (2n)

SPERMATOGENESIS

OOGENESIS

Metamorphosisand maturation

Primaryspermatocyte

Primaryoocyte

zygote

egg

Secondaryoocyte

Meiosis II is completedafter entry of sperm

spermatids

sperm

Secondaryspermatocytes

Firstpolar body

Secondpolar body

fusion of spermnucleus andegg nucleus

sperm nucleus

2n

2n

2n

n

n

n

n

n

n

n

n

Meiosis I

Meiosis II

Meiosis I

Fertilizationcont'd

Meiosis II

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2

Outline

Reduction in Chromosome Number Homologous Pairs Meiosis Overview

Genetic Variation Crossing-Over Independent Assortment Fertilization

Phases of Meiosis Meiosis I Meiosis II

Meiosis Compared to Mitosis Human Life Cycle Changes in Chromosome Number and Structure

3

Meiosis: Halves the Chromosome Number

Special type of cell division

Used only for sexual reproduction

Halves the chromosome number prior to fertilization

Parents diploid

Meiosis produces haploid gametes

Gametes fuse in fertilization to form diploid zygote

Becomes the next diploid generation

4

Homologous Pairs of Chromosomes

In diploid body cells chromosomes occur in pairs Humans have 23 different types of chromosomes Diploid cells have two of each type Chromosomes of the same type are said to be

homologous They have the same length Their centromeres are positioned in the same place One came from the father (the paternal homolog) the other from

the mother (the maternal homolog) When stained, they show similar banding patterns A location on one homologue contains gene for the same trait that

occurs at this locus on the other homologue Although the genes may code for different variations of that trait Alternate forms of a gene are called alleles

5

Homologous Chromosomes

a. sister chromatids

homologous pairchromosome chromosome

Nonsisterchromatids duplicationduplication

centromere

kinetochore

paternal chromosome maternal chromosome

b.

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Animation

6

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7

Homologous Pairs of Chromosomes

Homologous chromosomes have genes controlling the same trait at the same position Each gene occurs in duplicate A maternal copy from the mother A paternal copy from the father

Many genes exist in several variant forms in a large population

Homologous copies of a gene may encode identical or differing genetic information

The variants that exist for a gene are called alleles An individual may have:

Identical alleles for a specific gene on both homologs (homozygous for the trait), or

A maternal allele that differs from the corresponding paternal allele (heterozygous for the trait)

8

Overview of Meiosis

n = 2 n = 2

2n = 4 2n = 4

MEIOSIS IHomologous pairs

synapse and then separate.

centrioles sister chromatidssynapsis

nucleoluscentromere

chromosomeduplication

MEIOSIS IISister chromatids separate,

becoming daughter chromosomes.

Four haploiddaughter cells

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10

Phases of Meiosis I: Prophase I & Metaphase I

Meiosis I (reductional division):Prophase I

Each chromosome internally duplicated (consists of two identical sister chromatids)

Homologous chromosomes pair up – synapsisPhysically align themselves against each other end

to endEnd view would show four chromatids – Tetrad

Metaphase IHomologous pairs arranged onto the metaphase

plate

11

Phases of Meiosis I: Anaphase I & Telophase I

Anaphase ISynapsis breaks upHomologous chromosomes separate from one

anotherHomologues move towards opposite polesEach is still an internally duplicate chromosome with

two chromatidsTelophase I

Daughter cells have one internally duplicate chromosome from each homologous pair

One (internally duplicate) chromosome of each type (1n, haploid)

12

Phases of Meiosis I: Cytokinesis I & Interkinesis

Cytokinesis ITwo daughter cellsBoth with one internally duplicate chromosome of

each typeHaploidMeiosis I is reductional (halves chromosome

number)

InterkinesisSimilar to mitotic interphaseUsually shorterNo replication of DNA

Animation

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14

Genetic Variation: Crossing Over

Meiosis brings about genetic variation in two key ways: Crossing-over between homologous chromosomes, and Independent assortment of homologous chromosomes

Crossing Over: Exchange of genetic material between nonsister chromatids

during meiosis I At synapsis, a nucleoprotein lattice (called the

synaptonemal complex) appears between homologues Holds homologues together Aligns DNA of nonsister chromatids Allows crossing-over to occur

Then homologues separate and are distributed to different daughter cells

15

Crossing Over

A

B

bB

C

c C

DD D

A Aa

b

B b

c

C c

dd d

a a

nucleoprotein lattice sister chromatidsof a chromosome

sister chromatidsof its homologue

chiasmata ofnonsisternhromatids1 and 3

Bivalentforms

b.

1 2 3 4 1 2 3 4 1 2 3 4

a. c. d.

Crossing-overhas occurred

Daughterchromosomes

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Courtesy Dr. D. Von Wettstein

Animation

16

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17

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

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19

Independent Assortment

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

20

Recombination

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

© American Images, Inc/Getty Images

21

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

22

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

23

Phases of Meiosis II: Similar to Mitosis

Metaphase II Overview

Unremarkable Virtually indistinguishable from mitosis of two haploid cells

Prophase II – Chromosomes condense Metaphase II – Chromosomes align at metaphase

plate Anaphase II

Centromere dissolves Sister chromatids separate and become daughter

chromosomes Telophase II and cytokinesis II

Four haploid cells All genetically unique

Animation

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25

Meiosis I & II in Plant Cells (Cont.)

Prophase IChromosomes have duplicated.

Homologous chromosomes pair duringsynapsis and crossing-over occurs.

Metaphase IHomologous pairs align

Independently at the metaphase plate.

Anaphase IHomologous chromosomes separate

and move toward the poles.

Prophase IICells have one chromosomefrom each homologous pair.

Metaphase IIChromosomes align

at the metaphase plate.

Anaphase IISister chromatids separate and

become daughter chromosomes.

kinetochore

MEIOSIS I

MEIOSIS II

Animal Cellat Interphase

centrosome hascentrioles

Plant Cellat Interphase

2n = 4

n = 2

n = 2

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

© Ed Reschke

26

Meiosis I & II in Plant Cells

Telophase IDaughter cells have one chromosome

from each homologous pair.

InterkinesisChromosomes still

consist of two chromatids.

Telophase IISpindle disappears, nuclei form,

and cytokinesis takes place.

Daughter cellsMeiosis results in fourhaploid daughter cells.

MEIOSIS I cont'd

MEIOSIS II cont'd

n = 2

n = 2

n = 2

n = 2

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

© Ed Reschke

Animation

27

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28

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

29

Meiosis Compared to Mitosis

Prophase ISynapsis and

crossing-over occur.

Metaphase IHomologous pairs align

independently at the metaphase plate.

Anaphase IHomologous chromosomes

separate and move towards the poles.

Prophase MetaphaseChromosomes align

at the metaphase plate.

AnaphaseSister chromatids separate and

become daughter chromosomes.

MEIOSIS I

MITOSIS

2n = 4

2n = 4

Telophase IDaughter cells are forming

and will go on to divide again.

TelophaseDaughter cellsare forming.

Sister chromatidsseparate and become

daughter chromosomes.

Two diploid daughter cells.Their nuclei are geneticallyidentical to the parent cell.

Four haploid daughter cells.Their nuclei are genetically

different from the parent cell.

MEIOSIS I cont'd MEIOSIS II

MITOSIS cont'd

Daughter cells

Daughter cells

n = 2

n = 2

n = 2

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Animation

30

Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.

31

Meiosis I Compared to Mitosis

32

Meiosis II Compared to Mitosis

33

Life Cycle Basics: Plants

Haploid multicellular “individuals” alternate with diploid multicellular “individuals”

The haploid individual: Known as the gametophyte May be larger or smaller than the diploid individual

The diploid individual: Known as the sporophyte May be larger or smaller than the haploid individual

Mosses are haploid most of their life cycle Ferns & higher plants have mostly diploid life cycles In fungi and most algae, only the zygote is diploid In plants gametes are produced by haploid individuals

Plants have both haploid and diploid phases in their life cycle

34

Life Cycle Basics: Animals

In familiar animals: “Individuals” are diploid; produce haploid

gametesOnly haploid part of life cycle is the gametesThe products of meiosis are always gametesMeiosis occurs only during gametogenesis

Production of sperm Spermatogenesis All four cells become sperm

Production of eggs Oogenesis Only one of four nuclei get cytoplasm

Becomes the egg or ovum Others wither away as polar bodies

35

The Human Life Cycle

Sperm and egg are produced by meiosis A sperm and egg fuse at fertilization Results in a zygote

The one-celled stage of an individual of the next generation Undergoes mitosis

Results in multicellular embryo that gradually takes on features determined when zygote was formed

All growth occurs as mitotic division As a result of mitosis, each somatic cell in body

Has same number of chromosomes as zygote Has genetic makeup determined when zygote was formed

36

The Human Life Cycle

egg

FERTILIZATIONMEIOSIS

MITOSIS

MITOSIS

sperm

n

n

2n

2n

2n

2n

zygote

haploid (n)n = 23

2n = 46diploid (2n)

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

SPERMATOGENESIS

OOGENESIS

Metamorphosisand maturation

Primaryspermatocyte

Primaryoocyte

zygote

egg

Secondaryoocyte

Meiosis II is completed

after entry of sperm

spermatids

sperm

Secondaryspermatocytes

Firstpolar body

Secondpolar body

fusion of spermnucleus andegg nucleus

sperm nucleus

2n

2n

2n

n

n

n

n

n

n

n

n

Meiosis I

Meiosis II

Meiosis I

Fertilizationcont'd

Meiosis II

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

37

Gametogenesis in Mammals

38

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

39

Changes in Chromosome

a. b.

pair ofhomologouschromosomes

2n 2n 2n + 1 2n + 1 2n + 1 2n - 1

normal

normal

pair ofhomologouschromosomes

Meiosis I

Meiosis II

Fertilization

Zygote

nondisjunction

nondisjunction

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2n - 12n - 1

40

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

41

Trisomy 21

a. b.

extra chromosome 21

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

a: © Jose Carrilo/PhotoEdit; b: © CNRI/SPL/Photo Researchers

42

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

43

Changes in Sex Chromosome

a. Turner syndrome b. Klinefelter syndrome

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

a: Courtesy UNC Medical Illustration and Photography; b: Courtesy Stefan D. Schwarz, http://klinefeltersyndrome.org

44

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

Animation

45

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46

Changes in Chromosome Structure

DuplicationA segment of a chromosome is repeated in the

same chromosomeInversion

Occurs as a result of two breaks in a chromosome

The internal segment is reversed before re-insertionGenes occur in reverse order in inverted segment

Animation

Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.

48

Types of Chromosomal Mutation

c. Inversion d. Translocation

b. Duplicationa. Deletion

+

abc

d

e

f

g

abcd

e

f

g

h

abc

de

f

g

ab

e

f

g

lmn

op

q

r

abcd

e

f

lmn

op

abc

de

f

g

abc

de

f

g

bc

d

e

f

g

g

h

q

r

de

a

c

d

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Animation

Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.

Animation

50

Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.

51

Types of Chromosomal Mutation

deletion lost

a. b.

+ h

a

b

c

d

e

f

g

h

a

b

c

d

e

f

g

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

b: Courtesy The Williams Syndrome Association

52

Types of Chromosomal Mutation

translocation

a. b.

a

b

c

d

e

f

g

h

s

t

u

v

w

x

y

z

a

b

c

d

e

f

g

h

s

t

u

v

w

x

y

z

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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

53

Review

Reduction in Chromosome Number Meiosis Overview Homologous Pairs

Genetic Variation Crossing-Over Independent Assortment Fertilization

Phases of Meiosis Meiosis I Meiosis II

Meiosis Compared to Mitosis Human Life Cycle Changes in Chromosome Number and Structure

Sylvia S

. Mad

er

Copyright © The McGraw Hill Companies Inc. Permission required for reproduction or display

PowerPoint® Lecture Slides are prepared by Dr. Isaac Barjis, Biology Instructor

BIOLOGY10th Edition

Meiosis & Sexual Reproduction

Chapter 10: pp. 169 - 188

54

egg

FERTILIZATIONMEIOSIS

MITOSIS

MITOSIS

sperm

n

n

2n

2n

2n

2n

zygote

haploid (n)n = 23

2n = 46diploid (2n)

SPERMATOGENESIS

OOGENESIS

Metamorphosisand maturation

Primaryspermatocyte

Primaryoocyte

zygote

egg

Secondaryoocyte

Meiosis II is completedafter entry of sperm

spermatids

sperm

Secondaryspermatocytes

Firstpolar body

Secondpolar body

fusion of spermnucleus andegg nucleus

sperm nucleus

2n

2n

2n

n

n

n

n

n

n

n

n

Meiosis I

Meiosis II

Meiosis I

Fertilizationcont'd

Meiosis II

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.