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1

Sylvia S. Mader

BIOLOGY Edition 10th

n n n n n 2n 2n 2n egg oocyte Primary oocyte

Primary spermatids Secondary Secondary spermatocyte spermatocytes after entry of entry sperm after II is completed

n n n

First

Second polar polar body polar polar body

sperm nucleus sperm fusion of sperm nucleus and egg nucleus Meiosis II Fertilization cont'd Meiosis I Meiosis II Metamorphosis and maturation Meiosis I

188

-

2n

zygote Hill Hill Companies, Inc. Permission required for or display. -

FERTILIZATION

MITOSIS n sperm

2n

n Copyright Copyright © The McGraw egg n = 23 = n 2n = 46 = 2n pp. 169 169 pp. haploid (n) haploid

diploid (2n) diploid

2n

MEIOSIS

Reproduction 2n

Meiosis & Sexual & Sexual Meiosis

Chapter 10: Chapter PowerPoint® Lecture Slides are prepared by Dr. Isaac Barjis, Instructor Biology Barjis, Isaac Dr. by prepared are Slides Lecture PowerPoint® Copyright © The McGraw Hill Companies Inc. Permission required for required Copyright Permission reproductionHill Companies or display Inc. McGraw© The

Outline

 Reduction in Number  Homologous Pairs  Meiosis Overview   Crossing-Over  Independent Assortment  Fertilization  Phases of Meiosis  Meiosis I  Meiosis II  Meiosis Compared to Mitosis  Human Cycle  Changes in Chromosome Number and Structure

2 Meiosis: Halves the Chromosome Number

 Special type of division

 Used only for

 Halves the chromosome number prior to fertilization

 Parents diploid

 Meiosis produces haploid

 Gametes fuse in fertilization to form diploid zygote

 Becomes the next diploid generation

3 Homologous Pairs of

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

4 Homologous Chromosomes

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a. sister

Nonsister duplication chromatids duplication

kinetochore

centromere

chromosome homologous pair chromosome

paternal chromosome maternal chromosome

b.

5 Animation

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6 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  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)

7 Overview of Meiosis

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Four haploid daughter cells centrioles nucleolus sister chromatids synapsis centromere

chromosome duplication

2n = 4 2n = 4

n = 2 n = 2 MEIOSIS I MEIOSIS II Homologous pairs Sister chromatids separate, synapse and then separate. becoming daughter chromosomes.

8 Animation

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 Meiosis I (reductional division):  Prophase I

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

 Homologous chromosomes pair up – synapsis

 Physically align themselves against each other end to end

 End view would show four chromatids – Tetrad  Metaphase I

 Homologous pairs arranged onto the metaphase plate

10 Phases of Meiosis I: Anaphase I & Telophase I

 Anaphase I  Synapsis breaks up  Homologous chromosomes separate from one another  Homologues move towards opposite poles  Each is still an internally duplicate chromosome with two chromatids  Telophase I  Daughter cells have one internally duplicate chromosome from each homologous pair  One (internally duplicate) chromosome of each type (1n, haploid)

11 Phases of Meiosis I: Cytokinesis I & Interkinesis

 Cytokinesis I  Two daughter cells  Both with one internally duplicate chromosome of each type  Haploid  Meiosis I is reductional (halves chromosome number)  Interkinesis  Similar to mitotic interphase  Usually shorter  No replication of DNA

12 Animation

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 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

14 Crossing Over

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nucleoprotein lattice sister chromatids sister chromatids of a chromosome of its homologue

A A a a A a

B B b b

B b chiasmata of nonsister nhromatids 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 Crossing-over Daughter forms has occurred chromosomes

a. b. c. d.

Courtesy Dr. D. Von Wettstein

15 Animation

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16 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

17 Animation

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19 Recombination

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© American Images, Inc/Getty Images

20 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 are possible

 If crossing-over occurs only once

23  (4 )2, or 4,951,760,200,000,000,000,000,000,000 genetically different zygotes are possible

21 Genetic Variation: Significance

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

adapt to that environment

22 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

23 Animation

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Plant Cell at Interphase

centrosome has centrioles

kinetochore 2n = 4 Prophase I Metaphase I Anaphase I Chromosomes have duplicated. Homologous pairs align Homologous chromosomes separate Cell Homologous chromosomes pair during Independently at the metaphase plate. and move toward the poles. at Interphase synapsis and crossing-over occurs.

MEIOSIS I

n = 2

n = 2 Prophase II Metaphase II Anaphase II Cells have one chromosome Chromosomes align Sister chromatids separate and from each homologous pair. at the metaphase plate. become daughter chromosomes.

MEIOSIS II

© Ed Reschke

25 Meiosis I & II in Plant Cells

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n = 2 Telophase I Interkinesis Daughter cells have one chromosome Chromosomes still n = 2 from each homologous pair. consist of two chromatids.

MEIOSIS I cont'd

n = 2

n = 2 Telophase II Daughter cells Spindle disappears, nuclei form, Meiosis results in four and cytokinesis takes place. haploid daughter cells.

MEIOSIS II cont'd

© Ed Reschke

26 Animation

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27 Meiosis vs. Mitosis

 Meiosis  Mitosis  Requires two nuclear  Requires one nuclear divisions division  Chromosomes synapse and  Chromosomes do not cross over synapse nor cross over  Centromeres survive  Centromeres dissolve in Anaphase I mitotic anaphase  Halves chromosome  Preserves chromosome number number  Produces four daughter  Produces two daughter nuclei nuclei  Produces daughter cells  Produces daughter cells genetically different from genetically identical to parent and each other parent and to each other  Used only for sexual  Used for asexual reproduction reproduction and growth

28 Meiosis Compared to Mitosis

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Telophase I Daughter cells are forming and will go on to divide again. n = 2

Daughter cells Sister chromatids separate and become 2n = 4 daughter chromosomes. Four haploid daughter cells. Their nuclei are genetically n = 2 Prophase I Metaphase I Anaphase I n = 2 different from the parent cell. Synapsis and Homologous pairs align Homologous chromosomes crossing-over occur. independently at the metaphase plate. separate and move towards the poles. MEIOSIS I MEIOSIS I cont'd MEIOSIS II

Daughter cells

Telophase Two diploid daughter cells. 2n = 4 Their nuclei are genetically Daughter cells identical to the parent cell. Prophase Metaphase Anaphase are forming. Chromosomes align Sister chromatids separate and at the metaphase plate. become daughter chromosomes. MITOSIS cont'd MITOSIS

29 Animation

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30 Meiosis I Compared to Mitosis

31 Meiosis II Compared to Mitosis

32 Life Cycle Basics:

 Haploid multicellular “individuals” alternate with diploid multicellular “individuals”  The haploid individual:  Known as the  May be larger or smaller than the diploid individual  The diploid individual:  Known as the  May be larger or smaller than the haploid individual  are haploid most of their life cycle  & higher plants have mostly diploid life cycles  In fungi and most , only the zygote is diploid  In plants gametes are produced by haploid individuals  Plants have both haploid and diploid phases in their life cycle

33 Life Cycle Basics:

 In familiar animals:  “Individuals” are diploid; produce haploid gametes  Only haploid part of life cycle is the gametes  The products of meiosis are always gametes  Meiosis occurs only during  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

34 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 that gradually takes on features determined when zygote was formed  All growth occurs as mitotic division  As a result of mitosis, each in body  Has same number of chromosomes as zygote  Has genetic makeup determined when zygote was formed

35 The Human Life Cycle

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MITOSIS 2n 2n

2n

MITOSIS

2n

zygote

2n = 46 diploid (2n) MEIOSIS FERTILIZATION haploid (n) n = 23 n

n egg sperm

36 Gametogenesis in Mammals

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SPERMATOGENESIS Primary spermatocyte 2n Meiosis I

Secondary spermatocytes n Meiosis II

spermatids n

Metamorphosis and maturation sperm n

OOGENESIS Primary oocyte 2n

Meiosis I

First polar body n Secondary oocyte n

Meiosis II

Meiosis II is completed Second after entry of sperm polar body n Fertilization egg cont'd n sperm nucleus n

fusion of sperm nucleus and zygote egg nucleus 2n

37 Changes in Chromosome Number

 Euploid is the correct number of chromosomes in a .  Aneuploid is change in the chromosome number  Results from nondisjunction  Monosomy - only one of a particular type of chromosome,  - three of a particular type of chromosome

38 Changes in Chromosome

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pair of pair of homologous homologous chromosomes 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.

39 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

40 Trisomy 21

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extra chromosome 21

a. b.

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

41 Changes in Chromosome

 Result from inheriting too many or too few X or Y chromosomes  Nondisjunction during oogenesis or spermatogenesis  Turner syndrome (XO)  with single  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

42 Changes in

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

43 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-

 Follows breakage of two nonhomologous chromosomes and improper re-assembly

44 Animation

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45 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

46 Animation

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a a a b b b b c c c c + a d d d d e e e e d f f f e g g g f g a. Deletion b. Duplication

a a a a b b b l b l c m c m c d d n d n c d 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

48 Animation

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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.

50 Types of Chromosomal Mutation

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a a b b

+ h deletion c c lost

d d

e e

f f

g g

h

a. b. b: Courtesy The Williams Syndrome Association

51 Types of Chromosomal Mutation

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a s a s b t b t c c u u translocation d v d v

e w e w

f x f x

g y y g

h z z h

a. b. b: American Journal of Human 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

52 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

53

54

Sylvia S. Mader

BIOLOGY Edition 10th

n n n n n 2n 2n egg 2n sperm oocyte zygote Primary oocyte Primary spermatids Secondary Secondary spermatocyte spermatocytes after entry of entry sperm after Meiosis II is completed

n n n

First

Second polar polar body polar polar body

sperm nucleus sperm fusion of sperm nucleus and egg nucleus Meiosis II Fertilization cont'd Meiosis I Meiosis II Metamorphosis and maturation Meiosis I OOGENESIS SPERMATOGENESIS

188

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Hill Hill Companies, Inc. Permission required for reproduction or display. - 2n

zygote

FERTILIZATION

MITOSIS n sperm pp. 169 169 pp.

2n

Copyright Copyright © The McGraw

n egg n = 23 = n 2n = 46 = 2n haploid (n) haploid diploid (2n) diploid

2n Reproduction

MITOSIS

MEIOSIS

2n

Meiosis & Sexual & Sexual Meiosis

Chapter 10: Chapter PowerPoint® Lecture Slides are prepared by Dr. Isaac Barjis, Biology Instructor Biology Barjis, Isaac Dr. by prepared are Slides Lecture PowerPoint® Copyright © The McGraw Hill Companies Inc. Permission required for required Copyright Permission reproductionHill Companies or display Inc. McGraw© The