1
Sylvia S. Mader
BIOLOGY Edition 10th
n n n n n 2n 2n 2n egg sperm oocyte Primary oocyte
zygote 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
-
2n
zygote Hill Hill Companies, Inc. Permission required for reproduction 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 MITOSIS
MEIOSIS
Reproduction 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
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
2 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
3 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
4 Homologous Chromosomes
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a. sister chromatids
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 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)
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 zygotes 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
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
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 Animal 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: 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
33 Life Cycle Basics: Animals
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 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
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 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
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 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
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 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
42 Changes in Sex Chromosome
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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- homologous chromosome
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 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
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