Date post: | 02-Jun-2018 |
Category: |
Documents |
Upload: | minhnguyen |
View: | 217 times |
Download: | 0 times |
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 1/84
LECTURE PRESENTATIONS For CAMPBELL BIOLOGY, NINTH EDITION
Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson
© 2011 Pearson Education, Inc.
Lectures byErin Barley
Kathleen Fitzpatrick
Meiosis and Sexual
Life Cycles
Chapter 13
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 2/84
Overview: Variations on a Theme
• Living organisms are distinguished by theirability to reproduce their own kind
• Genetics is the scientific study of heredity andvariation
• Heredity is the transmission of traits from onegeneration to the next
• Variation is demonstrated by the differences inappearance that offspring show from parentsand siblings
© 2011 Pearson Education, Inc.
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 3/84
Figure 13.1
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 4/84
Concept 13.1: Offspring acquire genes fromparents by inheriting chromosomes
• In a literal sense, children do not inheritparticular physical traits from their parents
•
It is genes that are actually inherited
© 2011 Pearson Education, Inc.
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 5/84
Inheritance of Genes
• Genes are the units of heredity, and are madeup of segments of DNA
• Genes are passed to the next generation viareproductive cells called gametes (sperm andeggs)
• Each gene has a specific location called alocus on a certain chromosome
• Most DNA is packaged into chromosomes
© 2011 Pearson Education, Inc.
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 6/84
Comparison of Asexual and SexualReproduction
• In asexual reproduction , a single individualpasses genes to its offspring without the fusion
of gametes• A clone is a group of genetically identical
individuals from the same parent• In sexual reproduction , two parents give rise
to offspring that have unique combinations ofgenes inherited from the two parents
© 2011 Pearson Education, Inc.
Video: Hydra Budding
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 7/84
Figure 13.2
(a) Hydra (b) Redwoods
Bud
Parent
0.5 mm
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 8/84
Figure 13.2a
Bud
Parent
0.5 mm
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 9/84
Figure 13.2b
(b) Redwoods
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 10/84
Concept 13.2: Fertilization and meiosisalternate in sexual life cycles
• A life cycle is the generation-to-generationsequence of stages in the reproductive historyof an organism
© 2011 Pearson Education, Inc.
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 11/84
Sets of Chromosomes in Human Cells
• Human somatic cells (any cell other than agamete) have 23 pairs of chromosomes
• A karyotype is an ordered display of the pairsof chromosomes from a cell
• The two chromosomes in each pair are calledhomologous chromosomes , or homologs
• Chromosomes in a homologous pair are thesame length and shape and carry genescontrolling the same inherited characters
© 2011 Pearson Education, Inc.
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 12/84
Figure 13.3
Pair of homologousduplicated chromosomes
Centromere
Sisterchromatids
Metaphase
chromosome
5 m
APPLICATION
TECHNIQUE
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 13/84
Figure 13.3a
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 14/84
Figure 13.3b
Pair of homologousduplicated chromosomes
Centromere
Sisterchromatids
Metaphasechromosome
5 m
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 15/84
Figure 13.3c
5 m
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 16/84
• The sex chromosomes , which determine the sex of the individual, are called X and Y
• Human females have a homologous pair of Xchromosomes (XX)
• Human males have one X and one Ychromosome
• The remaining 22 pairs of chromosomes arecalled autosomes
© 2011 Pearson Education, Inc.
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 17/84
• Each pair of homologous chromosomes includesone chromosome from each parent
• The 46 chromosomes in a human somatic cellare two sets of 23: one from the mother and onefrom the father
• A diploid cell (2 n ) has two sets ofchromosomes
• For humans, the diploid number is 46 (2 n = 46)
© 2011 Pearson Education, Inc.
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 18/84
• In a cell in which DNA synthesis has occurred,each chromosome is replicated
• Each replicated chromosome consists of twoidentical sister chromatids
© 2011 Pearson Education, Inc.
Fi 13 4
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 19/84
Figure 13.4
Sister chromatids
of one duplicatedchromosome
Key
Maternal set of
chromosomes (n
3)Paternal set ofchromosomes ( n 3)
Key
2 n 6
Centromere
Two nonsisterchromatids ina homologous pair
Pair of homologouschromosomes(one from each set)
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 20/84
• A gamete (sperm or egg) contains a single setof chromosomes, and is haploid (n )
• For humans, the haploid number is 23 ( n = 23)•
Each set of 23 consists of 22 autosomes and asingle sex chromosome• In an unfertilized egg (ovum), the sex
chromosome is X• In a sperm cell, the sex chromosome may be
either X or Y
© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 21/84
• Fertilization is the union of gametes (the spermand the egg)
•
The fertilized egg is called a zygote and hasone set of chromosomes from each parent• The zygote produces somatic cells by mitosis
and develops into an adult
Behavior of Chromosome Sets in theHuman Life Cycle
© 2011 Pearson Education, Inc.
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 22/84
• At sexual maturity, the ovaries and testesproduce haploid gametes
• Gametes are the only types of human cellsproduced by meiosis , rather than mitosis
• Meiosis results in one set of chromosomes ineach gamete
• Fertilization and meiosis alternate in sexual lifecycles to maintain chromosome number
© 2011 Pearson Education, Inc.
Figure 13 5
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 23/84
Figure 13.5 Key
Haploid ( n )Diploid (2 n )
Egg ( n )
Haploid gametes ( n 23)
Sperm ( n )
Ovary Testis
Mitosis anddevelopment
Diploidzygote
(2n
46)
Multicellular diploid
adults (2 n 46)
MEIOSIS FERTILIZATION
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 24/84
The Variety of Sexual Life Cycles
• The alternation of meiosis and fertilization iscommon to all organisms that reproducesexually
• The three main types of sexual life cycles differin the timing of meiosis and fertilization
© 2011 Pearson Education, Inc.
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 25/84
• Gametes are the only haploid cells in animals• They are produces by meiosis and undergo no
further cell division before fertilization•
Gametes fuse to form a diploid zygote thatdivides by mitosis to develop into a multicellularorganism
© 2011 Pearson Education, Inc.
Figure 13 6
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 26/84
Figure 13.6
KeyHaploid ( n )Diploid (2 n )
Gametes
MEIOSIS FERTILIZATION
Zygote
MitosisDiploidmulticellularorganism
(a) Animals
n
n
n
2 n 2 n 2 n 2 n
2 n
n n
n n
n
n
n
n
n n
MEIOSIS
MEIOSIS
FERTILIZATION
FERTILIZATION
Mitosis Mitosis
Mitosis
Mitosis Mitosis
GametesSpores
Gametes
Zygote
Zygote
Haploid multi-cellular organism(gametophyte)
Diploidmulticellularorganism(sporophyte)
Haploid unicellular ormulticellular organism
(b) Plants and some algae (c) Most fungi and some protists
Figure 13.6a
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 27/84
Figure 13.6a Key
Haploid ( n )Diploid (2 n )
Gametes
MEIOSIS FERTILIZATION
Zygote
MitosisDiploidmulticellularorganism
(a) Animals
n
2 n
n
n
2 n
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 28/84
• Plants and some algae exhibit an alternation ofgenerations
• This life cycle includes both a diploid andhaploid multicellular stage
• The diploid organism, called the sporophyte,makes haploid spores by meiosis
© 2011 Pearson Education, Inc.
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 29/84
• Each spore grows by mitosis into a haploidorganism called a gametophyte
• A gametophyte makes haploid gametes bymitosis
• Fertilization of gametes results in a diploidsporophyte
© 2011 Pearson Education, Inc.
Figure 13.6b K
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 30/84
g
2 n 2 n
n
MEIOSIS FERTILIZATION
Mitosis Mitosis
Mitosis
GametesSpores
Zygote
Haploid multi-cellular organism(gametophyte)
Diploidmulticellularorganism(sporophyte)
(b) Plants and some algae
n n
n
n
Haploid ( n )Diploid (2 n )
Key
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 31/84
• In most fungi and some protists, the onlydiploid stage is the single-celled zygote; thereis no multicellular diploid stage
• The zygote produces haploid cells by meiosis• Each haploid cell grows by mitosis into a
haploid multicellular organism• The haploid adult produces gametes by
mitosis
© 2011 Pearson Education, Inc.
Figure 13.6c K
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 32/84
KeyHaploid ( n )Diploid (2 n )
2 n
n n
n
n
n
MEIOSIS FERTILIZATION
Mitosis Mitosis
Gametes
Zygote
Haploid unicellular ormulticellular organism
(c) Most fungi and some protists
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 33/84
• Depending on the type of life cycle, eitherhaploid or diploid cells can divide by mitosis
• However, only diploid cells can undergomeiosis
• In all three life cycles, the halving and doublingof chromosomes contributes to geneticvariation in offspring
© 2011 Pearson Education, Inc.
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 34/84
Concept 13.3: Meiosis reduces the number ofchromosome sets from diploid to haploid
• Like mitosis, meiosis is preceded by thereplication of chromosomes
•
Meiosis takes place in two sets of celldivisions, called meiosis I and meiosis II• The two cell divisions result in four daughter
cells, rather than the two daughter cells in
mitosis• Each daughter cell has only half as many
chromosomes as the parent cell
© 2011 Pearson Education, Inc.
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 35/84
The Stages of Meiosis
• After chromosomes duplicate, two divisionsfollow
– Meiosis I (reductional division): homologs pairup and separate, resulting in two haploid
daughter cells with replicated chromosomes – Meiosis II (equational division) sister
chromatids separate• The result is four haploid daughter cells with
unreplicated chromosomes
© 2011 Pearson Education, Inc.
Figure 13.7-1 I h
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 36/84
Pair of homologouschromosomes indiploid parent cell
Duplicated pairof homologouschromosomes
Chromosomesduplicate
Sisterchromatids Diploid cell with
duplicatedchromosomes
Interphase
Figure 13.7-2 I t h
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 37/84
Pair of homologouschromosomes indiploid parent cell
Duplicated pairof homologouschromosomes
Chromosomesduplicate
Sisterchromatids Diploid cell with
duplicatedchromosomes
Homologouschromosomes separate
Haploid cells withduplicated chromosomes
Meiosis I
1
Interphase
Figure 13.7-3 I t h
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 38/84
Pair of homologouschromosomes indiploid parent cell
Duplicated pairof homologouschromosomes
Chromosomesduplicate
Sisterchromatids Diploid cell with
duplicatedchromosomes
Homologouschromosomes separate
Haploid cells withduplicated chromosomes
Sister chromatidsseparate
Haploid cells with unduplicated chromosomes
Interphase
Meiosis I
Meiosis II
2
1
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 39/84
• Meiosis I is preceded by interphase, when thechromosomes are duplicated to form sisterchromatids
• The sister chromatids are genetically identicaland joined at the centromere
• The single centrosome replicates, forming twocentrosomes
© 2011 Pearson Education, Inc.
BioFlix: Meiosis
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 40/84
• Division in meiosis I occurs in four phases – Prophase I – Metaphase I – Anaphase I – Telophase I and cytokinesis
© 2011 Pearson Education, Inc.
Figure 13.8
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 41/84
MEIOSIS I: Separates homologous chromosomes
Prophase I Metaphase I Anaphase I Telophase I andCytokinesis
Centrosome(with centriole pair)
Sisterchromatids
Chiasmata
Spindle
Homologouschromosomes
Fragmentsof nuclearenvelope
Duplicated homologouschromosomes (red and blue)pair and exchange segments;2 n 6 in this example.
Centromere(with kinetochore)
Metaphaseplate
Microtubuleattached tokinetochore
Chromosomes line upby homologous pairs.
Sister chromatidsremain attached
Homologouschromosomesseparate
Each pair of homologouschromosomes separates.
Cleavagefurrow
Two haploid cellsform; each chromosomestill consists of twosister chromatids.
MEIOSIS I: Separates sister chromatids
Prophase II Metaphase II Anaphase II Telophase II andCytokinesis
Sister chromatidsseparate
Haploid daughtercells forming
During another round of cell division, the sister chromatids finally separate;four haploid daughter cells result, containing unduplicated chromosomes.
Figure 13.8a
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 42/84
Prophase I Metaphase I Anaphase I Telophase I andCytokinesis
Centrosome(with centriole pair)
Sisterchromatids
Chiasmata
Spindle
Homologouschromosomes
Fragmentsof nuclearenvelope
Duplicated homologouschromosomes (red and blue)pair and exchange segments;2 n 6 in this example.
Centromere(with kinetochore)
Metaphaseplate
Microtubuleattached tokinetochore
Chromosomes line upby homologous pairs.
Sister chromatidsremain attached
Homologouschromosomesseparate
Each pair of homologouschromosomes separates.
Cleavagefurrow
Two haploidcells form; eachchromosomestill consistsof two sisterchromatids.
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 43/84
Prophase I • Prophase I typically occupies more than 90%
of the time required for meiosis•
Chromosomes begin to condense• In synapsis , homologous chromosomes
loosely pair up, aligned gene by gene
© 2011 Pearson Education, Inc.
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 44/84
•
In crossing over , nonsister chromatidsexchange DNA segments
• Each pair of chromosomes forms a tetrad, agroup of four chromatids
• Each tetrad usually has one or morechiasmata , X-shaped regions where crossingover occurred
© 2011 Pearson Education, Inc.
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 45/84
Metaphase I • In metaphase I, tetrads line up at the metaphase
plate, with one chromosome facing each pole• Microtubules from one pole are attached to the
kinetochore of one chromosome of each tetrad• Microtubules from the other pole are attached to
the kinetochore of the other chromosome
© 2011 Pearson Education, Inc.
Figure 13.8b
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 46/84
Prophase II Metaphase II Anaphase II Telophase II andCytokinesis
Sister chromatidsseparate
Haploid daughtercells forming
During another round of cell division, the sister chromatids finally separate;four haploid daughter cells result, containing unduplicated chromosomes.
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 47/84
Anaphase I • In anaphase I, pairs of homologous
chromosomes separate•
One chromosome moves toward each pole,guided by the spindle apparatus• Sister chromatids remain attached at the
centromere and move as one unit toward the
pole
© 2011 Pearson Education, Inc.
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 48/84
Telophase I and Cytokinesis • In the beginning of telophase I, each half of the
cell has a haploid set of chromosomes; eachchromosome still consists of two sisterchromatids
• Cytokinesis usually occurs simultaneously,forming two haploid daughter cells
© 2011 Pearson Education, Inc.
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 49/84
•
In animal cells, a cleavage furrow forms; inplant cells, a cell plate forms
• No chromosome replication occurs betweenthe end of meiosis I and the beginning ofmeiosis II because the chromosomes arealready replicated
© 2011 Pearson Education, Inc.
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 50/84
•
Division in meiosis II also occurs in four phases – Prophase II – Metaphase II – Anaphase II – Telophase II and cytokinesis
• Meiosis II is very similar to mitosis
© 2011 Pearson Education, Inc.
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 51/84
Prophase II • In prophase II, a spindle apparatus forms• In late prophase II, chromosomes (each still
composed of two chromatids) move towardthe metaphase plate
© 2011 Pearson Education, Inc.
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 52/84
Metaphase II • In metaphase II, the sister chromatids are
arranged at the metaphase plate• Because of crossing over in meiosis I, the two
sister chromatids of each chromosome are nolonger genetically identical
• The kinetochores of sister chromatids attach to
microtubules extending from opposite poles
© 2011 Pearson Education, Inc.
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 53/84
Anaphase II • In anaphase II, the sister chromatids separate• The sister chromatids of each chromosome
now move as two newly individualchromosomes toward opposite poles
© 2011 Pearson Education, Inc.
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 54/84
Telophase II and Cytokinesis • In telophase II, the chromosomes arrive at
opposite poles• Nuclei form, and the chromosomes begin
decondensing
© 2011 Pearson Education, Inc.
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 55/84
•
Cytokinesis separates the cytoplasm• At the end of meiosis, there are four daughter
cells, each with a haploid set of unreplicatedchromosomes
• Each daughter cell is genetically distinct fromthe others and from the parent cell
© 2011 Pearson Education, Inc.
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 56/84
A Comparison of Mitosis and Meiosis
•
Mitosis conserves the number of chromosomesets, producing cells that are geneticallyidentical to the parent cell
• Meiosis reduces the number of chromosomessets from two (diploid) to one (haploid),producing cells that differ genetically from eachother and from the parent cell
© 2011 Pearson Education, Inc.
Figure 13.9 MITOSIS
P rent cell
MEIOSIS
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 57/84
Prophase
Duplicatedchromosome
Chromosomeduplication
Parent cell
2n 6
Metaphase
AnaphaseTelophase
2n 2 n
Daughter cellsof mitosis
MEIOSIS I
MEIOSIS II
Prophase I
Metaphase I
Anaphase I
Telophase I
Haploidn 3
Chiasma
Chromosomeduplication Homologous
chromosome pair
Daughtercells of
meiosis I
Daughter cells of meiosis II n n n n
SUMMARY
Property Mitosis Meiosis
DNAreplication
Number ofdivisions
Synapsis ofhomologouschromosomes
Number ofdaughter cellsand geneticcomposition
Role in theanimal body
Occurs during interphase beforemitosis begins
One, including prophase, metaphase,anaphase, and telophase
Does not occur
Two, each diploid (2 n ) and geneticallyidentical to the parent cell
Enables multicellular adult to arise fromzygote; produces cells for growth, repair,and, in some species, asexual reproduction
Occurs during interphase before meiosis I begins
Two, each including prophase, metaphase, anaphase,and telophase
Occurs during prophase I along with crossing overbetween nonsister chromatids; resulting chiasmatahold pairs together due to sister chromatid cohesion
Four, each haploid ( n ), containing half as manychromosomes as the parent cell; genetically differentfrom the parent cell and from each other
Produces gametes; reduces number of chromosomesby half and introduces genetic variability among thegametes
Figure 13.9a
MITOSIS MEIOSIS
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 58/84
Prophase
Duplicatedchromosome
MITOSIS
Chromosomeduplication
Parent cell
2 n 6
Metaphase
AnaphaseTelophase
2 n 2 n
Daughter cellsof mitosis
MEIOSIS
MEIOSIS I
MEIOSIS II
Prophase I
Metaphase I
Anaphase I
Telophase I
Haploidn 3
Chiasma
Chromosomeduplication Homologous
chromosome pair
Daughtercells of
meiosis I
Daughter cells of meiosis II
n n n n
Figure 13.9b
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 59/84
SUMMARY
Property Mitosis Meiosis
DNAreplication
Number ofdivisions
Synapsis ofhomologouschromosomes
Number ofdaughter cellsand geneticcomposition
Role in theanimal body
Occurs during interphase beforemitosis begins
One, including prophase, metaphase,anaphase, and telophase
Does not occur
Two, each diploid (2 n ) and geneticallyidentical to the parent cell
Enables multicellular adult to arise fromzygote; produces cells for growth, repair,
and, in some species, asexual reproduction
Occurs during interphase before meiosis I begins
Two, each including prophase, metaphase, anaphase,and telophase
Occurs during prophase I along with crossing overbetween nonsister chromatids; resulting chiasmatahold pairs together due to sister chromatid cohesion
Four, each haploid ( n ), containing half as manychromosomes as the parent cell; genetically differentfrom the parent cell and from each other
Produces gametes; reduces number of chromosomesby half and introduces genetic variability among the
gametes
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 60/84
•
Three events are unique to meiosis, and allthree occur in meiosis l – Synapsis and crossing over in prophase I:
Homologous chromosomes physically connect
and exchange genetic information – At the metaphase plate, there are pairedhomologous chromosomes (tetrads), instead ofindividual replicated chromosomes
– At anaphase I, it is homologous chromosomes,instead of sister chromatids, that separate
© 2011 Pearson Education, Inc.
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 61/84
•
Sister chromatid cohesion allows sisterchromatids of a single chromosome to staytogether through meiosis I
• Protein complexes called cohesins are
responsible for this cohesion• In mitosis, cohesins are cleaved at the end ofmetaphase
• In meiosis, cohesins are cleaved along the
chromosome arms in anaphase I (separation ofhomologs) and at the centromeres in anaphase II(separation of sister chromatids)
© 2011 Pearson Education, Inc.
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 62/84
Concept 13.4: Genetic variation produced insexual life cycles contributes to evolution
• Mutations (changes in an organism’s DNA) arethe original source of genetic diversity
• Mutations create different versions of genescalled alleles
• Reshuffling of alleles during sexual reproductionproduces genetic variation
© 2011 Pearson Education, Inc.
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 63/84
Origins of Genetic Variation AmongOffspring
• The behavior of chromosomes during meiosisand fertilization is responsible for most of thevariation that arises in each generation
• Three mechanisms contribute to geneticvariation
– Independent assortment of chromosomes
– Crossing over – Random fertilization
© 2011 Pearson Education, Inc.
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 64/84
I ndependent Assortment of Chromosomes
•
Homologous pairs of chromosomes orientrandomly at metaphase I of meiosis• In independent assortment, each pair of
chromosomes sorts maternal and paternalhomologues into daughter cells independentlyof the other pairs
© 2011 Pearson Education, Inc.
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 65/84
•
The number of combinations possible whenchromosomes assort independently intogametes is 2 n , where n is the haploid number
• For humans ( n = 23), there are more than 8million (2 23 ) possible combinations ofchromosomes
© 2011 Pearson Education, Inc.
Figure 13.10-1
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 66/84
Possibility 1 Possibility 2
Two equally probablearrangements ofchromosomes at
metaphase I
Figure 13.10-2
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 67/84
Possibility 1 Possibility 2
Two equally probablearrangements ofchromosomes at
metaphase I
Metaphase II
Figure 13.10-3
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 68/84
Possibility 1 Possibility 2
Two equally probablearrangements ofchromosomes at
metaphase I
Metaphase II
Daughtercells
Combination 1 Combination 2 Combination 3 Combination 4
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 69/84
Crossing Over
•
Crossing over produces recombinantchromosomes , which combine DNA inheritedfrom each parent
• Crossing over begins very early in prophase I,as homologous chromosomes pair up gene bygene
© 2011 Pearson Education, Inc.
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 70/84
•
In crossing over, homologous portions of twononsister chromatids trade places• Crossing over contributes to genetic variation
by combining DNA from two parents into asingle chromosome
© 2011 Pearson Education, Inc.
Figure 13.11-1 Prophase I of meiosis
Nonsister chromatidsheld together
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 71/84
of meiosis held togetherduring synapsis
Pair of homologs
Figure 13.11-2 Prophase I of meiosis
Nonsister chromatidsheld together
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 72/84
of meiosis held togetherduring synapsis
Pair of homologs
Chiasma
Centromere
TEM
Figure 13.11-3 Prophase I of meiosis
Nonsister chromatidsheld together
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 73/84
of meiosis held togetherduring synapsis
Pair of homologs
Chiasma
Centromere
TEM
Anaphase I
Figure 13.11-4 Prophase I of meiosis
Nonsister chromatidsheld together
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 74/84
of meiosis held togetherduring synapsis
Pair of homologs
Chiasma
Centromere
TEM
Anaphase I
Anaphase II
Figure 13.11-5 Prophase I of meiosis
Nonsister chromatidsheld together
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 75/84
held togetherduring synapsis
Pair of homologs
Chiasma
Centromere
TEM
Anaphase I
Anaphase II
Daughtercells
Recombinant chromosomes
Figure 13.11a
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 76/84
Chiasma
Centromere
TEM
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 77/84
Random F er til ization
•
Random fertilization adds to genetic variationbecause any sperm can fuse with any ovum(unfertilized egg)
• The fusion of two gametes (each with 8.4million possible chromosome combinationsfrom independent assortment) produces azygote with any of about 70 trillion diploidcombinations
© 2011 Pearson Education, Inc.
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 78/84
•
Crossing over adds even more variation• Each zygote has a unique genetic identity
© 2011 Pearson Education, Inc.
Animation: Genetic Variation
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 79/84
The Evolutionary Significance of GeneticVariation Within Populations
• Natural selection results in the accumulation ofgenetic variations favored by the environment
• Sexual reproduction contributes to the geneticvariation in a population, which originates frommutations
© 2011 Pearson Education, Inc.
Figure 13.12
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 80/84
200 m
Figure 13.UN01
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 81/84
Prophase I : Each homologous pair undergoes synapsisand crossing over between nonsister chromatids withthe subsequent appearance of chiasmata.
Metaphase I : Chromosomes line up as homologouspairs on the metaphase plate.
Anaphase I : Homologs separate from each other; sister
chromatids remain joined at the centromere.
Figure 13.UN02
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 82/84
F
H
Figure 13.UN03
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 83/84
Figure 13.UN04
8/11/2019 13 MeiosisAndSexualLifeCycle 13 Lecture Presentation
http://slidepdf.com/reader/full/13-meiosisandsexuallifecycle-13-lecture-presentation 84/84