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Slide 1
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
PowerPoint® Lecture Presentations for
BiologyEighth Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp
Chapter 13
Meiosis and Sexual Life Cycles
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Slide 2 Key Terms and Definitions 1
• Genome _______________________________________
• Chromosome ___________________________________
• Gene __________________________________________
• Locus _________________________________________
• Genotype ______________________________________
• Phenotype _____________________________________
• Genetics _______________________________________
• Heredity _______________________________________
• Variation ______________________________________Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
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Slide 3 Fig. 16-21b
30-nm fiber
Chromatid (700 nm)
Loops Scaffold
300-nm fiber
Replicated chromosome (1,400 nm)
30-nm fiber Looped domains (300-nm fiber)
Metaphase chromosome
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Slide 4
DNA double helix (2 nm in diameter)
Nucleosome(10 nm in diameter)
Histones Histone tailH1
DNA, the double helix Histones Nucleosomes, or “beads on a string” (10-nm fiber)
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Slide 5 Fig. 5-28Sugar-phosphatebackbones
3' end
3' end
3' end
3' end
5' end
5' end
5' end
5' end
Base pair (joined byhydrogen bonding)
Old strands
Newstrands
Nucleotideabout to beadded to anew strand
Two polynucleotides spiraling around an imaginary axis form a Double Helix
What is meant by Antiparallel?
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Slide 6 Fig. 13-3APPLICATION
TECHNIQUE
Pair of homologousreplicated chromosomes
5 µm
Centromere
Sisterchromatids
Metaphasechromosome
• Human somatic cells –___ pairs of chromosomes
•The two chromosomes in each pair = ____________
• Are these chromosomes identical?
• A karyotype - an ordered display of the pairs of chromosomes from a cell
• What information can you get from a karyotype?
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Slide 7
Which of the following illustrate genotype? Phenotype?
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Nucleotide #17 - Adenine (A) is replaced by Thymine (T), resulting in a Val for Glu substitution at amino acid #6.
A BRCA1mutation
Breast Cancer Cell
DNA inherited by organisms lead to specific traits
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Slide 8 Key Terms and Definitions 2
• Life cycle ______________________________________
• Genetic inheritance _____________________________
• Asexual reproduction ____________________________
• Clone _________________________________________
• Sexual reproduction _____________________________
• Gametes _______________________________________
• Fertilization ____________________________________
• Somatic cells ___________________________________
• Allele _________________________________________
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
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Slide 9 Fig. 13-2
(a) Hydra (b) Redwoods
Parent
Bud
0.5 mm
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Slide 10 Fig. 13-6
KeyHaploid (n)Diploid (2n)
n nGametes
nn n
Mitosis
MEIOSIS FERTILIZATION
MEIOSIS
2n 2nZygote2n
MitosisDiploidmulticellularorganism
Animals
Spores
Diploidmulticellularorganism(sporophyte)
Plants and some algae
2n
Mitosis
Gametes
Mitosisn
n n
Zygote
FERTILIZATION
nn
nMitosis
Zygote
Most fungi and some protists
MEIOSIS FERTILIZATION
2n
Gametes
n
n
Mitosis
Haploid multi-cellular organism(gametophyte)
Haploid unicellular ormulticellular organism
Sexual Life Cycles
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Slide 11 Fig. 13-5Key
Haploid (n)Diploid (2n)
Haploid gametes (n = 23)Egg (n)
Sperm (n)
MEIOSIS FERTILIZATION
Ovary Testis
Diploidzygote(2n = 46)
Mitosis anddevelopment
Multicellular diploidadults (2n = 46)
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Slide 12
• The sex chromosomes are called X and Y
• Human females have a homologous pair of X chromosomes (XX)
• Human males have one X and one Y chromosome
• The 22 pairs of chromosomes that do not determine sex are called autosomes
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
The Animal Life Cycle
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Slide 13
• A diploid cell (2n) has two sets of chromosomes
• n = # of chromosomes in a gametes
• For humans, the diploid number is 46 (2n = 46)
(Fruit flies 2n = 8, Dogs 2n = 78)
Polyploidy = more than 2 sets of chromosomes (common in plants)
Are humans ever polyploids?
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
The Animal Life Cycle
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Slide 14 Fig. 13-4
KeyMaternal set ofchromosomes (n = 3)Paternal set ofchromosomes (n = 3)
2n = 6
Label the followingdiagram
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Slide 15
• A gamete (sperm or egg) contains a single set of chromosomes, and is haploid (n)
• For humans, the haploid number is 23 (n = 23)
• Each set of 23 consists of 22 autosomes and a single 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
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
The Animal Life Cycle
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Slide 16
• Fertilization is the union of gametes (the sperm and the egg)
• The fertilized egg is called a zygote and has one set of chromosomes from each parent
• The zygote produces somatic cells by _______ and develops into an adult
The Animal Life Cycle
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
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Slide 17 Fig. 13-5Key
HaploidDiploid Egg (n)
Sperm (n)
MEIOSIS FERTILIZATION
Ovary Testis
Diploidzygote
Mitosis anddevelopment
Multicellular diploidadults (2n = 46)
Key Concept:Much of ourinheritablevariationresults fromchanges to theparent’s DNA that occur during meiosis
Individualeggs and spermare different fromeach other and from the parent –therefore, soare siblings
What’s the differencebetween fraternal andidentical twins?
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Slide 18 The BIG PICTURE of Meiosis
• One Interphase just like Mitosis• G1, S-Phase, G2
• diploid 46 chromosomes replicate to form 92 sisters joined in pairs
• Followed by Two Cell Divisions instead of One• In meiosis I, homologous chromosomes separate resulting in two
haploid daughters with 46 sisters joined in 23 pairs
• it is called the reductional division
• In meiosis II, sister chromatids separate resulting in four haploid daughters with 23 unjoined chromosomes (much like mitosis)
• it is called the equational division
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
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Slide 19 Fig. 13-7-3Interphase
Homologous pair of chromosomesin diploid parent cell
Chromosomesreplicate
Homologous pair of replicated chromosomes
Sisterchromatids Diploid cell with
replicated chromosomes
Meiosis I
Homologouschromosomesseparate
1
Haploid cells withreplicated chromosomes
Meiosis II
2 Sister chromatidsseparate
Haploid cells with unreplicated chromosomes
reductional division
equational division
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Slide 20
Remind me what prophase is again........
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Slide 21
Metaphase I
Fig. 13-8a
Prophase I Anaphase I Telophase I andCytokinesis
Centrosome(with centriole pair)
Sisterchromatids Chiasmata
Spindle
Homologouschromosomes
Fragmentsof nuclearenvelope
Centromere(with kinetochore)
Metaphaseplate
Microtubuleattached tokinetochore
Sister chromatidsremain attached
Homologouschromosomesseparate
Cleavagefurrow
What are chiasmata?
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Slide 22
Remind me what telophase is again........
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Slide 23 Fig. 13-8d
Prophase II Metaphase II Anaphase II Telophase II andCytokinesis
Sister chromatidsseparate Haploid daughter cells
forming
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Slide 24 Fig. 13-7-3Interphase
Homologous pair of chromosomesin diploid parent cell
Chromosomesreplicate
Homologous pair of replicated chromosomes
Sisterchromatids Diploid cell with
replicated chromosomes
Meiosis I
Homologouschromosomesseparate
1
Haploid cells withreplicated chromosomes
Meiosis II
2 Sister chromatidsseparate
Haploid cells with unreplicated chromosomes
Are chromosomes condensed duringInterphase?
Which of the 3 stages shown are different from mitosis? In what way?
Reductional division =
Equational division =
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Slide 25 A Comparison of Mitosis and Meiosis
• Mitosis conserves the number of chromosome sets, producing cells that are genetically identical to the parent cell
• Meiosis reduces the number of chromosomes sets from two (diploid) to one (haploid), producing cells that differ genetically from each other and from the parent cell
• The mechanism for separating sister chromatids is virtually identical in meiosis II and mitosis
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
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Slide 26 Fig. 13-9a
MITOSIS MEIOSIS
MEIOSIS I
Prophase I
Chiasma
Chromosomereplication
Homologouschromosomepair
Chromosomereplication
2n = 6
Parent cell
Prophase
Replicated chromosome
Metaphase Metaphase I
Anaphase ITelophase I
Haploidn = 3
Daughtercells of
meiosis I
MEIOSIS II
Daughter cells of meiosis IInnnn
2n2n
Daughter cellsof mitosis
AnaphaseTelophase
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Slide 27
• Three events are unique to meiosis, and all three occur in meiosis l:
Formation of tetrads at the metaphase plate
Synapsis (cohesion) and crossing over amongst 4 sisters
Separation of homologous chromosomes
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
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Slide 28 Fig. 13-UN2
F
H
tetrads
cohesions
homologouschromosomes
meiosis I
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Slide 29
Remember Our Key Concept:
• Much of our inheritable variation results from changes to the parent’s DNA that occur during meiosis
• These changes occur in both parents and are then combined at fertilization to create most of the variation that arises in each generation
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
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Slide 30 Concept 13.4: Genetic variation produced in sexual life cycles contributes to evolution
• Mutations (changes in an organism’s DNA) are the primary source of genetic diversity
• Mutations create different versions of genes called alleles (which reside on homologous chromosomes)
• Reshuffling of alleles during sexual reproduction produces genetic variation
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
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Slide 31 Origins of Genetic Variation Among Offspring
Three mechanisms contribute to genetic variation:
– Independent assortment of chromosomes
– Crossing over
– Random fertilization
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
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Slide 32 Possibility 1 Possibility 2
Two equally probablearrangements ofchromosomes at
metaphase I
Metaphase II
Daughtercells
Combination 1 Combination 2 Combination 3 Combination 4
Independent assortment of chromosomes
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Slide 33 Independent Assortment of Chromosomes
• Homologous pairs of chromosomes orient randomly at metaphase I of meiosis
• In independent assortment, each pair of chromosomes sorts maternal and paternal homologues into daughter cells independently of the other pairs
• The number of combinations possible when chromosomes assort independently into gametes is 2n, where n is the haploid number
• For humans (n = 23), there are more than 8 million (223) possible combinations of chromosomes
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
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Slide 34 Fig. 13-12-5Prophase Iof meiosis
Pair ofhomologs
Nonsisterchromatidsheld togetherduring synapsis
Chiasma
Centromere
Anaphase I
Anaphase II
Daughtercells
Recombinant chromosomes
TEM
Crossing over
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Slide 35 Crossing Over
• Crossing over produces recombinant chromosomes, which combine genes inherited from each parent
• Crossing over begins very early in prophase I, as homologous chromosomes pair up gene by gene
• In crossing over, homologous portions of two nonsister chromatids trade places
• Crossing over contributes to genetic variation by combining DNA from two parents into a single chromosome
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
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Slide 36 Random Fertilization
• Random fertilization adds to genetic variation because any sperm can fuse with any ovum (unfertilized egg)
• The fusion of two gametes (each with 8.4 million possible chromosome combinations from independent assortment) produces a zygote with any of about 70 trillion diploid combinations
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
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Slide 37 The Evolutionary Significance of Genetic Variation Within Populations
• Natural selection results in the accumulation of genetic variations favored by the environment
• Sexual reproduction contributes to the genetic variation in a population, which originates from mutations
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
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