chapter 13: meiosis and sexual life cycles
DESCRIPTION
Chapter 13: Meiosis and Sexual Life Cycles. Parent. Bud. 0.5 mm. Figure 13.2 The asexual reproduction of a hydra. APPLICATION A karyotype is a display of condensed chromosomes arranged in pairs. Karyotyping can be used to screen for abnormal numbers of chromosomes or - PowerPoint PPT PresentationTRANSCRIPT
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Chapter 13:
Meiosis and Sexual Life Cycles
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 13.2 The asexual reproduction of a hydra
Parent
Bud
0.5 mm
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 13.3 Preparing a Karyotype
APPLICATION A karyotype is a display of condensed chromosomes arranged in pairs. Karyotyping can be used to screen forabnormal numbers of chromosomes ordefective chromosomes associated withcertain congenital disorders, such as Down syndrome.
TECHNIQUE Karyotypes are prepared fromisolated somatic cells, which are treated witha drug to stimulate mitosis and then grown inculture for several days. A slide of cells arrested in metaphase is stained and then viewedwith a microscope equipped with a digital camera.A digital photograph of the chromosomes is enteredinto a computer, and the chromosomes are electronically rearranged into pairs according to size and shape.
RESULTS This karyotype shows the chromosomes from a normal human male. The patterns of stainedbands help identify specific chromosomes and partsof chromosomes. Although difficult to discern in the karyotype, each metaphase chromosome consists oftwo, closely attached sister chromatids (see diagram).
5 µmPair of homologouschromosomes
Centromere
Sisterchromatids
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Figure 13.4 Describing chromosomes
Key
Maternal set ofchromosomes (n = 3)
Paternal set ofchromosomes (n = 3)
2n = 6
Two sister chromatidsof one replicatedchromosome
Two nonsisterchromatids ina homologous pair
Pair of homologouschromosomes(one from each set)
Centromere
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Figure 13.5 The human life cycleKey
Haploid (n)
Diploid (2n)
Haploid gametes (n = 23)
Ovum (n)
SpermCell (n)
MEIOSIS FERTILIZATION
Ovary Testis Diploidzygote(2n = 46)
Mitosis anddevelopment
Multicellular diploidadults (2n = 46)
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Diploidmulticellular
organism
Key
MEIOSIS FERTILIZATION
MEIOSIS FERTILIZATION
MEIOSIS FERTILIZATION
n
n
n
n n
n
n n
n
n
n
n
n
2n2n
2n2n2n
Zygote
GametesHaploid multicellular
organism (gametophyte)Haploid multicellular
organism
Haploid
Diploid
Mitosis Mitosis
SporesGametes
Mitosis Mitosis
Gametes
Mitosis
Zygote
ZygoteMitosis
(a) Animals
Diploidmulticellularorganism(sporophyte)
(b) Plants and some algae (c) Most fungi and some protists
Figure 13.6 Three types of sexual life cycles
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Figure 13.7 Overview of meiosis: how meiosis reduces chromosome number
Interphase
Homologous pairof chromosomesin diploid parent cell
Chromosomesreplicate
Homologous pair of replicated chromosomes
Sisterchromatids Diploid cell with
replicatedchromosomes
1
2
Homologous chromosomes separate
Haploid cells withreplicated chromosomes
Sister chromatids separate
Haploid cells with unreplicated chromosomes
Meiosis I
Meiosis II
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 13.8 The Meiotic Division of an Animal Cell
Centrosomes(with centriole pairs)
Sisterchromatids
Chiasmata
Spindle
Tetrad
Nuclearenvelope
Chromatin
Centromere(with kinetochore)
Microtubuleattached tokinetochore
Tetrads line up
Metaphaseplate
Homologouschromosomesseparate
Sister chromatidsremain attached
Pairs of homologouschromosomes split up
Chromosomes duplicate Homologous chromosomes(red and blue) pair and exchangesegments; 2n = 6 in this example
INTERPHASE MEIOSIS I: Separates homologous chromosomes
PROPHASE I METAPHASE I ANAPHASE I
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Figure 13.8 The Meiotic Division of an Animal Cell
TELOPHASE I ANDCYTOKINESIS
PROPHASE II METAPHASE II ANAPHASE II TELOPHASE II ANDCYTOKINESIS
MEIOSIS II: Separates sister chromatids
Cleavagefurrow Sister chromatids
separate
Haploid daughter cellsforming
During another round of cell division, the sister chromatids finally separate;four haploid daughter cells result, containing single chromosomes
Two haploid cellsform; chromosomesare still double
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Figure 13.9 A comparison of mitosis and meiosis
MITOSIS MEIOSIS
Prophase
Duplicated chromosome(two sister chromatids)
Chromosomereplication
Chromosomereplication
Parent cell(before chromosome replication)
Chiasma (site ofcrossing over)
MEIOSIS I
Prophase I
Tetrad formed bysynapsis of homologouschromosomes
Metaphase
Chromosomespositioned at themetaphase plate
Tetradspositioned at themetaphase plate
Metaphase I
Anaphase ITelophase I
Haploidn = 3
MEIOSIS II
Daughtercells of
meiosis I
Homologuesseparateduringanaphase I;sisterchromatidsremain together
Daughter cells of meiosis II
n n n n
Sister chromatids separate during anaphase II
AnaphaseTelophase
Sister chromatidsseparate duringanaphase
2n 2nDaughter cells
of mitosis
2n = 6
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Figure 13.10 The independent assortment of homologous chromosomes in meiosis
Key
Maternal set ofchromosomes
Paternal set ofchromosomes
Possibility 1
Two equally probable arrangements ofchromosomes at
metaphase I
Possibility 2
Metaphase II
Daughtercells
Combination 1 Combination 2 Combination 3 Combination 4
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 13.11 The results of crossing over during meiosis
Prophase Iof meiosis
Nonsisterchromatids
Tetrad
Chiasma,site ofcrossingover
Metaphase I
Metaphase II
Daughtercells
Recombinantchromosomes