chapter8_part2

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How Cells Reproduce

Chapter 8

Part 2


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8.6 Sexual Reproduction and Meiosis

Two modes of reproduction: asexual and sexual

Asexual reproduction Reproductive mode by which offspring arise from

one parent and inherit that parents genes only

Offspring of asexual reproduction are clones

Clone

A genetically identical copy of an organism


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Sexual Reproduction

Offspring of sexual reproduction vary in shared

traits

Sexual reproduction

Reproductive mode by which offspring arise from

two parents and inherit genes from both


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Inheriting Chromosome Pairs

Offspring of most sexual reproducers inherit

pairs of chromosomes, one of each pair from the

mother and the other from the father

Except for a pair of nonidentical sex

chromosomes, the members of a chromosome

pair have the same length, shape, and set ofgenes these are homologous chromosomes


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Chromosome Pairs


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Variation in Traits

Sexual reproduction mixes up alleles from two

parents, resulting in new combinations of alleles(and traits) in offspring

Variations in allele combinations are introduced

during meiosis


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Meiosis Halves the Chromosome Number

Meiosis occurs in immature reproductive cells(germ cells) of sexually reproducing eukaryotes,forming male and female haploid gametes

Gamete

Mature, haploid reproductive cell

Haploid (n)

Having one of each type of chromosomecharacteristic of the species


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Meiosis Halves the Chromosome Number

Meiosis sorts the chromosomes into new nuclei

twice (meiosis I and meiosis II)

Duplicated chromosomes of a diploid nucleus

(2n) are distributed into four haploid nuclei (n)


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Meiosis I and Meiosis II


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each chromosome in the cell pairswith its homologous partner

then the partners separate


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Gamete Formation


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Reproductive organsof a human male

testis(where sperm

originate)


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17/69Fig. 8-9b, p. 144

Reproductive organsof a human female

ovary(where eggs

develop)


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Animation: Reproductive organs
http://localhost/var/www/apps/conversion/tmp/scratch_5/videos_animations/gamete_producing.html


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Animation: Sperm formation
http://localhost/var/www/apps/conversion/tmp/scratch_5/videos_animations/sperm_formation.html


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Animation: Egg formation
http://localhost/var/www/apps/conversion/tmp/scratch_5/videos_animations/egg_formation.html


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8.7 Meiosis

In meiosis, two nuclear divisions halve the

parental chromosome number

Meiosis I Meiosis II

Meiosis shuffles parental combinations of

alleles, introducing variation in offspring

Crossing over in prophase I

Random assortment in metaphase I


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Crossing Over

Crossing over is recombination between

nonsister chromatids of homologous

chromosomes which produces new

combinations of parental alleles

Crossing over

Homologous chromosomes exchangecorresponding segments during prophase I of

meiosis


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Fig. 8-11b, p. 148

crossover


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Animation: Crossing over
http://localhost/var/www/apps/conversion/tmp/scratch_5/videos_animations/crossover.html


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Fig. 8-10b, p. 147

5 Prophase II 6 Metaphase II 7 Anaphase II 8 Telophase II

There is no DNAreplication between thetwo nuclear divisions.


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Fig. 8-10b, p. 147Stepped Art

one pair of homologouschromosomes

plasmamembrane

spindlemicrotubules

nuclear envelopebreaking up

centrosome

There is no DNAreplication between

the two nucleardivisions.


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Animation: Crossover review
http://localhost/var/www/apps/conversion/tmp/scratch_5/videos_animations/crossover_review.html


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Animation: Meiosis I and II
http://localhost/var/www/apps/conversion/tmp/scratch_5/videos_animations/meiosis_I_and_II.html


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Gamete Formation in Animals

Germ cells in the reproductive organs of animals

give rise to sperm or eggs

Sperm

Mature male gamete

Egg

Mature female gamete, or ovum


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8.9 When Control is Lost

The cell cycle has built-in checkpoints that allow

problems to be corrected before the cycle

advances

Checkpoint gene products are gene expression

controls that advance, delay, or block the cell

cycle in response to internal and externalconditions


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Checkpoint Genes

BRCA genes are tumor suppressor geneswhose products normally repair broken DNA


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8.10 Impacts/IssuesRevisited

The HeLa cell line was established more than 50

years ago without Henrietta Lacks knowledge or

consent

Today, consent forms are required to take tissue

samples, and it is illegal to sell ones own organsor tissues

Digging Into Data:


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HeLa Cells Are a Genetic Mess


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Video: ABC News: Genetically modified


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cancer fighters
http://localhost/var/www/apps/conversion/tmp/scratch_5/videos_animations/Cancer_Fighters.html


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Video: ABC News: Blood test for lung


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cancer
http://localhost/var/www/apps/conversion/tmp/scratch_5/videos_animations/Lung_Cancer.html


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