Regents Biology 2006-2007

Meiosis &Sexual Reproduction

Regents Biology

Cell division / Asexual reproduction Mitosis

produce cells with same information identical daughter cells

exact copies clones

same number of chromosomes same genetic information

Aaaargh!I’m seeing

double!

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Cell Division in Prokaryotes Binary fission is the process of cell

division in prokaryotes.

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Asexual reproduction Single-celled eukaryotes

yeast Paramecium Amoeba

Simple multicellular eukaryotes Hydra

budding

What are thedisadvantages of

asexual reproduction?

What are the advantages?

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How about the rest of us? What if a complex multicellular organism

(like us) wants to reproduce? joining of egg + sperm

Do we make egg & sperm by mitosis?

46 46+ 92

egg sperm zygote

What if we did, then….

Doesn’t work!

No!

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Human female karyotype

46 chromosomes23 pairs

XX

diploid = 2 copies 2n

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46 chromosomes23 pairs

XY

Human male karyotypediploid = 2 copies 2n

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How do we make sperm & eggs? Must reduce 46 chromosomes 23

must half the number of chromosomes haploid

23

2346

egg

sperm

46

meiosis 46

fertilization

23

23

zygote

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Formation of Haploid Cells Meiosis is a process of nuclear

division that reduces the number of chromosomes in new cells to half the number in the original cell.

Meiosis leads to four haploid cells (gametes) rather than two diploid cells as in mitosis.

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Meiosis makes sperm & eggs 46 chromosomes to 23 chromosomes

half the number of chromosomes

23

2346

egg

sperm

46

meiosis

haploiddiploid

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Paired chromosomes Homologous chromosomes

both chromosomes of a pair carry “matching” genes control same inherited characters homologous = same information

diploid2n

2n = 4

homologouschromosomes

double strandedhomologous chromosomes

eye color(brown?)

eye color(blue?)

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Meiosis I Meiosis I includes prophase I,

metaphase I, anaphase I, and telophase I.

Crossing-over, which is when portions of homologous chromosomes exchange genetics material, occurs during prophase I and results in genetic recombination.

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Meiosis II Meiosis II includes prophase II,

metaphase II, anaphase II, and telophase II.

Four new haploid cells result.

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Meiosis 1 overview 1st division of meiosis

4 chromosomes diploid 2n 2 chromosomes

haploid 1n

doublestrande

d

Copy DNA

Line Up 1

Divide 1

gamete

prophase 1

metaphase 1

telophase 1

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2nd division of meiosis looks like mitosis

Meiosis 2 overview

2 chromosomes haploid 1n

4

gametes

Line Up 2

Bye Bye 2

telophase 1

metaphase 2

telophase 2

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Meiosis

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Meiosis = reduction division Meiosis

special cell division in sexually reproducing organisms

reduce number of chromosomes 2n 1n diploid haploid

half

makes gametes sperm, eggs

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Meiosis & mitosis

Meiosis to make gametes sperm & egg

Mitosis to make copies of cells growth repair development

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Development of Gametes Spermatogenesis is the process by

which sperm cells are produced.

Oogenesis is the process that produces mature egg cells.

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Meiosis in Male & Female Animals

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Sexual Reproduction Sexual reproduction is the formation

of offspring through meiosis and the union of a sperm and an egg.

Offspring produced by sexual reproduction are genetically different from the parents.

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Sexual reproduction lifecycle

1 copy haploid 1n

2 copies diploid 2n

1 copy haploid 1n

meiosis

fertilization

We’re mixingthings up here!A good thing?

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mitosis

zygote

Putting it all together…

23

2346

egg

sperm

46

meiosis 4623

23

fertilization mitosis &development

meiosis fertilization mitosis + development

46

46

46

46

46

4646 46

gametes

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The value of meiosis 1 Consistency over time

meiosis keeps chromosome number same from generation to generation

from Mom

from Dad

offspring

Dad

Mom

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The value of meiosis 2 Change over time

meiosis introduces genetic variation gametes of offspring do not have

same genes as gametes from parents new combinations of traits

from Mom

from Dad

new gametes made by offspring

offspring

We’remixing things

up here!

variation

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How does this explain:family resemblance & differences!Why are the kids so similar to

the parents but not exact?

Martin & Charlie Sheen, Emilio Estevez

Michael & KirkDouglas

Baldwin brothers

Regents Biology 2006-2007

Any Questions??

What are theDISadvantages of

asexual reproduction?

What are theDISadvantages of

sexual reproduction?

What are theadvantages of

sexual reproduction?

What are theadvantages of

asexual reproduction?