Meiosis gamete production with turning point

Reduction-DivisionGenetic

Recombination

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The form of cell divisioncell division by which GAMETESGAMETES, , with HALFHALF the number of CHROMOSOMESCHROMOSOMES, , are produced.

DIPLOIDDIPLOID (2n) (2n) HAPLOIDHAPLOID (n) (n) MeiosisMeiosis is SEXUALSEXUAL

reproduction.reproduction. TWOTWO divisions divisions (MEIOSIS IMEIOSIS I and

MEIOSIS IIMEIOSIS II).2

Sex cells divide to produce GAMETESGAMETES (sperm or egg)(sperm or egg).

Gametes have HALFHALF the # of chromosomes.

Occurs only in GONADSGONADS (testes or ovaries).(testes or ovaries).

Male: Male: SPERMATOGENESISSPERMATOGENESIS

Female: Female: OOGENESISOOGENESIS

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2n=46

humansex cell

diploid (2n)

n=23

n=23

Meiosis I

n=23

n=23

n=23

n=23

sperm

haploid (n)

Meiosis II4

2n=46

humansex cell

diploid (2n)

n=23

n=23

Meiosis I

n=23egg

Haploid (1n)

Meiosis II5

Polar Bodies (die)

Similar to mitosismitosis interphase. CHROMOSOMESCHROMOSOMES replicate in the S S

phase.phase. Each duplicated chromosomechromosome

consist of twotwo identicalidentical sistersister CHROMATIDSCHROMATIDS attached at their CENTROMERESCENTROMERES.

CENTRIOLECENTRIOLE pairs also replicate.

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Nucleus and nucleolus visiblevisible.

nuclear membrane

nucleolus

cell membrane

chromatin

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Cell division Cell division that reduces the chromosome number chromosome number by one-half.one-half.

Four phasesFour phases:a.a. prophase Iprophase Ib.b. metaphase Imetaphase Ic.c. anaphase Ianaphase Id.d. telophase Itelophase I

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Prophase IProphase I

LongestLongest and and most complex most complex phase (90%).phase (90%).

ChromosomesChromosomes condense. SynapsisSynapsis occurs: homologous chromosomeshomologous chromosomes come together to form a tetradtetrad.

TetradTetrad is two chromosomes two chromosomes or four chromatids four chromatids (sister and non-sister chromatids).

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Homologous chromosomes

sister chromatids sister chromatidsTetrad

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Pair of chromosomeschromosomes (maternalmaternal and paternalpaternal) that are similar in shape similar in shape and sizeand size..

Homologous pairs ((tetradstetrads) carry ) carry genes controlling the same inherited genes controlling the same inherited traitstraits.

Each locuslocus (position of a gene) (position of a gene) is in the same position on homologues.

HumansHumans have 23 pairs 23 pairs of homologous homologous chromosomes:chromosomes:a. 22 pairs 22 pairs of autosomesautosomes

b. 1 pair of sex chromsex chromosomesosomes12

LOCLOCII

Paternal Maternal

eye color locus

eye color locus

hair color locus

hair color locus

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Crossing over Crossing over may occur between non-sister chromatidschromatids at sites called chiasmatachiasmata.

Crossing overCrossing over: segments of nonsister chromatidschromatids break and reattach to the other chromatidchromatid.

Chiasmata (chiasma) Chiasmata (chiasma) are where chromosomes touch each other and exchange genes exchange genes (crossing overcrossing over.)

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nonsister chromatids

chiasmata: site of crossing over

variation

Tetrad

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XX chromosome - female XY chromosome - male

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Homologs Homologs separateseparate

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Meiosis Meiosis II

• Nucleus & Nucleolus Nucleus & Nucleolus disappear

• SpindleSpindle forms

• Chromosomes coilcoil & SynapsisSynapsis (pairing) occurs

• TetradsTetrads form & Crossing over Crossing over Occurs

centriolesspindle fiber

asterfibers

19TETRADTETRAD

Shortest phase Tetrads align on the

metaphase plate (equator).

Independent assortment occurs – chromosomes separate randomly

Formula: 2n

Example:Example: 2n = 42n = 4 then then 1n = 2 1n = 2

thusthus 222 2 = 4 = 4 combinationscombinations

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Gametes

metaphase plate

OR

metaphase plate21

In terms of In terms of Independent Independent AssortmentAssortment -how many -how many different combinations of different combinations of sperm could a sperm could a humanhuman malemale produce? produce?

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Formula: 2Formula: 2nn

Human chromosomes:Human chromosomes:2n = 462n = 46

n = 23n = 23 222323 = ~8 million = ~8 million combinationscombinations

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Homologous chromosomes Homologous chromosomes separate and move towards the poles.

Sister chromatids Sister chromatids remain attached at their centromerescentromeres.

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HomologsHomologs separate separate

Each pole now has haploidhaploid (1n) set of chromosomeschromosomes.

CytokinesisCytokinesis occurs and two haploid daughter cells are formed.

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cytokinesis

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Autoso

mes

Gonads

Nucle

i

Ovarie

s

17%

4%0%

78%1. Autosomes2. Gonads3. Nuclei4. Ovaries

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30 31 32 33

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1 gamete

2 gametes

3 gametes

4 gametes

2 new cells

14%9%

14%

64%

0%

1. 1 gamete2. 2 gametes3. 3 gametes4. 4 gametes5. 2 new cells

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30 31 32 33 34

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Mito

sis

Sperm

atoge

nesi...

Oogenesis

Binary fissi

on

0% 4%

88%

8%

1. Mitosis2. Spermatogenesi

s3. Oogenesis4. Binary fission

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30 31 32 33 34

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10 23 46 50

0% 0%

58%

42%

1. 102. 233. 464. 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30 31 32 33 34

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10 23 46 50

0% 0%0%

100%1. 102. 233. 464. 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30 31 32 33 34

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Sperm

Prokaryo

tes

Chromoso

mes

Polar bodies

4%

96%

0%0%

1. Sperm2. Prokaryotes3. Chromosomes4. Polar bodies

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30 31 32 33 34

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Chromoso

mes

Chromatids

Centromeres

Kinetoch

ores

9%5%

27%

59%

1. Chromosomes2. Chromatids3. Centromeres4. Kinetochores

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30 31 32 33 34

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Chromoso

me num...

Chromoso

me num...

4 new cells

Prepara

tions f...

57%

17%13%13%

1. Chromosome number halved

2. Chromosome number doubled

3. 4 new cells4. Preparations for

meiosis II

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30 31 32 33 34

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4%

83%

4%8%

1. Synapsis2. Chiasma3. Haploidism4. Crossing over

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30 31 32 33 34

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Prophas

e I

Metaphase

I

Anaphase I

Telophase I

8%

20%

64%

8%

1. Prophase I2. Metaphase I3. Anaphase I4. Telophase I

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30 31 32 33 34

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Prophas

e I

Metaphase

I

Anaphase I

Telophase I

76%

12%4%8%


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30 31 32 33 34

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Prophas

e I

Metaphase

I

Anaphase I

Telophase I

4%

48%

4%

43%1. Prophase I2. Metaphase I3. Anaphase I4. Telophase I

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30 31 32 33 34

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Prophas

e I

Metaphase

I

Anaphase I

Telophase I

5%0%

27%

68%


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30 31 32 33 34

Sister Sister Chromatids Chromatids SeparateSeparate

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Meiosis IIMeiosis II

No Interphase II No Interphase II or very or very shortshort

No DNA ReplicationNo DNA Replication Remember: Meiosis II is Remember: Meiosis II is

similar to mitosissimilar to mitosis

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Same as Same as ProphaseProphase in in mitosismitosis

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Same as Metaphase in mitosis

metaphase platemetaphase plate44

Same as AnaphaseAnaphase in mitosismitosis

SISTER CHROMATIDS SISTER CHROMATIDS separateseparate

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Same as Same as TelophaseTelophase in mitosis. in mitosis. Nuclei and Nucleoli Nuclei and Nucleoli reform.reform. CYTOKINESISCYTOKINESIS occurs. occurs. Remember: Remember: FOUR HAPLOID FOUR HAPLOID

DAUGHTER cells DAUGHTER cells are produced.are produced.

Called Called GAMETESGAMETES (eggs and sperm) (eggs and sperm)

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1n Sperm cell fertilizes 1n

egg to form 2n zygote

2n=4

sex cell

diploid (2n)

n=2

n=2

meiosis I

n=2

n=2

n=2

n=2

sperm

haploid (n)

meiosis II48

Also known as Also known as GENETIC GENETIC RECOMBINATIONRECOMBINATION

Important to population as the raw Important to population as the raw material for material for NATURAL SELECTION.NATURAL SELECTION.

All organisms are All organisms are NOTNOT alike alike StrongestStrongest “ “most fit” most fit” survive to survive to

reproduce & pass on traitsreproduce & pass on traits

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What are the What are the 33 sources of sources of genetic recombination genetic recombination or or variation? variation?

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1.1. CROSSING OVER CROSSING OVER (prophase (prophase I)I)

2.2. INDEPENDENT ASSORTMENT INDEPENDENT ASSORTMENT (metaphase I)(metaphase I)

3.3. RANDOM FERTILIZATIONRANDOM FERTILIZATION

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A cell containing 20 20 chromosomeschromosomes (diploid)(diploid) at the beginning of meiosis would, at its completion, produce cells containing how many chromosomeschromosomes?

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1010 chromosomes (haploid chromosomes (haploid or 1n)or 1n)

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AAn organized organized picture picture of the chromosomes of a human arranged in pairs arranged in pairs by size by size from largest to smallest.

PPairs 1-221-22 called AUTOSOMESAUTOSOMES

LLast pair are SEX SEX CHROMOSOMESCHROMOSOMES

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Male - XYMale - XY

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Female - XXFemale - XX

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Female - XXFemale - XXDown Syndrome – Trisomy 21

The fusion of a spermsperm and eggegg to form a zygotezygote.

A zygote is a FERTILIZED EGGFERTILIZED EGG

n=23egg

sperm n=23

2n=46zygote

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A cell containing 40 40 chromatidschromatids at the beginning of meiosis would, at its completion, produce cells containing how many chromosomeschromosomes?

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10 chromosomes10 chromosomes

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Chromoso

mes

Prophas

e

DNA Replic

atio...

Chromatids

25% 25%25%25%1. Chromosomes2. Prophase3. DNA Replication4. Chromatids

201 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30

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Prophas

e II

Metaphase

II

Anaphase II

Telophase II

25% 25%25%25%

201 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30

1. Prophase II2. Metaphase II3. Anaphase II4. Telophase II

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Prophas

e II

Metaphase

II

Anaphase II

Telophase II

25% 25%25%25%

201 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30


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Prophas

e II

Metaphase

II

Anaphase II

Telophase II

25% 25%25%25%

201 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30


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Prophas

e II

Metaphase

II

Anaphase II

Telophase II

25% 25%25%25%

201 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30


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Natu

ral s

elect...

Muta

tions

Homogeneous p

o...

Isolation

25% 25%25%25%1. Natural

selection2. Mutations3. Homogeneous

populations4. Isolation

201 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30

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1 2 3 4 5

20% 20% 20%20%20%

1. 12. 23. 34. 45. 5

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30 20

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25% 25%25%25%1. 102. 253. 504. 100

201 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30

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Somatic c

ells

Autoso

mes

Epith

elial c

el...

Sick

le cells

25% 25%25%25%

1. Somatic cells2. Autosomes3. Epithelial cells4. Sickle cells

201 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30

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Embryo

Zygo

te

Haploid ce

ll

Muta

tion

25% 25%25%25%1. Embryo2. Zygote3. Haploid cell4. Mutation

201 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30

Meiosis gamete production with turning point

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