Chapter 5.2 Meiosis

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5.2 Meiosis

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This man and this woman had been marry years ago.Can you imagine the face or appearance of their child?

Do you think their child has exactly same face with their parent?

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Do you thinks they arebrothers?Give reason to your answer.

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The answer isyes

They are brothers

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They are

Sheikh Ahmad Shukor;Sheikh Taufik Shukor;Sheikh Mustapha ShukorSheikh Arwiz Shukor.

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- Do you have exactly sameappearance or face with yourmother or father or sister orbrother (except you are twins) ?

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What happen if all cell in your body

include reproductive cell only undergomitosis?

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5.2 Meiosis

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Objectives:

State necessity of trait inheritance to continuelife

State necessity maintain diploid no. ofchromosomes over generation

State significance of meiosis

Identify type of cell undergo meiosis.

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Necessity of trait inheritance in offspring

All individual in same species havesame chromosomal number.

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If mitosis only the way cell candivide- each gamete will get acomplete set of chromosome

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Predict what happen after the gametes

fertilize if the cell only undergo mitosis

+ =

2n 2n?

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Predict what happen after the gametes

fertilize if the cell only undergo mitosis

+ =

2n=46 2n=46

92 chromosomes

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Anotomys leander

The Aquatic Rat, Ecuador Fish-Eating Rat, orFish-Eating Rat (Anotomys leander) is a speciesof rodent in the Cricetidae family. It is the only

species in the genus Anotomys. It is found only inEcuador.

Its natural habitats are subtropical or tropical

dry lowland grassland and rivers.

It has 92 chromosomes

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http://en.wikipedia.org/wiki/Cricetidaehttp://en.wikipedia.org/wiki/Cricetidae


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http://upload.wikimedia.org/wikipedia/commons/e/ee/Sigmodon_hispidus1.jpg


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So, why meiosis important?

After fertilization of male and female gametes,the offspring will have twice number ofchromosomes

Hence, in order to maintain the same

chromosomal number of the offspring, the cellmust undergo meiosis.

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Please fill this table in your

bioscore book

Organism Chromosomal number

2n n

Cat 38

Monkey 44

Prawn 127Human 23

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Significance of meiosis

Meio means reduce

Meiosis is process of nuclear divisionthat reduces number ofchromosome in new cells to the half

number of chromosome in parentcells

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Each gametes receive onechromosomes from every pair ofhomologous .

So, gametes contain haploid (n)

number of chromosomes

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Similar with mitosis, meiosis is acontinuous process and consist of twoseparate nuclear division

Meiosis I Meiosis II

However, DNA of each chromosomesreplicates once

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Meiosis I

Begin with single diploid (2n) parent

cell

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Meiosis II

End with resulting of four haploid

(n) daughter cell Each daughter cell geneticallydistinct from other and also fromparent

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During sexual reproduction, the fusion of twogametes will restore the complete numberof chromosome and genetic material

Diploid zygote will be form.

The offspring inherit traits from both

parent to ensure continuation of life

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Fertilization of haploid gametes

= =

Will produce diploid zygote

The number of chromosome will maintain fornext generation

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Where does meiosis occur?

Gametes are sex cells (sperm, eggs)

Arise from germ cells

testes

ovariesanther

ovary

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Where does meiosis occur

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Spermatogenesis

2n=46

humansex cell

diploid (2n)

n=23

n=23

meiosis I

n=23

n=23

n=23

n=23

sperm

haploid (n)

meiosis II

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Answer this question without referring book

1. State significance of meiosis

2.How many nuclear division do meiosis have? State thedivision.

3.How many daughter cell will produced by meiosis?

4. Describe the genetic content of the daughter cells

5. Where does meiosis occur (in plant and animal)?What type of cell produce in animal and in plant (state

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Concept correction

Some organism can have same number ofchromosome , however their arrangement ofchromosomes are different

Example: Canis familiaris (domestic dog) 78

Gallus gallus (chicken) 78

Rhesus Monkey 48Orangutan 48

Deer Mouse 48

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Chromosome

How to count chromosome

This I single

chromosomeor chromatid

The number ofchromosomecan count by

the number ofthe centromere

Sisterchromatid

centromere

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overview

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Interphase I

Similar to mitosis interphase.

Chromosomes replicate (S phase).

Each duplicated chromosome consist oftwo identical sister chromatids attachedat their centromeres.

Centriole pairs also replicate.

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Interphase I

Nucleus and nucleolus visible.

nuclearmembrane

nucleolus

cell membrane

chromatin

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MEIOSIS I (4 PHASE )

-PROPHASE I

-METAPHASE I-ANAPHASE I

-TELOPHASE I

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Prophase I

Chromosome condense, shorter, thickerand clearly visible

Homologous chromosomes come togetherform bivalent through synapsis

The bivalent visible as four-partstructure known as tetrad

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Tetrad- consist of two homologouschromosome. Each made up of 2sister chromatids

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Prophase I - Synapsis

Homologous chromosomes

sisterchromatids sister chromatidsTetrad6/26/2012 Azuwin 2010


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Homologous Chromosomes

Pair of chromosomes (maternal and paternal) thatare similar in shape and size.

Homologous pairs (tetrads) carry genes controlling

the same inherited traits. Each locus(position of a gene) is in the same

position on homologues.

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Paternal Maternal

eye colorlocus

eye colorlocus

hair colorlocus

hair colorlocus

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CONTINUEProphase I

Non sister chromatids exchangesegments of DNA in crossing over process

Crossing over resulted new combination ofgene on chromosome.

Chiasmata (chiasma) are the sites ofcrossing over in which the segment ofchromatid change

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Crossing Over - variation

nonsister chromatids

chiasmata: siteof crossing overvariation

Tetrad

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Prophase I

centriolesspindle fiber

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At the end-nucleolus and nuclearmembrane disappear

Centrioles migrate to opposite poles

Spindle fiber radiate

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Metaphase I

Tetrad line up at metaphase plate.

One chromosome of each pair attach to spindlefiber from one pole and its homologoue attachby opposite pole fiber

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Metaphase I

metaphase plate

OR

metaphase plate

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Anaphase I

Spindle fiber pull the homologous chromosomesto separate the homologous chromosome s movetowards opposite poles.

Sister chromatids remain attached at theircentromeres.

So, although the cell started with 4

chromosomes , only 2 chromosomes movetowards each pole

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T l h I


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Telophase I

Chromosomes arrive at poles.

Each pole now has haploid set of chromosomes in the nucleus

Spindle fiber disappear

Nuclear membrane reappear. Nucleolus reappear in eachnucleus.

Cytokinesis occurs and two haploid daughter cells areformed.

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Cytokinesis occur simulteneously aftertelophase I

Why we need meiosis II?

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MEIOSIS II (4 PHASE )

-PROPHASE II

-METAPHASE II-ANAPHASE II

-TELOPHASE II

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same as prophase in mitosis

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Nuclear membrane disintergrate

Spindle fiber reform

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metaphase platemetaphase plate

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Chromosome-still consist of sisterchromatids

Position randomly at metaphaseplate with sister chromatids ofeach chromosome pointing towaardopposite pole

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sister chromatids separate

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Centromere of sister chromatidsseparate

The sister chromatid now isindividual chromosomes

Chromosomes move toward oppositepoles

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Nuclear envelope reappear

Nucleoli reform.

Cytokinesis occurs.

Remember: four haploid daughter cells

produced.

gametes = sperm or egg

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Animation

M i i t t


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Meiosismouse testes

Parent cell

4 gametes

1st division

2nd division

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Differences of meiosis I and IIMeiosis I Differences Meiosis II

-Homologous chromosome pairsup- crossing over between nonsister chromatid

PROPHASE -no synapsis of homologouschromosome- No crossing over

-Homologous chromosomes alignat equator

METAPHASE -chromosomes align at equator

-Homologous chromosomeseparate and move to oppositepoles- siser chromatid attach atcentromere

ANAPHASE -sister chromatid separatebecoming daughterchromosome

-Produce 2 haploid daughter cell-each daughter cell has only oneof each type of chromosome

TELOPHASE -4 haploid daughter cellproduced-each cell have only one of thesister chromatid-Have same number ofchromosome with haploid cellfrom meiosis I

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Breaktime

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Differences of mitosis and meiosis

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M i i k diff f i i


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Meiosiskey differences from mitosis

Meiosis reduces the number of chromosomes byhalf.

Daughter cellsdiffer from parent, and eachother.

Meiosis involves two divisions, Mitosis only one.

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Mitosis vs meiosis


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Mitosis vs. meiosis

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Meiosis creates genetic variation

During normal cell growth,mitosis

producesdaughter cells identical to parent cell (2n to 2n)

Meiosis results in genetic variation by shufflingof maternal and paternal chromosomes and

crossing over.

No daughter cells formed during meiosis aregenetically identical to either mother or father

During sexual reproduction, fusion of the uniquehaploid gametes produces truly unique offspring.

Study Questions


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Study Questions1.What happens as homologous chromosomes

pair up during prophase I of meiosis?

2. How does metaphase of mitosis differ frommetaphase I of meiosis?

3. What is the sole purpose of meiosis?

4. What specific activities, involving DNA, occurduring interphase prior to both mitosis andmeiosis?

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5. Compare mitosis and meiosis on the

following points:a. number of daughter cells produced.b. the amount of DNA in the daughter cells incontrast to the original cell.

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5.3 Appreciating the

movement ofchromosomes during

mitosis and meiosis

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Meiosis di ision e o


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Meiosisdivision error

Chromosome pair6/26/2012 Azuwin 2010

Meiosis error fertilisation


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Meiosis error - fertilisation

Should the gamete with thechromosome pair befertilised then the offspringwill not be normal.

In humans this often occurswith the 21st pair producinga child with Downs Syndrome

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21 trisomyDowns Syndrome

Can you see

the extra21stchromosome?

Is this

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Monosomy


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Monosomy

refers to lack of one chromosome of thenormal complement.

Monosomy of the sex chromosomes (45,X)

causes Turner syndrome.

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trisomy


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trisomy

Trisomy 18 known as EdwardsSyndrome

Trisomy 13 known as PatauSyndrome

Trisomy of the sex chromosomes ispossible, such as in (47,XXX).

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http://en.wikipedia.org/wiki/Trisomy_18http://en.wikipedia.org/wiki/Trisomy_18http://en.wikipedia.org/wiki/Trisomy_18http://en.wikipedia.org/wiki/Trisomy_18


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The end


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The end

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HOW VARIATION OCCUR IN MEIOSIS

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Independent assortment


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Independent assortment

Number of combinations: 2n

e.g. 2 chromosomes in haploid2n = 4; n = 22n = 22 = 4 possible combinations

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In humans


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In humans

e.g. 23 chromosomes in haploid2n = 46; n = 232n = 223 = ~ 8 million possible combinations!

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Crossing over


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Crossing overChiasmata sites of crossing over, occurin synapsis. Exchange of genetic

material between non-sister chromatids.

Crossing over produces recombinantchromosomes.

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H l i h


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Harlequin chromosomes

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Random fertilization


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Random fertilizationAt least 8 million combinations from

Mom, and another 8 million from Dad

>64 trillion combinations for a diploid

zygote!!!

Chapter 5.2 Meiosis

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