Meiosis

Cell DivisionCell Division

Mitosis Meiosis

The stages of mitotic cell division in an animal cell:G2 phase; prophase; prometaphase

.The stages of mitotic cell division in an animal cell:metaphase; anaphase; telophase and cytokinesis

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1. mother cell give 2 daughter cells2. Each daughter cell have :

: The same number of chromosome equal to mother cell: Set of chromosome equal to mother cell: Genetic material as the same as mother cell

2n = 41 chromosome

has 1 chromatid

Mother cell2n = 4

2 Daughter cell

Mitosis is complete : Two new cells are formed.

1 chromosome has 2 chromatid

1 chromosomehas

1 chromatid

2n = 4

OBJECTIVES

. 1. Describe events associated with meiosis 2. Distinguish the phases of meiosis on permanent slides

Plants : slides Lilium anther and Lilium ovaryAnimal : Grasshopper's testis, Crayfish's testis

and frog's testis4. Stain and examine chromosomes squashes in Chinese

chive's flower

MeiosisMeiosis

Reduction

2n = 4 n = 2(Haploid)( Diploid)

1. Reduction of number chromosome2. Reduction of set chromosome

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KeyHaploid (n)Diploid (2n)

Haploid gametes (n = 23)

Egg (n = 23 )

Sperm (n = 23 )

MEIOSIS FERTILIZATION

Ovary TestisDiploid zygote

(2n = 46)

Multicellular diploid adults (2n = 46)

Location for meiosis division

For Plant; Male : occur in cone or anther Female : occur in cone or ovule

Angiosperm

Female conesMale cones

Gymnosperm


For Animal; Male : occur in testis Female : occur in ovary

FrogMale Female


For Human; Male : occur in testis Female : occur in ovary

HumanMale Female

Meiosis involves two divisions

Meiosis I : is a reductional division: produces two haploid cells

Diploid cell

Haploid cell

Meiosis II : is a mitotis-like: produces two haploid cells

Meiosis (Meiotic cell division)

Meiosis II

Prophase IIMetaphase IIAnaphase IITelophase II

Meiosis I

Prophase IMetaphase IAnaphase ITelophase I

LeptoteneZygotenePachyteneDiploteneDiakinesis

InterphaseInterphase

Similar to those of mitosis Similar to those of mitosis but occur in sex organbut occur in sex organ

Interphase is composed of : G1 (gap phase 1) – time of cell growth: S phase – synthesis of DNA (DNA replication)

2 sister chromatids are produced: G2 (gap phase 2) – growth and preparation for meiosis

1 chromosome has

1 chromatid

2n = 4 2n = 4

S , G2G1

1 chromosome has

2 chromatids

MeiosisMeiosis

: Genetic material dispersed in the nucleus as long strands of chromatin

: Thin chromatin strands commonly appear as amorphous granular material

: Presence of nuclear membrane and nucleolus

InterphaseInterphase

nucleolus

chromatin

nucleus

Prophase I

Differs from prophase of mitosis

Homologous chromosomes come to lie sideby side in a pairing process called synapsis.

Each pair of synapsed chromosomes is called a bivalent(two chromosomes) or a tetrad (four chromatids)

synapsis.

Mitosis Meiosis

due to

The events of prophase I can be subdivided into five stages

1. Leptotene

2. Zygotene

3. Pachytene

4. Diplotene

5. Diakinesis

1.1 Leptotene or Leptonema (slender ribbon)

• Long, thin chromosomes start to condense • Nucleolus presence

Prophase I

Nucleolus

1.2 Zygotene or Zygonema (paring)

bivalenttetrad

: Chromosomes condense : Homologous chromosomes come to lie side by side in a

pairing process called synapsis: Each pair of synapsed chromosomes is called a bivalent

(two chromosomes) or a tetrad (four chromatids)

2n = 41 chromosome

has 2 chromatids

1.3 Pachytene (thick ribbon)

: Chromosomes more condense : Nonsister chromatids of a tetrad crossover, called this phenomena

crossing over resulting in an exchange of genetic materialcalled genetic recombinant

: The point of exchange appears as a cross-shaped figure called a chiasma

Chiasma

1.4 Diplotene or Diplonema (double)

: The paired of homologous chromosomes separate: The chromosomes themselves uncoil a bit : The homologous chromosomes of each bivalent

remain tightly bound at chiasmata

1.5 Diakinesis (moving apart)

: The final stage of the first prophase of meiosis: The chromosomes reach their maximal condensation

at this stage : The nucleoli and nuclear membrane disappear: The spindle fiber reform

2n = 4

1 chromosome has

2 chromatids

Metaphase I

The bivalents orient at random on the equatorial plane

2n = 4

1 chromosome has

2 chromatids

Mitosis : Metaphase Meiosis I : Metaphase I

2n = 41 chromosome has 2 chromatids

Anaphase I

: The homologous pairs of chromosomes separate and move to opposite poles

: The centromeres do not separate, but continue holdsister chromatids together ,so each chromosomes consists of two sister chromatids

: This stage reduces the chromosome number from the diploid (2n) to the haploid (n) state.

haploid, nMetaphase I

4n = 8 2n = 4

Mitosis: Anaphase Meiosis I : Anaphase I

1 Chromosomehas

1 Chromatids

1 Chromosomehas

2 Chromatids

*** Note ***Mitosis

Metaphase

Anaphase

Metaphase I

Anaphase I

Meiosis ITelophase I

: Chromosomes have reached their polar destinations : Nuclear membrane and nucleolus reforms : Cytokinesis occurs

Anaphase I

After finish Telophase I

1. Mother cell give 2 haploid daughter cells2. Each haploid daughter cell have :

: The number of chromosomes reduced by half of mother cell : Each chromosome has two chromatid ( diad chromosome ): Set of chromosome reduced by half of mother cell: Genetic material may be or may not be uniformly

2n = 4

n = 2

1 chromosomehas 2 chromatids

1 chromosomehas 2 chromatids

2n = 4

2n = 42n = 4

2n = 4

n = 2 n = 2

After Meiosis IAfter Mitosis

1 chromosomehas

1 chromatids

1 chromosomehas

2 chromatids ( Diad chromosome )

Short Interkinesis

After finish Telophase IEach haploid daughter cell

Go into Mitosis II

: Chromosomes may uncoil and return to an interphase-like condition with reformation of a nuclear membrane

: No DNA synthesis occurs during interkinesis.

No short Interkinesis

: Immediately go into

Prophase II

Meiosis II : similar to those of Mitosis

Prophase II

: The chromosomes recondense. : Nuclear membrane and nucleolus disappear: Spindle fiber reform: Each chromosome has 2 chromatids ( Diad chromosome)

n = 2

1 chromosomehas

2 chromatids( Diad chromosome )

Metaphase IIProphase II Metaphase II

n = 21 chromosome

has 2 chromatids

( Diad chromosome )

: Chromosome more condense: The individual chromosomes have lined up

on the equatorial plane

Anaphase IIMetaphase II Anaphase II

: The centromeres of each chromosome separate : Spindle fiber separate sister chromatids to be

pulled apart (now, referred to again as chromosomes)

2n = 41 chromosome

has 1 chromatids

( Monad chromosome

Telophase II

: Chromosomes begin to uncoil: Nuclear membrane and nucleolus reappears in

each new nucleus: Spindle fiber degenerate

Anaphase II Telophase IIAfter finish Telophase II

Begin with each haploid daughter cell

Each haploid daughter cell give two haploid progeny cells

n = 21 chromosome

has 2 chromatids

( Diad chromosome )

n = 21 chromosome

has 1 chromatids

( Monad chromosome )

Telophase IITelophase I

n = 21 chromosome

has 2 chromatids

( Diad chromosome )

n = 21 chromosome

has 1 chromatids

( Monad chromosome )

Compare between Telophase I and Telophase II Conclution : Meiosis

: From 1 diploid mother cell gives four haploid progeny cells: The number of chromosomes reduced by half of mother cell: Set of chromosome reduced by half of mother cell: Genetic material may not be uniformly of either maternal

or paternal origin

41

To produce gamete : egg or sperm

involved

Fertilization

Why meiosis division have to reduce set of chromosomeand number of chromosome

To maintain the same species


Haploid sperm

Diploid zygote

Haploid egg

Diploid dad

Diploid mom

Equal to parent

Equal to parent

2n = 6

n = 3

n = 3

2n = 6

2n = 6

To maintain the same species


46

46 46

92?

Genetic variation

After fertilization

46

47

Possibility 1 Possibility 2

Two equally probablearrangements ofchromosomes at

metaphase I

Metaphase II

Daughtercells

Combination 1 Combination 2 Combination 3 Combination 4

The independent assortment of homologous chromosomesin metaphase I

Mom's posssible gametes(2n)

Dad's posssible gametes(2n)

N = Number of chromosome pairs

22 = 4

Result of Independent assortment

22 = 4

Egg

Sperm

MEIOSIS FERTILIZATION

OvaryTestis

Multicellular diploid adults (2n = 46)

223 = 8,388,608

Human posssible gametes from independent assortment

223 = 8,388,608

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Crossing over in prophase I

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Genetic variation

EXTINCTION!!

Globalwarming

Survival

Globalwarming

Genetic diversity lead to selection

No genetic variation

1. Study meiosis in the anther of Chinese chive's flower by Squash technique

6 stamens, a singleslender style

HCl 10 min

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2

3

4

5

6

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Bring the anther part of Chinese chive's flower on a clean slide. Add a drop of 5% HCland leave for 5-10 min.to causing cell wallto be softed and easily for squashing

Break up the tissue with a dissecting needle

Add a drop of aceto-orcein stain the tissuefor 3-5 min.

Tease the tissue apart with dissecting needles

Cover with a coverslip

Spread the cells out by gently pressing down on the coverslip with your finger or a pencil eraser

Gently pass the slide over a flame , then use microscope focus on low power, and thenswitch to medium or high power to find

meiosis I and meiosis II

Squash technique

2. Distinguish the phases of meiosis in Lilium antheron permanent slides

Plants Slides Lilium anther

3. Distinguish the phases of meiosis in animal testison permanent slides

Grasshopper testis Frog testis Crayfish testis

Plants : Slides Lilium ovary

4. Distinguish the phases of meiosis in Lilium ovaryon permanent slides Result

Finish meiosis I : Diad microspore

Finish meiosis II : Tetrad microspore

1. Study meiosis in the anther of Chinese chive's flower

After finish Meiosis II produce

4 Microspore

Microspore

Study meiosis in the anther of Chinese chive's flower by Squash technique

2.Study meiosis in the Lilium anther on permanent slide

Grasshopper testis Frog testis Crayfish testis

3. Distinguish the phases of meiosis in animal testis on permanent slides

Several lobes of the grasshopper's testis

Grasshopper's testis Early primary spermatocyte Prophase I, substage Pachytene.

Prophase I, substage Diplotene. Prophase I, substage Diakinesis.

Spermatids

Further elongate Mature sperm

heads

tails

Pachytene Diakinesis

Metaphase II

Anaphase IIMetaphase I

Metaphase II

Metaphase I

Telophase I

Telophase I

Spermatid differentiate into sperm ( spermatozoa ) Frog testis

Seminiferous tubule

A

B

Prophase I

Prophase IISperm ( Spermatozoa )

4. Distinguish the phases of meiosis in Lilium ovaryon permanent slides

Megaspore mother cell (2n)

Lilium sp.

2 ( n )

4 nucleate 2(n) + 2(3n)

2 ( 3n )

Meiosis

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