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COMPARING MITOSIS AND MEIOSIS

© 2007 Paul Billiet ODWS

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COMPARING MITOSIS AND MEIOSIS

© 2007 Paul Billiet ODWS

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Control of mitosis:CYCLIN

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Eukaryotic cells??• The nucleus?• Nuclear membrane• Chromosomes…not

chromosome…?• All that ‘stuff’ in the

cytoplasm?

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Kinetochore (centromere)

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Chromosomes duplicate

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Eukaryotic cell cycle• Cell is ‘born’• Duplicates DNA??• Grows to…size?• Prepares to divide• Divides=mitosis

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Mitosis produces identical offspring (2N---2N)

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Importance???• Growth• Replacement• Cancer• Regeneration of…

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Name stage of mitosis

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Name stage of mitosis

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Name stage of mitosis

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Name stage of mitosis

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Name stage of mitosis

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Name stage of mitosis

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Name stage of mitosis

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Name stage of mitosis

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Meiosis – A Source of Meiosis – A Source of DistinctionDistinction

Why do you share some but not all characters of each parent?

What are the rules of this sharing game?

At one level, the answers lie in meiosis.

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Why do we need meiosis?Why do we need meiosis?

• Meiosis is necessary to halve the Meiosis is necessary to halve the number of chromosomes going into number of chromosomes going into the sex cellsthe sex cells

Why halve the chromosomes in Why halve the chromosomes in gametes?gametes?

• At fertilization the male and female sex At fertilization the male and female sex cells will provide cells will provide ½ of the ½ of the chromosomeschromosomes each – so the offspring each – so the offspring has genes from both parentshas genes from both parents

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2) Meiosis 2) Meiosis scramblesscrambles the specific forms of the specific forms of each gene that each sex cell (egg or sperm) each gene that each sex cell (egg or sperm) receives. receives.

This makes for a lot of This makes for a lot of genetic diversitygenetic diversity. This . This trick is accomplished through trick is accomplished through independent independent assortmentassortment and and crossing-overcrossing-over..

Genetic diversity is important for the Genetic diversity is important for the evolution evolution of populations and speciesof populations and species..

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MeiosisMeiosis

Parent cell – chromosome pair

Chromosomes copied

1st division - pairs split

2nd division – produces 4 gamete cells with ½ the original no. of chromosomes

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Meiosis – mouse testes Meiosis – mouse testes Parent cell

4 gametes

1st division

2nd division

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The Stages of Meiosis:

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Figure 13.7 The stages of meiotic cell division: Meiosis I

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Meiosis II : Meiosis II : Separates sister Separates sister

chromatidschromatids

• Proceeds similar to mitosisProceeds similar to mitosis

• THERE IS NO INTERPHASE II !THERE IS NO INTERPHASE II !

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Figure 13.7 The stages of meiotic cell division: Meiosis II

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The Key Difference Between Mitosis and Meiosis is The Key Difference Between Mitosis and Meiosis is the Way Chromosomes Uniquely Pair and Align in the Way Chromosomes Uniquely Pair and Align in

Meiosis Meiosis

MitosisMitosis The first (and The first (and distinguishing) distinguishing) division of meiosisdivision of meiosis

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Meiosis I, Prophase I

• Leptotene – chromosomes become apparent

• Zygotene– homologous chromosomes pair synapsis form tetrad

• Pachytene– crossing over occurs

• Diplotene– chromosomes start to separate but held together by

chiasmata• Diakinesis

– Further shortening of homologous chromosomes

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Oogonium

Primaryoocyte

Secondaryoocyte

Polar Body I

Fertilized Ovum

Polar Body II

Gametogenesis

Spermatogonium

Primaryspermatocyte

Secondaryspermatocytes

4 spermatids

4 spermatozoa

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Oogonium

Primaryoocyte

Secondaryoocyte

Polar Body I

Fertilized Ovum

Polar Body II

Males

Spermatogonium

Primaryspermatocyte

Secondaryspermatocytes

4 Spermatids

4 spermatozoa

Mitosis

Throughout Life

At Puberty

MeiosisComplete in

64days

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MitosisFetal period

Before or at birth

After birth

After puberty

At fertilization

Meiosis in progress

Arrested indiplotene

of Meiosis I

Meiosis Icomplete

Arrest atMetaphase II

Meiosis IIcomplete

Oogonium

Primary Oocyte

Secondary Oocyte& Polar Body I

Fertilized Ovum& Polar body II

Females

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Differences in Gametogenesis

Male• Puberty• 60-65 days• 30-500 mitoses• 4 spermatids• 100-200

million /ejaculate

Female• Early embryonic development• 10-50 years• 20-30• 1 ovum and polar bodies• 1 ovum / menstrual cycle

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Female human embryoStages in gonad

• 2 months gestation – oogonia start meiosis

• 5 months arrest in meiosis I (diplotene/dictyotene)

• 6 months chromosomes held together by chiasmata

• By puberty 100,000 remain

• Maximum 300-400 mature

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Meiosis – division errorMeiosis – division error

Chromosome pair

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Meiosis error - Meiosis error - fertilizationfertilization

Should the gamete with the Should the gamete with the chromosome pair be fertilized chromosome pair be fertilized then the offspring will not be then the offspring will not be ‘normal’.‘normal’.

In humans this often occurs In humans this often occurs with the 21with the 21stst pair – producing pair – producing a child with Downs Syndromea child with Downs Syndrome

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21 trisomy – Downs 21 trisomy – Downs SyndromeSyndrome

Can you see the extra 21st chromosome?

Is this person male or female?

• و -15 پروكاريوتيكها ژنتيكي اختالالت و تشابهاتبوتيكها بوكار

• كروموزومها و ژنها با رابطه در حياتي سيكل

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