Meiose

Professora RaquelCED 416 – Santa Maria

Maio 2015

MeioseUma célula diploide forma célula haploide

Meiose: Divisão em duas partes

Homólogos se separam

Cromátides-irmãsse separam

haploide

Meiose I

MeioseII

Diploide

Haploide

Divisão reducionalDivisão equacional

4 cromossomos

2 cromossomos 2 cromossomos

Meiose animal forma GametesMeiose tem tem que reduzir o número de

cromossomos pela metadeA fertilização restaura o número 2n

da mãe Do pai criança

demais!

O número certo!

Interfase

Meiose: prófase I

Fim

Meiose I: Divisão reducional

Núcleo Fibras de fuso Envelopenuclear

Profase I(Cromossomo duplicado)

Profase I

Metafase I Anafase I Telofase I (haploide)

Profase I

Início da profasePar de homólogos .Crossing over ocorre.

Fim da profaseCromosomos se condensam.Spindle forms.Envelope nuclear se fragmenta.

Cromossomos duplicados

Homólogos (mesmos genes, diferentes alelos)

Cromátides-irmãs(mesmos genes,mesmos alelos)

Gene X

Homólogos se separam na meiose I e então diferentes alelos se separam.

Tétrades se formam na Profase I

Cromossomos homólogos (cada um com suas cromátides)

Unem-se para formar a TÉTRADE

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Crossing-OverHomologous

chromosomes in a tetrad cross over each other

Pieces of chromosomes or genes are exchanged

Produces Genetic recombination in the offspring

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Homologous Chromosomes During Crossing-Over

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Crossing-over multiplies the already huge number of different gamete types produced by independent assortment

Crossing-Over

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Metaphase I

Homologous pairs of chromosomes align along the equator of the cell

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Anaphase I

Homologs separate and move to opposite poles.

Sister chromatids remain attached at their centromeres.

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Telophase I

Nuclear envelopes reassemble.

Spindle disappears.

Cytokinesis divides cell into two.

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Meiosis II

Only one homolog of each chromosome is present in the cell.

Meiosis II produces gametes with one copy of each chromosome and thus one copy of each gene.

Sister chromatids carry identical genetic information.

Gene X

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Meiosis II: Reducing Chromosome Number

Prophase IIMetaphase II

Anaphase IITelophase II

4 Genetically Different haploid cells

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Prophase II

Nuclear envelope fragments.

Spindle forms.

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Metaphase II

Chromosomes align along equator of cell.

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Anaphase II

Sister chromatids separate and move to opposite poles.

Equator

Pole

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Telophase IINuclear envelope assembles.

Chromosomes decondense.

Spindle disappears.

Cytokinesis divides cell into two.

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Results of MeiosisGametes (egg & sperm) form

Four haploid cells with one copy of each chromosome

One allele of each gene

Different combinations of alleles for different genes along the chromosome

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Meiosis Animation

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