MeiosisThe Continuation of Life

Meiosis: The Continuation of Life

Homologous ChromosomesPaired chromosomes

One from each parent

Genes for same traitAllelesSame order on chromosome

Homologous Chromosomes

Diploid vs. HaploidDiploid Cell that has TWO of each kind of chromosome (parent)2n

Haploid Cell that has ONE of each kind of chromosome1n

QuestionWhat would happen if Mitosis was the only way our cells could divide?

23pairs 46pairs 96pairsetc.

We need a way to divide the Chromosome # in half! What is this called??Meiosis!

MeiosisPurpose make haploid cells

GametesEggSperm

Form Zygote

Phases of MeiosisMeiosis I

Prophase IMetaphase IAnaphase ITelophase I

Meiosis II

Prophase IIMetaphase IIAnaphase IITelophase IICytokinesis

Prophase ISame as in MitosisBut

Homologous Chromosomes find each other

Synapsis Tetrads

Prophase ISynapsis

Crossing over occurs

Exchange of Genetic material

Crossing OverCrossing Over and its products!

Metaphase IHomologous pairs line up

Tetrads still together

Anaphase IHomologous Chromosomes separate

Independent Assortment

Telophase IJust like Telophase in MitosisChromosomes unwindNuclear membrane forms

Meiosis IIJust like Mitosis!!

Meiosis IIProphase IIMetaphase IIAnaphase IITelophase II

Prophase IIChromosomes appearCentrioles migrateSpindle fibers

Metaphase IIChromosomes line upLike mitosis

Anaphase IIChromosomes separate like in mitosisMove to ends of cell

Telophase IINuclear membrane formsChromatids unwind Chromatin

FinallyCytokinesis!

ProductsFrom single diploid (2N) 4 Haploid (1N)

Cellsalive!Meiosis: An Interactive Animation

Web Lesson Meiosis

Mitosis vs. Meiosis

GametesWhy are some of the chromosomes different colors?

Crossing Over!

VariationGenetic Variation is provided by meiosis

Because of assortment 70 trillion possibilities

Crossing Over increases that numberReason for great variety of people

Mistakes in MeiosisNondisjunction the failure of homologous chromosomes to separate properly

Trisomy 1 extra chromosomeMonosomy 1 less chromosomePolyploidy extra set of all chromosomes

TrisomyTrisomy 21Downs Syndrome

Flattened face

Shorter than normal

Heart defects

MonosomyUsually lethal but, but not in

Turners Syndrome

Look at KaryotypeWhat is wrong here?

Turners Syndrome

PolyploidyWhole extra set of chromosomes(3n) or (4n)

Death animal zygotes

Often occurs in plantsBigger and Healthier

Phase? #1

QuestionWhat separates during Meiosis I?

Homologous Chromosomes

QuestionWhat type of cell results from meiosis I?

Haploid!

QuestionWhat separates during Meiosis II?

Sister Chromatids

Questions?

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