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LG: How do we produce gametes? Date: 2/4/13. Attention: from now on, if you see any words or phrases inside this “[ ]” symbol, you need to know them by heart! . [ Mitosis] and [Meiosis]. Mitosis: - division of [ somatic cells] = [ body cells] Meiosis

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Lg how do we produce gametes date 2 4 13

LG: How do we produce gametes? Date: 2/4/13

Attention: from now on, if you see any words or phrases inside this “[ ]” symbol, you need to know them by heart!


Mitosis and meiosis

[Mitosis] and [Meiosis]

  • Mitosis:

    -division of [somatic cells] = [body cells]

  • Meiosis

    -division of [gametes] = [sex cells]


Mitosis meiosis

Mitosis: Meiosis:

Each resulting cell still has chromosomes from mom & dad


Mitosis

Mitosis

Let’s Review!


Asexual reproduction

[Asexual Reproduction]

One parent

Offspring [identical]=(clones)

Quick

No [variation]=difference


I nterphase

[Interphase]

  • Interesting things happen!

  • Cell preparing to [divide]=multiply

  • [Genetic material] doubles (making copies)


Lg how do we produce gametes date 2 4 13

CENTROMERE

GENES

SISTER CHROMATID

SISTER CHROMATID

ONE CHROMOSOME

ONE COPIED CHROMOSOME

Sister Chromatid

– each side of a replicated chromosome


Prophase

[Prophase]

  • [Chromosomes] pair up!

  • Chromosomes thicken and shorten

    -become visible

    -2 chromatids joined by a [centromere]

  • [Centrioles] move to the opposite sides of the nucleus (only in animal cells)

  • [Nuclear membrane] disappears


M etaphase

[Metaphase]

  • Chromosomes meet in the middle!

  • Chromosomes arrange at equator of cell

  • Become attached to [spindle fibres] by centromeres

  • [Homologous chromosomes] do not pair up


What are homologous chromosomes

What are homologous chromosomes?

Definition: chromosomes having the same genes at the same loci (location) but possibly different alleles (alternative forms of a gene). For example, two chromosomes may have genes encoding eye color, but one may code for brown eyes, the other for blue.


A naphase

[Anaphase]

  • Chromosomes get pulled apart

  • Spindle fibres contract pulling chromatids to the opposite poles of the cell


T elophase cytokinesis

[Telophase/Cytokinesis]

  • Now there are two!

  • Nuclear envelope forms around chromosomes

  • Chromosomes uncoil

  • Cytokinesis

    • animals - pinching of plasma membrane

    • plants- elongates and the [cell plate] forms( future cell wall and cell membrane)


What is meiosis for

What is [meiosis] for?

  • Gametes for [Sexual Reproduction]

  • Two parents

  • Offspring all genetically different

  • Takes longer

  • Lots of variations


Meiosis

Meiosis

  • 4 [daughter cells] produced

  • Each daughter cell has half the chromosomes of the parent

  • 2 sets of [cell divisions] involved


Meiosis reduction division

Meiosis = reduction division

  • Meiosis

    • special cell division in sexually reproducing organisms

    • reduce number of chromosomes

      • 2n (46)  1n (23)

      • [diploid]  [haploid]

        • Reduced by half

    • makes [gametes]

      • [sperm], [eggs]


You have body cells and gametes

sex cells (egg)

body cells

sex cells (sperm)

You have body cells and gametes.

  • Body cells are also called somatic cells.

    • Body cells cannot pass DNA on to offspring

  • Gametes are sex cells: egg and sperm.

    • Gametes have [DNA] that can be passed to offspring.


Your cells have autosomes and sex chromosomes

Your cells have [autosomes] and [sex chromosomes].

  • Your body cells have 23 pairs of chromosomes.

  • Chromosome pairs 1-22 are autosomes.

    • Homologous pairs of chromosomes have the same structure.

    • For each homologous pair, one chromosome comes from each parent.

  • Sex chromosomes, X and Y, determine gender in mammals.


Once again

Once again!

Homologous chromosomes


Body cells are diploid gametes are haploid

Body cells are diploid; gametes are haploid.

  • Diploid (2n) cells have two copies of every chromosome.

    • Body cells are diploid.

    • Half the chromosomes come from each parent.


Lg how do we produce gametes date 2 4 13

  • Haploid (n) cells have one copy of every chromosome.

    • Gametes are haploid.

    • Gametes have 22 autosomes and 1 sex chromosome.

    • [Fertilization] restores the diploid number


Fertilization sperm egg in the fallopian tube oviduct

Fertilization: sperm + egg in the fallopian tube (oviduct)


Meiosis interphase

Meiosis Interphase

The chromosomes have replicated, and they become visible.

http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html


Meiosis prophase i

Meiosis Prophase I

  • The chromosomes are completely condensed. In meiosis (unlike mitosis), the homologous chromosomes pair with one another

  • [Crossing over] occurs

http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html


Crossing over

Crossing over

  • 3 steps

    • cross over

    • breakage of DNA

    • re-fusing of DNA

  • New combinations of traits

Tetrad


Crossing over contd

Crossing over contd.

  • Crossing Over of genes occurs now

    • The exchange of genetic material between homologous chromosomes

    • Results in new genetic combinations of offspring.

    • This is the main advantage of sexual reproduction

Results in Variations!!


Meiosis metaphase i

The homologous chromosomes attach to the spindle fibers. They are preparing to go to opposite poles.

Meiosis Metaphase I

http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html


Meiosis anaphase i

The homologous chromosomes (not chromatids) move to opposite ends of the cell.

Meiosis Anaphase I

http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html


Meiosis telophase i cytokinesis

The cell begins to divide into two daughter cells. It is important to understand that each daughter cell can get any combination of [maternal] and [paternal] chromosomes.

Meiosis Telophase I & Cytokinesis

http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html


Meiosis prophase ii

The cell has divided into two daughter cells.

Meiosis Prophase II

http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html


Meiosis metaphase ii

Just like in Mitosis, the chromosomes line up in the middle on the spindle fibers.

Meiosis Metaphase II

http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html


Meiosis anaphase ii

The two cells each begin to divide. As in Mitosis, the chromatids move to opposite ends of each cell.

Meiosis Anaphase II

http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html


Telophase ii cytokinesis

With the formation of four cells, meiosis is over. Each of these prospective gamete cells carries half the number of chromosomes of somatic cells.

Telophase II &Cytokinesis

http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html


Lg how do we produce gametes date 2 4 13

  • [Gametogenesis] is the production of gametes.

  • Gametogenesis differs between females and males.

    • Sperm become streamlined and motile.

    • Sperm primarily contribute DNA to an embryo.

    • Eggs contribute DNA, cytoplasm, and organelles to an [embryo].

    • During meiosis, the egg gets most of the contents; the other cells form [polar bodies].


Gametogenesis

Gametogenesis


Overview of meiosis

Overview of Meiosis


Meiosis1

Meiosis

  • Meiosis animation:

    http://www.youtube.com/watch?v=D1_-mQS_FZ0&NR=1


Similarities between mitosis meiosis

Similarities between Mitosis & Meiosis

  • Both are forms of nuclear division

  • Both involve [replication]

  • Both involve disappearance of the nuclear membrane

  • Both involve formation of spindle fibers


Comparison of mitosis meiosis

Comparison of Mitosis & Meiosis


Lg how do we produce gametes date 2 4 13

  • Meiosis differs from mitosis in significant ways.

    • Meiosis has two cell divisions while mitosis has one.

    • In mitosis, homologous chromosomes never pair up.

    • Meiosis results in haploid cells; mitosis results in diploid cells.


Mitosis vs meiosis

Mitosis vs. Meiosis


Mitosis vs meiosis1

Mitosis

1 division

daughter cells genetically identical to parent cell

produces 2 cells

2n  2n (diploid)

produces cells for growth & repair

no crossing over

Meiosis

2 divisions

daughter cells genetically different from parent

produces 4 cells

2n  1n (haploid)

produces gametes

crossingover

Mitosis vs. Meiosis


This may help you remember these terms

This may help you remember these terms:

MITosis takes the cell and Makes It Two (diploid)

Meiosis has to do with sex

From the cell’s point of view:

mITosis results in IdenTical Cells

mEioSis results in Egg and Sperm (haploid)

Clyde Freeman Herreid – Dept. of Biological Sciences: Buffalo State Univ. of New York


Putting it all together

46

46

46

46

46

46

46

46

46

46

23

23

46

23

23

Putting it all together…

meiosis  fertilization  mitosis + development

gametes

meiosis

egg

zygote

mitosis &development

fertilization

mitosis

sperm


From one cell to many

EMBRYO

From one cell to many

  • A fertilized egg goes through an early stage of development called an embryo.


Specialized cells perform specific functions

Inner: intestines

Outer: skin cells

Middle: bone cells

Specialized cells perform specific functions.

  • Cells develop into their mature forms through the process of cell [differentiation].

  • Cells differ because different combinations of genes are expressed.


The value of sexual reproduction

The value of sexual reproduction

  • Sexual reproduction introduces genetic variation

    • genetic recombination during meiosis

      • independent assortment of chromosomes

        • random alignment of homologous chromosomes in Meiosis 1

    • crossing over

      • mixing of alleles across homologous chromosomes

    • random fertilization

      • which sperm fertilizes which egg?

  • Driving evolution

    • variation for natural selection


Variation from random fertilization

Variation from random fertilization

  • Sperm + Egg = ?

    • any 2 parents will produce a zygote with over 70 trillion (223 x 223) possible diploid combinations


Sexual reproduction creates variability

Michael & KirkDouglas

Baldwin brothers

Martin & Charlie Sheen, Emilio Estevez

Sexual reproduction creates variability

Sexual reproduction allows us to maintain both genetic similarity & differences.


Words you must know

Words You Must know

  • Mitosis

  • Meiosis

  • Somatic cells

  • Gametes

  • Asexual reproduction

  • Identical

  • Variation

  • Interphase

  • Prophase

  • Genetic material

  • Chromosome

  • Centromere

  • Centrioles

  • Nuclear membrane

  • Metaphase

  • Spindle fibers

  • Homologous chromosomes


Lg how do we produce gametes date 2 4 13

  • Zygote

  • Crossing over

  • Maternal

  • Paternal

  • Gametogenesis

  • Polar bodies

  • Replication

  • Anaphase

  • Telophase/cytokinesis

  • Sexual reproduction

  • Cell division

  • Sperm

  • Egg

  • Autosomes

  • Sex chromosomes

  • Diploid (2n)

  • Haploid (n)

  • Fertilization


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