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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)
slide7

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.
slide20
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
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

slide34
[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].
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
slide41
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 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
slide52

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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