Mitosis= reproduction of body cells (SOMATIC CELLS) Meiosis= reproduction of sex cells (sperm and...
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Transcript of Mitosis= reproduction of body cells (SOMATIC CELLS) Meiosis= reproduction of sex cells (sperm and...
Mitosis= reproduction of body cells (SOMATIC CELLS)Meiosis= reproduction of sex cells (sperm and eggs)
Sex Cells (GAMETES) = reproductive cells produced in sex organs (testes/ovaries)
Reduces chromosome number from DIPLOID (2n) down to HAPLOID (n)
Why do sex cells have only half the genetic information of body cells?
46Body Cell
46 46
92!
MITOSIS
Body Cells One Division Create 2 identical
cells Copies have the exact
same number of chromosomes
46 chromosomes in every body cell
Paired chromosomes
MEIOSIS
Sex Cells (egg and sperm)
Two Divisions Creates 4 cells Copies has half the
number of chromosomes
23 chromosomes in a sperm or egg cell
NOT in pairs
Meiosis Overview Video
Chromosomes
Chromatids
• All male sperm is genetically different from one another
• All female eggs are genetically different from one another
• When they fuse in fertilization, the chromatids combine to make a new individual!
HOMOLOGOUS (“same”) pairs of chromosomes = same sized chromosomes that carry the same genes
PROPHASE I
Chromosomes coil up and become visible
Nuclear membrane and the nucleolus disappear
Spindle fibers form Centrioles begin to move to
opposite sides HOMOLOGOUS
CHROMOSOMES pair up and CROSSING OVER occurs.
CROSSING OVER
Chromosomal material is exchanged between sister chromatidsAllows for genetic variation!
Then, paired chromosomes line up in the center for metaphase I
ANAPHASE I
Homologous chromosomes split and move to opposite ends
This is where the chromosome number is divided in half (2n n)
TELOPHASE I
Cleavage furrow forms Cytokinesis occurs Nuclear membrane
DOES NOT reform Chromosomes DO NOT
go back to chromatin 2 daughter cells have
been created with the haploid number of chromosomes
Meiosis I Animation
Centrioles move apart Spindle forms between
centrioles Sister chromatids line up in the
middle of cell Fibers pull sister chromatids
apart Nuclear membrane and
nucleolus reform Cell membrane pinches in and
divides in the cytoplasm End Result: 4 sex cells (different than what started out
with!!)
Keeps the number of chromosomes the same from one generation to the next Human sperm cell + Human
egg cell= zygote▪ 23 chromosomes + 23
Chromosomes= 46 chromosomes Provides genetic variation
Why you don’t look exactly like your siblings
http://www.cellsalive.com/meiosis.htm
http://www.youtube.com/watch?v=D1_-mQS_FZ0&feature=related
http://www.youtube.com/watch?v=MyXvx5FkfTE&feature=related
Can you find the homologous pairs?
How many homologous pairs do you see?
Males – Meiosis is called SPERMATOGENESIS 4 equally sized sperm
produced Cytoplasm divides evenly Ongoing in testes
throughout a male’s life Human males produce
approximately 1000 sperm per second (30 billion/year).
Females – Meiosis is called Oogenesis 4 cells, but only 1
becomes an egg Uneven cytokinesis – 1
cell receives most of the cytoplasm = EGG (needs extra cytoplasm to accommodate fertilization)
Other 3 cells receive very little cytoplasm and die off = POLAR BODIES
Meiosis in human females begins before person is born but stops in prophase I and does not resume until after puberty.
Each month, approximately 1000 primary oocytes will mature but most will die.
Ovulation occurs approximately once every 28 days. Females ovulate approximately 400 times during their lifetime
Women are born with all of the primary oocytes that they will ever have (2 million). At puberty, there are approximately 400,000 left.
Compare Mitosis and Meiosis http://www.pbs.org/wgbh/nova/
miracle/divi_flash.html