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BELL WORK
Current Event
Complete the following tasks:
1. Read the Current Event
– New Chemistry May Cure Human Cancers
2. Answer the Questions
– What facts about cells did scientists use to
design their treatment
– How did it work?
Week of April 21, 2014
HOMEWORK
Friday, April 25, 2014
• MP3 Recording
–
–
–
–
Meiosis – Mitosis Comparison
Listen to Recording
Take Quiz and Print for Credit
Put in Folder
• BioFlix
– Finish
– Place in Folder
• Folders
– Complete – after Karyotyping Lab next week
Friday Agenda
• Vocabulary Quiz
• BioFlix Meiosis
– Animation
– Tutorials
– Worksheet
• Absent?
– See Me for Details
Meiosis Basic Notes
Just Add Note Cards
Meiosis
Parent cell –
chromosome pair
Chromosomes
copied
1st division - pairs split
2nd division – produces
4 gamete cells with ½
the original no. of
chromosomes
Reduction Division
THE STAGES OF MEIOSIS:
Meiosis I : Separates
Homologous Chromosomes
• Interphase
– Each of the chromosomes replicate
– The result is two genetically identical
sister chromatids which remain
attached at their centromeres
Interphase I
• Nucleus and nucleolus visible.
chromatin
nuclear
membrane
cell membrane
nucleolus
Prophase I - Synapsis
Homologous chromosomes
sister chromatids
Tetrad
sister chromatids
Homologous Chromosomes
• Pair of chromosomes (maternal and paternal) that are similar in
shape and size.
• Homologous pairs (tetrads) carry genes controlling the same
inherited traits.
• Each locus (position of a gene) is in the same position on
homologues.
• Humans have 23 pairs of homologous chromosomes.
22 pairs of autosomes
1 pair of sex chromosomes
Homologous Chromosomes
eye color
locus
eye color
locus
hair color
locus
hair color
locus
Paternal
Maternal
Karyotype
• A method of organizing the chromosomes of a cell in
relation to number, size, and type.
Humans have 23 Sets of Homologous Chromosomes
Each Homologous set is made up of 2 Homologues.
Homologue
Homologue
Autosomes
(The Autosomes code for most of the offspring’s traits)
In Humans the
“Autosomes”
are sets 1 - 22
Sex Chromosomes
The Sex Chromosomes code for the sex of the offspring.
** If the offspring has two “X” chromosomes it will be a female.
** If the offspring has one “X” chromosome and one “Y” chromosome it will be a
male.
In Humans the
“Sex
Chromosomes”
are the 23rd set
XX chromosome - female
XY chromosome - male
Boy or Girl? The Y Chromosome “Decides”
Y chromosome
X chromosome
Sex Chromosomes
“Sex
Chromosomes”
…….the 23rd set
23
This person has 2
“X” chromosomes…
and is a female.
Interphase I
• Nucleus and nucleolus visible.
chromatin
nuclear
membrane
cell membrane
nucleolus
Prophase I
• This is a crucial phase for mitosis.
• During this phase each pair of
chromatids don’t move to the equator
alone, they match up with their
homologous pair and fasten together
(synapsis) in a group of four called a
tetrad.
• Extremely IMPORTANT!!! It is during this
phase that crossing over can occur.
• Crossing Over is the exchange of
segments during synapsis.
Prophase I
spindle fiber
aster
fibers
centrioles
Metaphase I
• The chromosomes line up at the
equator attached by their
centromeres to spindle fibers from
centrioles.
– Still in homologous pairs
Metaphase I
OR
metaphase plate
metaphase plate
Anaphase I
• The spindle guides the movement of the
chromosomes toward the poles
– Sister chromatids remain attached
– Move as a unit towards the same pole
• The homologous chromosome moves
toward the opposite pole
– Contrasts mitosis – chromosomes appear as
individuals instead of pairs (meiosis)
Anaphase I
Telophase I
• This is the end of the first meiotic cell
division.
• The cytoplasm divides, forming two
new daughter cells.
• Each of the newly formed cells has
half the number of the parent cell’s
chromosomes, but each chromosome
is already replicated ready for the
second meiotic cell division
Cytokinesis
• Occurs simultaneously with
telophase I
– Forms 2 daughter cells
• Plant cells – cell plate
• Animal cells – cleavage furrows
• NO FURTHER REPLICATION OF
GENETIC MATERIAL PRIOR TO
THE SECOND DIVISION OF
MEIOSIS
Telophase I
Meiosis II :
Separates sister chromatids
• Proceeds similar to mitosis
• THERE IS NO INTERPHASE II !
Prophase II
• same as prophase in mitosis
Metaphase II
• same as metaphase in mitosis
metaphase plate
metaphase plate
Anaphase II
• same as anaphase in mitosis
• sister chromatids separate
Telophase II
• Same as telophase in mitosis.
• Nuclei form.
• Cytokinesis occurs.
• Remember:
four haploid daughter cells
produced.
gametes = sperm or egg
Telophase II
One Way Meiosis Makes Lots of
Different Sex Cells (Gametes) –
Independent Assortment
Independent assortment produces 2n
distinct gametes, where n = the number
of unique chromosomes.
In humans, n = 23 and 223 = 6,000,0000.
That’s a lot of diversity by this
mechanism alone.
Another Way Meiosis Makes Lots of Different
Sex Cells – Crossing-Over
Crossing-over multiplies the already huge number of different gamete
types produced by independent assortment.
The Key Difference Between Mitosis and Meiosis is
the Way Chromosomes Uniquely Pair and Align in
Meiosis
Mitosis
The first (and
distinguishing)
division of meiosis
Boy or Girl? The Y Chromosome “Decides”
Y chromosome
X chromosome
Boy or Girl? The Y Chromosome “Decides”
ANY QUESTIONS?
EXTRA SLIDES
Meiosis – division error
Chromosome pair
Meiosis error - fertilization
Should the gamete with the
chromosome pair be fertilized
then the offspring will not be
‘normal’.
In humans this often occurs
with the 21st pair – producing
a child with Downs Syndrome
21 trisomy – Downs Syndrome
Can you see the
extra 21st
chromosome?
Is this person male
or female?