Download Meiosis - Mercer Island School District

Meiosis
Meiosis is the type of cell division for that produces the
______________ cells ( ______________ ) which are also
known as gametes.
Two important characteristics of meiosis is that it reduces
the number of chromosomes to half of the parent cell and
it creates ___________________.
Somatic Cells vs. Gametes
Somatic cells are body cells (nerve cells, muscle
cells, epithelial cells…).
These cells all have different appearances and
functions but have the same genetic information.
Gametes are the reproductive cells - the egg or the
sperm.
Gametes __________________________________
_______________________.
If Meiosis Did NOT Occur
If two parental cells combined that had the
parents full set of 46 chromosomes:
The first generation of offspring would have____
chromosomes.
The next generation of offspring would have ____
chromosomes…
Homologous Chromosomes
Most cells in a human (and in most eukaryotic organisms)
contain two copies of each chromosome.
These chromosomes are not identical (one is from the
mother and one from the father), but they ________
_______________. These pairs are called homologous
chromosomes.
Homologous chromosomes may contain different forms
of a gene for the same trait.
Brown eyes
Green eyes
Humans have 23 pairs of chromosomes, for a
total of 46 chromosomes in each somatic (body)
cell.
Autosomal chromosomes: Chromosomes 1-22, which
form homologous pairs in both males and females.
Sex chromosomes: Chromosome 23. Determines
gender (XX= female, XY= male). For males, this pair is
not homologous (different length and type of genes).
Diploid and Haploid Cells
Diploid cells have homologous
pairs of chromosomes. (2 of each
chromosome)
Human somatic (body) cells are
diploid. (di = 2)
Haploid cells ______________
_______________________.
Gametes (egg and sperm) cells
are haploid.
When fertilization occurs (fusion of egg and
sperm) the diploid number is restored.
Video: Diploid vs. Haploid Cells
http://www.youtube.com/watch?v=MU83VWAvUf4&list=PLF8D6A5276A9A092F
Diploid cells are represented by 2n and
haploid by n, where n is the number of
different chromosomes.
Examples:
Organism
Human
Gamete (n)
23
Body cell (2n)
46
Pea Plant
7
___
Fruit Fly
__
8
Dog
39
___
Indian Fern
____
1260
Chromosome number in
different organisms
http://morgan.rutgers.edu/morganwebframes/l
evel1/page2/ChromNum.html
Discuss with your table partner:
Compare and contrast mitosis with meiosis.
What are homologous chromosomes? What kind of
cells have homologous chromosomes?
What do the terms diploid and haploid mean? What
kind of cells are diploid? What kind of cells are
haploid?
Interpreting Genetics Diagrams
Homologous chromosomes are indicated by length.
Sister chromatids (identical copies produced during S phase
of interphase) are shown connected by centromere.
Genes on the chromosome are represented with letters.
Example: R/r represents gene for pea seed shape
Different forms of the same gene are represented with
capital versus lower case letters.
Example: R represents round shape form of the gene, r
represents wrinkled shape form of the gene.
Overview of Meiosis
In meiosis, __________________ of
chromosomes is followed by ___cell divisions,
to produce __ __________cells.
Phases of Meiosis
As with mitosis, meiosis is preceded by
an interphase period,
during which the chromosomes are
duplicated.
The two sister chromatids are
___________________.
The homologous pairs have the
same genes, but could have
different alleles (forms of the
gene).
At the start of meiosis, there are
____ copies of each gene.
Prophase I
During Prophase I,
the chromosomes
condense to become
visible.
______________________
_______________________
_______________________
(Homologous pairs never form tetrads during
mitosis).
Metaphase I
In metaphase I,
the _______________
__________ line up along
the middle of the
spindle.
Anaphase I:
HOMOLOGOUS PAIRS
separate.
Telophase I
Nuclei reform, producing
2 haploid daughter cells.
But each cell still has ___
______________________
______________________
Meiosis II separates the sister chromatids.
Prophase II
Anaphase II
Metaphase II
Telophase/
cytokinesis II
Meiosis Video
http://www.youtube.com/watch?v=D1_-mQS_FZ0
Meiosis Animation
http://www.cellsalive.com/meiosis.htm
Genetic Variation from Meiosis
Meiosis is important for providing genetic
variation because it allows for genetic
recombination- new combinations of genes.
Parental
combinations
Recombinants
Sources of Genetic Variation from Meiosis
Independent Assortment:
Each homologous pair lines up independently on the
spindle in Meiosis I. So all of the possible
arrangements of chromosomes are ______________
if two genes are on different chromosomes.
In humans
there are 223
possible
chromosome
combinations
from each
parent.
If an organism has gene forms Y and y on one
homologous pair, and R and r on a different homologous
pair, then due to independent assortment the gametes
produced will be 25 % YR, 25% yr, 25% Yr and 25% yR
http://www.youtube.com/watch?v=kZyK2eWhpfQ
Independent Assortment Video
http://www.sumanasinc.com/webcontent/animations/content/independentass
ortment.html
Sources of Genetic Variation from Meiosis cont.
Crossing Over:
During prophase I, strands of ____________
_____________ can be exchanged while the
homologous pair are joined in tetrads.
Crossing over allows
recombination of
genes on the ______
_________________
Crossing Over Video
http://www.youtube.com/watch?v=op7Z1Px8oO4
Crossing over animation
Discuss with your table partner:
Compare and contrast mitosis with meiosis.
Fill in the chart on the next slide for these two
different types of cell division.
Comparing Mitosis and Meiosis
MITOSIS
MEIOSIS
Purpose
______
_________
Location
__________
___________
________
__________
___________
____________
_
_
_
_
# of DNA
replications
# of cell
divisions
#/type of cells
produced
__ _______cells __ _______ cells
Comparing Mitosis and Meiosis Video
http://www.youtube.com/watch?v=Ba9LXKH2ztU
Additional Meiosis Overview Video (5.5 min.)
http://www.youtube.com/watch?v=-DLGfd-Wpr4
Comparing Mitosis and Meiosis Cont.
NOVA site comparing mitosis and meiosis.
Spermatogenesis: produces
four ____ sperm cells
through meiosis. A greater
quantity of sperm is
produced, but each sperm
has less stored energy.
Oogenesis (egg production):
meiotic division produces 1
larger egg which receives
______________________
______________ of the
parent cell. The other three
Fewer eggs need to be produced
cells produced in the
energy is invested per egg
meiotic division are smaller more
(mitochondria etc.).
polar bodies.
so