Meiosis - Mercer Island School District · 2013-11-19 · Meiosis Meiosis is the type of cell...
Transcript of Meiosis - Mercer Island School District · 2013-11-19 · Meiosis Meiosis is the type of cell...
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=MU83VW
AvUf4&list=PLF8D6A5276A9A092F
Diploid cells are represented by 2n and
haploid by n, where n is the number of
different chromosomes.
Examples:
Organism Gamete (n) Body cell (2n)
Human 23 46
Pea Plant 7 ___
Fruit Fly __ 8
Dog 39 ___
Indian Fern ____ 1260
Chromosome number in different organisms
http://morgan.rutgers.edu/morganwebframes/level1/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 Metaphase II
Anaphase II Telophase/
cytokinesis II
Meiosis Video http://www.youtube.com/watch?v=D1_-mQS_FZ0
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
Independent Assortment Video
http://www.youtube.com/watch?v=kZyK2eWhpfQ
http://www.sumanasinc.com/webcontent/animations/content/independentassortment.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-W
pr4
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
cells produced in the
meiotic division are smaller
polar bodies.
Fewer eggs need to be produced so more energy is invested per egg (mitochondria etc.).