Meiosis
Genetic Diversity
Meiosis Vocabulary
Somatic cell- a body cell (liver, skin, testis, ovary).
Diploid- chromosomes are paired (2 # 9 chromosomes)
2n- symbol for diploid
Gamete- sex cells (only 2 types: sperm & egg)
Haploid- a single chromosome
n- symbol for haploid
Homologous chromosomes- same (all # 9
chromosomes)
Homologous Chromosomes
Homo= same
• Same length
• Centromere same
location
• Same position of genes
How many different
chromosomes are
Represented in the image above?
Chromosome #1 –
Mom and its copy
Chromosome #1 –
Dad and its copy
Significance of Meiosis
Increases the genetic diversity
of a gene pool.
Gene pool- all the possible genetic possiblities
with a population.
1. Crossing over- Prophase I
2. Independent Assortment- Metaphase I
3. Random fertilization -
Meiosis is Reduction Division
What is reduced?
Meiosis Amoeba sisters - 7 min
Same parents: Different children?
Genetic Diversity- Meiosis
• Crossing – Over
• Independent Assortment
As a result of Meiosis:
• Random fertilization
Genetic variation- Meiosis I
Crossing Over- Prophase I
Homologous chromosomes – exchange genes.
This process is random -- occurs with all
23 different homologous pairs- different
Every time!
Crossing Over
Enzymes cut genes out of the two different
versions homologous chromosomes and
exchange them.
Independent Assortment
Homologous chromosomes line up randomly on
the equator.
During Anaphase- they will “sort out” differently
into cells.
Independent assortment can generate
up to 223 genetic variations in the
gametes.
Genetic variation- Meiosis I
Independent Assortment- Metaphase I
Gametes are all genetically
different!
Remember- each child is a product of a separate
meiotic event for both the sperm and the egg (ovum).
Each child was the result of a different
meiosis event for Mom & Dad
Genetic Variation - Gametes
Random Fertilization
Which sperm will fertilize the ovum.
Review the Process
What type of reproductions is Meiosis?
How many times will the cell divide?
How many times will the DNA replicate?
How many cells are produced?
Are the daughter cells clones?
Diversity is the raw material of
Evolution
What would happen to
the offspring is suddenly
an alien came to their
community and
devoured people with
white hair?
Why is “sex” (the exchange of genetic information) more
important than life?
Evolution
Variations in a species- makes it more
likely that some organisms will
survive in a changing environment!
How does Meiosis factor into the
evolutionary process?
Evolution
Genetic Variation is the raw material for
evolution!!
Differentiate between Crossing over
and Independent assortment:
1. What happens with homologous chromosomes in
crossing over?
•
When does it occur (very specific)?
• What is the result?
2. What happens with homologous chromosomes in
Independent Assortment?
• When?
• What is the result?
Chromosome Mutations
Crossing Over
Cutting and Pasting Errors:
Errors in Anaphase
What happens to the chromosomes in
Anaphase?
Have you ever been told to move to the right
but you moved to the left?
Sometimes this happens to the chromosomes!
Non-disjunction Disorders
Chromosomes fail to separate properly!
Creates some cells with :
• too many chromosomes!
• too few chromosomes!
Down’s Syndrome