Meiosis
Ms. Wheeler
Unit 6
Meiosis
›  Produces
haploid gametes (egg and sperm) in
sexually reproducing organisms
›  Why do gametes have to be haploid?
›  Fertilization
of gametes creates a diploid organism
Fertilization
Meiosis
›  2
Stages
›  Meiosis
I – separates homologous chromosomes
›  Meiosis II- separates sister chromatids (mitosis)
›  2
divisions total to cut the number of chromosomes
in half
Meiosis I
Meiosis II
Meiosis I
Meiosis II
Genetic Variability
›  Every
1. 
2. 
3. 
person is different due to 3 factors
Independent assortment- the random
arrangement of homologous chromosome pairs
during metaphase I.
Crossing over- pieces of chromosomes swap
during prophase I.
Random fertilization- each fertilization
combination of egg and sperm would create a
different outcome.
1. Independent Assortment
›  Homologous
chromosomes arrange themselves in a
random manner during metaphase I of meiosis
2. Crossing Over
›  Homologous
chromosomes exchange pieces of
genetic information during prophase I of meiosis.
2. Crossing Over
3. Random Fertilization
›  Any
one sperm can fuse with and fertilize any one
egg at random.
Sperm cells
Egg cells
Comparing Mitosis & Meiosis
Mitosis
›  Produces
somatic cells
›  1 cell division
›  Produces 2 genetically
identical cells
›  Sister chromatids
Meiosis
›  Produces
gametes
›  2 cell divisions
›  Produces 4 genetically
different cells
›  Homologous pairs
(meiosis I)