Meiosis
Sexual Reproduction
Why is meiosis important?
• Make eggs and sperm for reproduction
• Genetic diversity – half DNA from father and
half from mother= new combination
• Somatic cells – (any cell other than egg or
sperm)-formed from mitosis only – Have 46 chromosomes and divide to make
identical cells with 46 chromosomes
– Diploid (2n)
• Gametes (egg and sperm) – formed from
meiosis only
– Have 23 chromosomes
– Haploid (n)
• Autosomes are the 22 pairs (44) of
chromosomes that are not involved in
determining gender
• Sex chromosomes are the pair (2) that
determine gender
• Homologous chromosomes- pair of
chromosomes that are similar in size, shape,
and genetic content- one in each pair comes
from the father and the other from the
mother.
• Humans have ____pairs of homologous
chromosomes.
Chromosome Numbers in Cells
• Diploid (2n) cell contains 2 sets of
chromosomes (somatic cell)
• Haploid (n) cell contains 1 set of chromosome
(gamete)
• What happens when 2 haploid cells fuse in
fertilization?
Homologous Chromosomes and Sister
chromatids
Mitosis vs Meiosis
• Mitosis – used for Growth
–
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Two daughter cells
genetically identical to parent cell
two full sets of chromosomes (diploid)
makes bigger organism
• Meiosis – used for Reproduction
–
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Four daughter cells
genetically different from parent cell (and each other)
one full sets of chromosomes (haploid)
helps makes another organism (sexual reproduction)
Meiosis- two cell divisions
Meiosis preceded by an interphase (just like mitosis) – chromosomes replicated during
the S phase.
Meiosis 1
Stages of Meiosis
Crossing Over in Action
How does this differ from metaphase
in mitosis?
Independent Assortment
After the 1st
Division
• http://highered.mcgrawhill.com/sites/0072495855/student_view0/ch
apter28/animation__unique_features_of_mei
osis.html
• Features unique to meiosis
Mitosis versus Meiosis
What happens to the possible
combinations when crossing over occurs?
Sperm versus the Egg