2. (1) What is Meiosis?
• Cell division for sex-cells.
• Sex Cells:
– Are also called Gametes.
– Sperm in Males
– Eggs in Females
3. (2) What happens during Meiosis?
• There are 2 divisions.
• Start with 1 cell and end up with 4 genetically
unique cells.
• Start “2n” or “Diploid” End “1n” or “Haploid”
• 1n = Haploid = ½ Set of Genetic Information
– In Humans that means that each sperm or egg cell
should have 23 chromosomes.
4. (3) Meiosis Phases
• Meiosis-1:
– Start with 1 cell and end with 2
– Prophase, Metaphase-1, Anaphase-1, Telophase-1,
Cytokinesis-1
– Crossing Over occurs
– Homologous Pairs of Chromosomes
• Meiosis-2:
–
–
–
–
–
Start with 2 cells and end with 4
Metaphase-2, Anaphase-2, Telophase-2, Cytokinesis-2
Pairs of Sister Chromatids
Law of Independent Assortment
Law of Segregation
5.
6. (4) Meiosis-1 Details
• Prophase:
Chromosomes form + Nucleus dissolves.
• Metaphase-1:
Homologous pairs of chromosomes line up at the metaphase
plate.
Crossing Over occurs.
• Anaphase-1:
Homologous pairs of chromosomes separate.
• Telophase-1:
Chromosomes are fully separated.
• Cytokinesis-1:
Cytoplasm splits and the cell membranes divide.
7. (5) Meiosis-1 Vocabulary:
• Homologous Pairs of Chromosomes
– Pairs of sister chromatids with similar segments of DNA
(or genes.)
– Looks like 2 X’s.
• Crossing Over
– When nearby chunks of DNA are exchanged between
homologous pairs of chromosomes.
– Used to increase genetic diversity.
8. (6) Meiosis-2:
• Metaphase-2:
Pairs of sister chromatids line up at the metaphase plate.
• Anaphase-2:
Pairs of sister chromatids separate.
Law of Segregation.
Law of Independent Assortment.
• Telophase-2:
Chromosomes are fully separated.
Nuclei reform.
• Cytokinesis-2:
Cytoplasm splits and the cell membranes divide up.
10. (7) Meiosis-2 Vocabulary:
• Sister Chromatids:
Identical copies of chromosomes.
• Law of Segregation:
Chromosomes split up so that each sex cell
receives a different variation of each gene.
• Law of Independent Assortment:
Chromosomes split up completely independent of
every other chromosome and gene variation.
12. (8) Meiosis Errors
• When chromosomes do not separate correctly
during meiosis this can cause:
– Sex Cells to have too many chromosomes (more than
23).
– Sex cells to have too few chromosomes (less than 23).
• Individuals born from these sex cells will acquire a
genetic disorder from having the wrong number of
sex chromosomes.
