Meiosis involves two nuclear divisions that result in genetically unique daughter cells. In Meiosis I, homologous chromosomes split but identical sister chromatids remain attached. Meiosis II separates the sister chromatids, reducing the number of chromosomes by half. Special events like crossing over in prophase I and random alignment of homologous chromosomes in metaphase I contribute to genetic diversity between the daughter cells produced in meiosis.

1. Meiosis: Two nuclear divisions
• Meiosis I: Homologous chromosomes
split
– Identical in size, shape, and
genetic information
• Meiosis II: Sister chromatids split
• Special events lead to genetically unique
daughter cells

2. Meiosis

3. Crossing over: Prophase I
• Homologous
chromosomes
switch segments
creating hybrid
chromosomes

4. Random Alignment: Metaphase I
• It is random which microtubule attaches to which
chromosome and ends up in which daughter cell

5. Random Alignment
Example:
• 3 chromosomes
• Random
combination of
chromosomes
from Mom and
from Dad
• 8 different
options

6. Karyotype
• A picture of human chromosomes
• Used to track genetic disorders

7. Nondisjunction
• Failure of chromosomes to separate
correctly in Meiosis
• Results in an aneuploid individual
• If there is one too few chromosomes called
monosomic (2n – 1)
• If one too many chromosomes called
trisomic (2n + 1)

8. Nondisjunction

9. Today
• Online simulation with Karyotypes
• Answer the questions in the lab handout