Why is it important that meiosis produces haploid cells?
What is a tetrad?
What stage of meiosis can crossing over occur in?
Why is crossing over important?
• Go over Vocabulary set #2 Definitions
• Go over Section 8-2 Review Worksheet
• Notes: Meiosis
• Complete Meiosis Skill Worksheet

•
Binary fissiona form of asexual reproduction in prokaryotes
•
Mitosis - process of cell division that forms two new nuclei each with the same number of chromosomes
• Asexual reproductionreproduction that does not involve the union of gametes; offspring are genetically identical to parent
• Meiosis - process of cell division during which the number of chromosomes decreases to half the original number by two divisions of the nucleus
• Gametereproductive cell; sperm or egg
• Cell platethe precursor of a new plant cell wall that forms during cell division
• Cytokinesisdivision of cytoplasm
• Spindle fiberone of the microtubules that assist in the movement of chromosomes in dividing eukaryotic cells
• Synapsispairing of homologous chromosomes during meiosis
• Tetradfour chromatids in a pair of homologous chromosomes that come together as a result of synapsis
•
Crossing-overthe exchange of genetic material between homologous chromosomes during meiosis that results in genetic diversity
•
Genetic recombinationregrouping of genes in offspring that results in a genetic makeup different than parents
• Independent assortmentrandom distribution of the genes to gametes
• Spermatogenesisthe process by which male gametes form
• Oogenesisthe process by which female gametes form
• Polar bodya short lived product of the formation of gametes by meiosis
• Sexual reproductionreproduction in which gametes fuse

• Meiosis produces haploid (n) gametes so that after fertilization, the embryos will be diploid.
• Meiosis also permits recombination (crossing over) so that each new gamete will have genes from both mother and father.

Prophase I Metaphase I Anaphase I Telophase I
Homologous chromosomes synapse or pair.
(tetrad)
Crossing over occurs. Spindle fibers form.
Microtubule spindle apparatus attaches to chromosomes.
Homologous pairs align along spindle equator.
Homologous pairs of chromosomes separate and move to opposite poles.
One set of paired chromosomes arrives at each pole, and nuclear division begins.

Prophase II Metaphase II Anaphase II Telophase II
Chromosomes recondense.
Spindle fibers form between centrioles (if present).
Microtubule spindle apparatus attaches to chromosomes.
Chromosomes align along spindle.
Sister chromatids separate and move to opposite poles.
Chromatids arrive at each pole, and cell division begins.
4 haploid daughter cell.
Genetically different due to independent assortment.

Crossing-over happens in early prophase I of meiosis.

Homologous pair of chromosomes (schematized)
Centromere
A
B
C C
B
A a b c
F
E
D D
E
F c a b f e d d e f
Sister chromatids

A
B
C C c c a b
F
E
D D
E
F f e d d e f
Chiasma

A
B
C C b a
A
B c a c b
F
E
D D
E
F f e d d e f

• Why is it important that meiosis produces haploid cells?
• What is a tetrad?
• What stage of meiosis can crossing over occur in?
• Why is crossing over important?

Agenda
How is spermatogenesis different than oogenesis?
What is a polar body?
• Vocabulary Review Game
• Notes
• Read Lecture Four: Sexual Evolution: From X to Y
• Web Activity
• Complete Essay
Don’t forget Vocabulary Set #2 Quiz is Wednesday!

Spermatogenesis- Production of sperm cells
• Produces four haploid sperm cells

Oogenesis- Production of mature egg cells or ova
• Produces one haploid egg cell and 3 polar bodies which degenerate

Recombination happens here

(mitosis ends here)

Review
How is spermatogenesis different than oogenesis?
What is a polar body?
• Read Lecture Four: Sexual Evolution: From X to Y
• Web Activity:Log onto Howard Hughs Medical
Institute Website and select “Gender Testing for
Female Athletes” http://www.hhmi.org/biointeractive/gender/index.html
• Complete Essay