1. Meiosis
Producing Sex Cells

2. I. How Many Possible Chromosome combos?
In a human gamete:
23 pairs of chromosomes
- one from each pair in a sperm or egg.

3. If there were only one pair, how many ways would there be to pass on one chromosome?
From two pairs?
Three pairs?
Hmmm, I see a pattern…
And where there’s a pattern, there’s a formula.

4. The equation F(x)= 2x X = # of pairs. Possible combinations is…
2 to choose from in each pair.
Possible combinations is…
8,388,608
Finally: For 2 of those cells to combine?
(8,388,608)2

5. Meiosis Produces sex cells - gametes
Somatic (body) cells have pairs of homologous chromosomes. Same genes at same locus (location).
These are Diploid – 2n
N is number of each chromosome type.
Humans: 2n = 46
Gametes: n = 23.
Haploid cells
That’s a lot of vocab
Bro!

6. Karyotype Photograph that shows all pairs.
Can diagnose extra/missing chromosomes/fragments.
Down Syndrome, Klinefelter, etc

7. Quick Quiz Llama sperm/egg cells have 38 chromosomes.
What is the N #? 2N?
Are sperm haploid or diploid?

8. Meiosis I cell’s DNA is copied (4n) Tetrad – 4 chromatids line up
During Prophase I

9. Crossing Over
A piece of one chromosome is cut out, switching with the same piece on its homolog.
Recombinant chromosomes.
Creates new genetic combinations. Chances of identical gametes is basically zero.

10. Meiosis I Like Mitosis Chrom. separated into 2 cells.
Sister chrom. still together.

11. Meiosis II Sister chr. are pulled apart.
Cell divides again. 4 total cells produced.
Each has n number.

12. Mistakes During Meiosis
Nondisjunction
Failure of a pair of chromosomes to separate correctly.
Spindle fails to attach properly at centromere. Result: both chromatids go one way. Nondisjunction.
Gamete with too many/few chromosomes. Usually lethal.
Down Syndrome - 3 copies
(Trisomy) of chr. 21.

14. Sex- Chromosomes XXY - Kleinfelter syndrome XO - Turner Syndrome
Male sex organs, testes abnormally small, sterile.
Breast enlargement, normal intelligence.
How Frequent?
1 per 1000 male births.
XO - Turner Syndrome
Lacking an X. Develops as a woman
Short stature
Sterile because sex organs don’t fully mature.
Frequency: 1 per 2500 female births.