1. Meiosis Mitosis Cuts chromosome number in half
Forms sex cells or gametes (sperm and egg)
Mitosis
equal division
forms body or somatic cells

2. Human’s have 23 homologous pairs of chromosomes
Figure: 09-07
Title: A Karyotype Displays a Full Set of Chromosomes
Caption: One member of each chromosome pair comes from the individual’s father and the other member from the mother. Each paired set of chromosomes is said to be “homologous,” meaning the same in size and function. (The two chromosomes over the number 1 are a homologous pair, the two over number 2, and so forth.) Homologous chromosomes are not exactly alike, however; the genes on them may differ somewhat, meaning the effects they produce will differ. Notice that this karyotype set is from a human male; there are 22 pairs of homologous chromosomes and then one X and one Y chromosome (which are not homologous). A female would have two X chromosomes. All the chromosomes are in the duplicated state.

3. One DNA double helix, one chromosome, one chromatid
Review from DNA Replication Lecture
Old half of DNA
Old half of DNA
New nucleotides
Two DNA double helices, one chromosome, two chromatids
Review from Mitosis Lecture
Chromosome with two chromatids

4. Ploidy = number of chromosome sets in a cell
Haploid (1N) = one set of chromosomes
Diploid (2N) = two sets of chromosomes

5. Each member of the homologous pair was inherited from either a person’s male and female parent.
Figure: 09-07
Title: A Karyotype Displays a Full Set of Chromosomes
Caption: One member of each chromosome pair comes from the individual’s father and the other member from the mother. Each paired set of chromosomes is said to be “homologous,” meaning the same in size and function. (The two chromosomes over the number 1 are a homologous pair, the two over number 2, and so forth.) Homologous chromosomes are not exactly alike, however; the genes on them may differ somewhat, meaning the effects they produce will differ. Notice that this karyotype set is from a human male; there are 22 pairs of homologous chromosomes and then one X and one Y chromosome (which are not homologous). A female would have two X chromosomes. All the chromosomes are in the duplicated state.

6. 23 + 23 = 46 homologous chromosomes
Sperm, 1N egg, 1N
23 chromosomes
23 chromosomes
= 46 homologous chromosomes
Zygote = 2N cell

7. Same cell after DNA replication
Sperm, 1N egg, 1N 1 1’ 2 2’ 1’ 1
Eye Dark
Eye light
1 and 1’ = homologous chromosomes
Same cell after DNA replication 1’ 1’ 1 1
Zygote = 2N cell 2 2’ 2 2’

8. Zygote (2n) Mitosis Adult Cells (2n) Meiosis Meiosis Fertilization
Human = chromosomes
Mitosis
Adult Cells (2n)
Human = 46
Meiosis
Meiosis
Fertilization
Sperm (1n gamete)
Egg (1n gamete)
Sperm = chromosomes
Egg = chromosomes

9. Meiosis =
One 2N cell forms four 1N cells
Mitosis =
One 2N cell forms two 2N cells

10. Mitosis Meiosis 1 1’ 1 2N 2’ 2 2N 2 1’ 1 1’ 2’ 1N 1N 2 2’ 2’ 2 2’ 2 1’

11. Crossing over =
Exchange of genetic material between chromatids on homologous chromosomes …... Only in meiosis

12. Homologous Chromosomes Recombinant Chromatids1
Homologous Chromosomes 1’ 1
Crossing over 1’
Recombinant Chromatids

13. Chiasmata = cross-overs

14. Which one can have crossing over?
Mitosis
Meiosis 1 1’
Which one can have crossing over? 1 2N 2’ 2 2N 2 1’ 1 1’ 2’ 1N 1N 2 2’ 2’ 2 2’ 2 1’ 1 2’ 1 1 2 1’ 2’ 2 1 1’ 1’ 1N 1N 1N 1N 2N 2N

15. Crossing over occurs in meiosis because homologous chromosomes are next to each other.
Review

16. Summary Mitosis – 1, 2N cell makes 2, 2N Cells
Review
Summary
Mitosis – 1, 2N cell makes 2, 2N Cells
Meiosis – overall; 1, 2N cell makes 4, 1N cells