1. Reproduction, Mitosis, Meiosis
Reproduction can be: SEXUAL OR ASEXUAL
Asexual Reproduction:
requires only 1 parent
offspring are exact copy of the parent: a clone
No genetic variety in the population: organisms are “copies” of the original.
Example: Binary Fission
divide into two equal halves
Single cell organisms

2. Sexual Reproduction Requires sex cells (gametes, egg and sperm)
Requires fertilization (when gametes combine)
produces a greater chance of variation (diversity) within a species than asexual reproduction would.
improves the chances that a species will adapt to his environment and survive.

3. Sexual vs. Asexual Reproduction
Asexual reproduction results in offspring that are genetically identical to the parent organism. Needs 1 parent.
Sexual reproduction results in offspring that are genetically different from the parent organisms. Needs 2 parents.

4. First…
Chromosomes

5. X and Y, determine gender in mammals.
Chromosomes and Meiosis
two types of chromosomes:
Autosomes found in body cells (diploid, 2 copies, 2N)
sex chromosomes found in sex cells (haploid, 1 copy, N)
Humans:
body cells have 23 pairs or 46 (2N) chromosomes
Sex cells have 23 (N) chromosomes
X and Y, determine gender in mammals.
XX = female
XY = male
Chromosome pairs 1-22 are autosomes.

6. same pair. Same size Same shape
BUT NOT IDENTICAL: genes are different versions of the same trait!
Ex. Eye color

7. Now…
MEIOSIS

8. Mitosis
- occurs in somatic cells
makes 2 diploid cells
Produces genetically Identical cells
Meiosis
occurs in sex cells (gametes)
makes 4 haploid cells
produces genetically different cells

9. DIPLOID
DIPLOID
MEIOSIS
SPERM
EGG
(HAPLOID)
(HAPLOID)
DIPLOID

10. PMAT I: prophase 1 metaphase 1 anaphase 1 telophase 1 Main Events:
2 PARTS IN MEIOSIS:
homologous chromosomes
sister
chromatids
MEIOSIS I
PMAT I: prophase 1 metaphase 1 anaphase 1 telophase 1
Main Events:
crossing over occurs (Prophase I)
pairs of homologous chromosomes separate (Anaphase I)
MEIOSIS II
PMAT II: prophase 2 metaphase 2 anaphase 2 telophase 2
- Main Event: sister chromatids separate (Anaphase 2)

11. Meiosis I Independent assortment! MEIOSIS I Chromosomes condense
CROSSING OVER occurs during synapsis (when chromosomes pair up to exchange pieces)
Forms TETRADS
Creates genetic variation
Chromosomes line up in the middle of the cell
Chromosomes move randomly to separate cells
Independent assortment!
Chromosomes are placed into two daughter cells
MEIOSIS I
Meiosis I
Chromosome number is reduced !
Cells are now haploid (n)

12. TETRAD:

13. Chromatids move apart from each other
Chromosomes stay condensed
Cells undergo a second division
Chromosomes line up in middle of cells
Chromatids move apart from each other
One chromatid from each chromosome gets placed in a separate cell
4 genetically different haploid cells are produced
MEIOSIS II

14. Sources of Genetic Variations in Meiosis
Crossing over
In Prophase 1
Homologous chromosomes exchange pieces
Independent Assortment
In Anaphase 1
Chromosomes move randomly to different cells .
Fertilization
“Which sperm gets to the egg first?” – this is random, and generates variations in the offspring.