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

2. 1. sex cells (gametes: egg and sperm)
SEXUAL Reproduction
Requires:
1. sex cells (gametes: egg and sperm)
2. fertilization (when gametes combine)
GENETIC DIVERSITY:
produces a greater chance of variation within a species than asexual reproduction
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. MITOSIS
Sexual reproduction results in offspring that are genetically different from the parent organisms. Needs 2 parents. MEIOSIS

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
IN ALL CELLS: Chromosome pairs
1-22 are autosomes. Chromosomes 23 are
Sex-chromosomes
X and Y, determine gender in mammals.
XX = female
XY = male

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
MEIOSIS
CELLS
SOMATIC
SEX CELLS (GAMETES
NO. OF DAUGHTER CELLS 2 4
NO. OF CHROMOSOMES IN EACH DAUGHTER CELL
DIPLOID (PAIR)
HAPLOID (HALF)
DIVERSITY
GENETICALLY IDENTICAL DAUGHTER CELLS
GENETICALLY DIFFERENT DAUGHTER CELLS
WHEN
THROUGHOUT ORGANISMS’ LIFETIME
ONLY CERTAIN TIMES IN ORGANISMS’ LIFE CYCLE
TYPE OF REPRODUCTION
ASEXUAL
SEXUAL

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

10. Meiosis I MEIOSIS I Chromosomes condense
Crossing over occurs during synapsis (when chromosomes pair up to exchange pieces)
Chromosomes exchange pieces
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)

11. MEIOSIS 1 IMPORTANT EVENTS:
homologous chromosomes
sister
chromatids
MEIOSIS I: PMAT 1
1. crossing over occurs during synapsis and the formation of tetrads (Prophase I)
2. pairs of homologous chromosomes separate (Anaphase I)
Synapsis: pairing of homologous chromosomes forming a TETRAD (group of 4 chromatids)

12. 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

13. MEIOSIS 2 IMPORTANT EVENTS:
1. SISTER CHROMATIDES separate during ANAPHASE 2
homologous chromosomes
sister
chromatids

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.