1. Reproduction and Meiosis

2. Reproduction Reproduction—the process of producing offspring
Asexual—one parent, offspring are genetically identical to parent
Budding, fission, fragmentation, parthenogenesis
Sexual—two parents, offspring genetically different from parents
Parents produce gametes
Females=egg
Males=sperm
Two gametes combine=fertilization; produces first cell called the zygote
Offspring will have traits of both parents

3. Homologous Chromosomes
Each species has a characteristic number of chromosomes
Humans=46; dogs=78; fruit flies=8
Chromosomes come in pairs—homologous chromosomes
Chromosomes with the same size, shape, and carry the codes for the same genes
Each chromosome in a homologous pair comes from one of the parents
In humans, 23 chromosomes come from mom and 23 from dad

4. Meiosis
Form of cell division that produces 4 daughter cells with half the number of chromosomes as the parent cell
2 distinct stages
Meiosis I
Prophase I, Metaphase I, Anaphase I,
Telophase I
Meiosis II
Prophase II, Metaphase II, Anaphase II,
Telophase II

5. Meiosis I Prophase I Chromosomes condense
Homologous chromosomes pair up
Crossing over
Chromatids exchange genetic material
Increases genetic variability

6. Meiosis I Metaphase I Anaphase I Telophase I
Homologous chromosomes line up along equator of cell
Anaphase I
Homologous chromosomes move apart, pulled by spindle fibers
Telophase I
Cytoplasm divides, resulting in two cells with the same number of chromosomes as parent

7. 4 different haploid cells
Meiosis II
Prophase II
Metaphase II
Telophase II
4 different haploid cells
Anaphase II

8. Results of Meiosis Gametes (egg & sperm) form
Four haploid cells with one copy of each chromosome
One allele of each gene
Different combinations of alleles for different genes along the chromosome

9. Mitosis vs Meiosis Mitosis Meiosis Number of divisions 1 2
Number of daughter cells 4
Genetically identical?
Yes No
Chromosome #
Same as parent
Half of parent
Where
Body cells
Sex cells
When
Throughout life
At sexual maturity
Role
Growth and Repair
Sexual Reproduction

10. Gamete Production
Gametes have half the number of chromosomes of the organism
Sperm (23 chromosomes) + Egg (23 chromosomes) = Human (46 chromosomes)
Diploid (2n)
A cell with two of each chromosome, which are in pairs {FULL set}
Haploid (n)
A cell with only one of each chromosome {half set}

11. Gamete Production: Sperm
Occurs in the testes
Two divisions produce 4 spermatids
Spermatids mature into sperm
Men produce about 250,000,000 sperm per day

12. Gamete Production: Egg
Occurs in the ovaries
Two divisions produce 3 polar bodies that die and 1 egg
Polar bodies die because of unequal division of cytoplasm
Immature egg called oocyte
Starting at puberty, one oocyte matures into an ovum (egg) every 28 days