1. Meiosis and Sexual Life Cycles
Chapter 13
Unit 5

2. Types of Reproduction Produces clones (genetically identical)
ASEXUAL
SEXUAL
Produces clones (genetically identical)
Single parent
Little variation in population - only through mutations
Fast and energy efficient
Eg. budding, binary fission
Meiosis produces gametes (sex cells)
2 parents: male/female
Lots of variation/diversity
Slower and energy consumptive
Eg. humans, trees

3. Chromosomes Somatic (body) cell: 2n = 46 chromosomes
Each pair of homologous chromosomes includes 1 chromosome from each parent
Autosomes: 22 pairs of chromosomes that do not determine sex
Sex chromosomes: X and Y
Females: XX Males: XY
Gametes (n=23): 22 autosomes + 1 sex
Egg: 22 + X Sperm: 22 + X or Y

4. Homologous Chromosomes in a Somatic Cell

5. Karyotype Picture of an organisms chromosomes
Arranged from largest to smallest
Used to detect genetic abnormalities

6. Male or female?

7. Meiosis Reduction division Evolved from mitosis
Similar stages and machinery, but different processes
Results in 4 genetically different haploid cells
Makes gametes

8. Meiosis I (1st division)
Interphase: chromosomes replicated
Prophase I:
Synapsis: homologous chromosomes pair up
Tetrad = 4 sister chromatids
Crossing over at the chiasmata
Metaphase I: Tetrads line up
Anaphase I:
Pairs of homologous chromosomes separate
Telophase I & Cytokinesis:
Haploid set of chromosomes in each cell
Each chromosome = 2 sister chromatids

10. Meiosis II (2nd division)
Prophase II:
No interphase
No crossing over
Spindle forms
Metaphase II:
Chromosomes line up
Anaphase II:
Sister chromatids separate
Telophase II:
4 haploid cells
Nuclei reappear
Each daughter cell genetically unique

11. Sources of Genetic Variation
Independent assortment:
random orientation of homologous pairs in Metaphase I
Crossing over
Exchange genetic material
Random fusion of gametes during fertilization

12. Mitosis vs. Meiosis Mitosis 1 division Meiosis 2 divisions
daughter cells genetically identical to parent cell
produces 2 cells
2n  2n
produces cells for growth & repair
no crossing over
Meiosis
2 divisions
daughter cells genetically different from parent
produces 4 cells
2n  1n
produces gametes
crossing over