2. Asexual vs. Sexual Reproduction Asexual: -single individual is sole parent and passes ALL genes to offspring -offspring are genetically identical to parent’s -results in a clone…rarely a genetic difference will occur as a result of a mutation which can lead to cancer

3. Sexual Reproduction -two parents give rise to offspring -each person passes on half of its genes to its offspring -offspring have a unique combination of genes inherited from both parents -results in greater genetic variation; offspring vary genetically from their siblings and parents

4. Meiosis creates genetic variation -Recall mitosis produces two daughter cells genetically identical to parent and to each other. Meiosis will produce FOUR daughter cells genetically different from parent and each other.

5. Sexual Reproduction Varies in Meiosis By… -Independent assortment- random alignment and each chromosome orients independently of other pairs -Random Fertilization- An egg cell is 1 of 8 million possibilities and a sperm cell is also 1 of 8 million possibilities…thus, a zygote can have 1 of 64 trillion different combinations -Crossing Over- (we’ll get to this at the end)

6. Crossing Over

8. Crossing Over Cont… -occurs when homologous portions of two nonsister chromosomes trade places -produces chromosomes that contain genes from both parents -in humans, average of 2-3 crossovers per chromosome pair

9. Intro Sex Cell Division: Meiosis Meiosis is cell division of sex cells to form egg and sperm

10. Meiosis vocabulary 1. Meiosis - a two stage cell division in which the chromosome number is halved. It forms four different gametes (sex cells) Meiosis I and Meiosis II 2. Gamete - the reproductive cell (egg or sperm)

11. Meiosis vocabulary cont. 3. Haploid – “half” (as in when the human cell has only 23 single chromosomes (gamete cells) (n=23) 4.Diploid – “two” (as in when the human cell has 23 pairs of chromosomes (2n =46) 5.“homologous” chromosomes- same size, centromere pairing, and staining pattern

13. Vocab Cont… 6. somatic cell- any cell other than sperm or egg 7. autosome- a chromosome (recall: threadlike structure in eukaryote made of DNA + protein) that is NOT a sex chromosome 8. zygote- diploid cell that results from union of two haploid gametes

15. Meiosis Steps 1. Pre-Meiosis - Interphase 2. Meiosis I - Prophase I - Metaphase I - Anaphase I - Telophase I 3. Meiosis II - Prophase II - Metaphase II - Anaphase II - Telophase II 4. Post-Meiosis - Cytokinesis

16. Why is Meiosis important? All gametes must be haploid (n = 23 chromosomes) Egg (n=23) + Sperm (n=23) offspring (2n=46) normal

17. Pre-Meiosis: Interphase 46 chromosomes ----> 92 chromosomes diploid 1. copy Chromosomes 2. copy centriole

18. No Interphase between Meiosis I and Meiosis II

19. Chromosome Vocab SYNAPSIS

20. Chiasma

21. In males, cytokinesis makes four equal cells that develop heads and tails = sperm Cytokinesis In females, cytokinesis is unequal; one cell gets most of the cytoplasm to become the mature egg, while the other three (called polar bodies) are not involved.

23. Cytokinesis In Males, cytokinesis makes four equal cells that develop heads and tails = sperm In females, cytokinesis is unequal; one cell gets most of the cytoplasm to become the mature egg, the other three (polar bodies) usually die

26. Variety of Sexual Life Cycles -in animals, gametes are the only haploid cells -in fungi, the organism in normally haploid and the only diploid stage is the zygote (meiosis follows immediately) -plants (and some algae)- called “alternation of generations”… (see following diagram)

28. Ch 14 WarmUp 1. What is the difference between an allele and a gene? 2. Briefly define the following terms: a. homozygous b. heterozygous c. phenotype d. Genotype 3. What is the difference between pleiotrophy and epistasis? 4. Describe the following disorders: Cystic Fibrosis, Tay- Sachs, Sickle Cell Anemia, Achondroplasia, and Huntington’s disease.