1. Phenotypic Expression: *Penetrance *Expressivity Gene expression often governed by genotype and environment Example: if 9/10 of individuals carrying an allele express the trait, the trait is said to be 90% penetrant *Onset of genetic expression *Temperature

2. Chapter 5: Sex Determination Life cycles and reproductive modes *Asexual reproduction *Primary sexual differentiation *Secondary sexual differentiation *Unisexual, dioecious and gonochoric *Bisexual, monoecious and hermaphroditic *Alternation of generations *Sexual reproduction Some additional terms:

3. Chlamydomonas

4. Maize (Zea mays)

5. Mutants of Maize tassel seed (ts) silkless (sk) barren stalk (ba)

6. Caenorhabditis elegans (C. elegans)

7. Review: Sexual Differentiation Life cycles and reproductive modes *Asexual reproduction –C.elegans hermaphrodite vegetative Chlamydomonas *Alternation in cycles -Chlamydomonas Maize *Sexual reproduction – Chlamydomonas C. elegans Maize Humans

8. X and Y Chromosomes: Early Studies 1906 Edmund B. Wilson and Protenor

9. X and Y Chromosomes: Early Studies Wilson and Lygaeus

10. X and Y Chromosomes: Early Studies Terms: Homogametic sex Heterogametic sex *The male is not always the heterogametic sex… Examples: Moths, butterflies, most birds, some fish, reptiles, amphibians, at least one species of plants

11. Chromosome Composition in Humans Karyotype XX XY

12. The Y Chromosome Pseudoautosomal regions (PAR) NRY Testis Determining Factor (TDF) *SRY – Sex determining region Is the Y chromosome a “genetic wasteland”? *Housekeeping genes *Testis development and function

13. SKALETSKY, et al. (2003) The male-specific region of the human Y chromosome is a mosaic of discrete sequence classes. Nature 423, 825 - 837 The Y Chromosome