C2005/F2401 '08 -- Outline for Lecture 20

Last posted/updated 11/24/08 03:15 PM

I. Wrap up of Karyotypes -- Aneuploidy (this section skipped in lecture 19)

II. Steps of Meiosis (Handout 19A)

III. Life Cycles  (Handout 20A -- top)

IV. Nondisjunction  -- how mistakes in meiosis cause aneuploidy  (Handout 20A -- bottom)

V. Inactive X's and Barr Bodies. Why extra X's are tolerated but extra autosomes are not.

     A. Lyon Hypothesis -- inactivation of "extra" X chromosomes

    B. Barr bodies -- seeing the inactive X

    C. How X inactivation was detected  -- orange and black cats; Introduction to genetic terminology:

        heterozygous, homozygous, loci, alleles

    D. When & how Barr body forms

VI. Patterns of Inheritance for Sex Linked Genes -- For example, cat coat color -- orange vs black. (Handout 20B, top.)

    A. What gametes are formed?

    B. What Zygotes are formed?

    C. What do zygotes look like? How does genotype determine phenotype in this case

Next time: What is the Pattern of Inheritance for genes on autosomes? (Handout 20B, bottom.)