Set up for Sordaria Activity

1.  I gave the answers to the homework document on gene linkage from Thursday.
2.  I announced a TEST for FRIDAY on Chapters 14 and 15.
3.  I assigned the HOMEWORK - read about X-inactivation on p. 284 and then read Ch. 15.4.
4.  We discussed X-inactivation

• X-inactivation is responsible for dosage compensation (the reason why males and females function basically the same even though females have twice as many X-chromosome genes)
• The inactivated X is called a Barr Body and can be detected as a black dot when seen through a microscope.
• X-inactivation happens early in embryonic development.  50% of the cells should shut down the maternal X and 50% the paternal X.  All cells created through mitosis from these will shut down the same X chromosome.
• Inactivation is accomplished through methylation.
• A small region, that has a homologue to a section of the Y-chromosome, remains active.

5.  We discussed Sordaria (fungus) and how it is used as a model organism to study crossover.  Go to the following link to remind yourself of what we learned today.  http://www.phschool.com/science/biology_place/labbench/lab3/concepts2.html
6.  After I presented the information students wrote explanations in their own words into their lab book under the title Lab 3: Crossover.