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Unformatted text preview: 1 Sept 24, 2009 Today: Modifications and Extensions of Mendels Basic Principles (to be continued in Sept 29 lecture) Quiz 1 next week: 15 minutes in recitation Exam 1 in two weeks (Oct 8 th ): multiple choice; short answer/problem Check Sakai Resources for last years exams and quizzes Section 7 recitation will now meet in ARC 204. TA Larry Kramer. Mid-course online evaluations: anonymous Sex-linked characteristics X-linked inheritance Y-linked Disorders Morgans observation Pure breeding Red eye female White eye male PO F1 All red eye progeny (except 3 white-eyed males among 1237 progeny) F2 All red eye female 1/2 red eye male 1/2 white eye male Not expected result for a simple recessive trait, which should appear in what fraction?? of both male and female F2 offspring. 2 Equalizes the amount of protein produced by X-linked genes in the two sexes. In male flies, doubled X activity. In C. elegans worms, X activity is halved on both Xs. In placental mammals, one X is inactivated in females. A Barr body is an inactivated X chromosome . Dosage compensation XX cell XY cell X-linked recessive: Color Blindness X-linked dominant: uncommon hypophosphatemia: vitamin D rickets hypertrichosis: excess body and facial hair Y-linked SRY and maleness No convincing cases of nonsexual phenotypic variants associated with Y. Hairy ear rims possible, but disputed. Tangent: Autosomal aneuploids Trisomy 21: Down syndrome Chromosome 21 has fewer genes than on any autosome, with only about 230 genes of a total of 20,000 to 25,000 for the entire human genome 1 in 700, incidence increases with maternal age Primary Down syndrome (92%): three full copies of chromosome 21....
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