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Unformatted text preview: PB HLTH C240D/STAT C245D/STAT 246 Spring 2009 Assignment #1: Solutions Due: Tuesday, February 3rd, in class There are three main parts to this assignment. The first part concerns basic Mendelian genetic analysis; the second involves exploring biological WWW re- sources at the National Center for Biotechnology Information (NCBI); the third consists of installing R and Bioconductor software on your own computer. Part I. Mendelian Genetic Analysis Question 1. Mendel. Read Mendels (1866) paper ( www.mendelweb.org ). Question 2. Albinism. (Griffiths et al., 1996, Ex. 10, p. 48) Suppose that a husband and wife are both heterozygous for a recessive gene for albinism. If they have dizygotic (two-egg) twins, what is the probability that both twins have the same phenotype for pigmentation? Solution. Let D and d denote the disease and normal alleles, respectively. Pr(Same phenotype | Parents Dd Dd ) = Pr(Both affected | Parents Dd Dd ) + Pr(Both unaffected | Parents Dd Dd ) = Pr(Both DD | Parents Dd Dd ) + Pr(Both either Dd or dd | Parents Dd Dd ) = 1 4 2 + 3 4 2 = 5 8 = 0 . 625 . u t Question 3. Tay-Sachs disease. (Griffiths et al., 1996, Ex. 16, p. 49) Tay-Sachs disease, or infantile amaurotic idiocy, is a rare human disease in which toxic substances accumulate in nerve cells. The recessive allele responsible for the disease is inherited in a simple Mendelian manner. A woman is planning to Sandrine Dudoit Assignment #1 marry her first cousin, but the couple discovers that their shared grandfathers sister died in infancy of Tay-Sachs disease. You may assume that the grand- fathers sister is the only affected individual in the family and that individuals marrying into the family do not carry the rare disease allele. a) Draw the relevant parts of the pedigree and infer genotypes. b) What is the probability that the cousins first child has Tay-Sachs disease? Solution. a) Let D and d denote the disease and normal alleles, respectively. b) For the first child to be affected, the cousins grandfather must be a het- erozygous carrier (2 / 3 probability, given his unaffected phenotype) and must transmit the disease allele D to both of his children (1 / 2 1 / 2 prob- ability). These children must pass the D allele to both cousins (1...
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This note was uploaded on 03/14/2010 for the course C 240D, C24 taught by Professor S.dudoit during the Spring '09 term at University of California, Berkeley.
- Spring '09