Lec3JCL_W2009 - Bio 305 Lecture 3: Sex-linked inheritance,...

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Bio 305 Lecture 3: Sex-linked inheritance, pedigrees and proof of the chromosomal theory Jan 13, 2009 Dr. Long Required reading: Pre-lecture reading below, including specified book pages Optional further reading: Chapter 2 (p. 57-75) Relevant end of chapter problems: Chapter 2 (30, 37 - 52, 54, 56, 57) Relevant problems in the course pack: 6-11 Vocabulary: (also see genetic notation summary) affected individual autosome Bayes’ theorem carrier complement of an event conditional probability dimorphism haploid chromosome set ( n ) hemizygous heterogametic homogametic nondisjunction pedigree analysis ploidy polymorphism posterior probability prior probability sex chromosomes (X chromosome, Y chromosome) sex-linkage total probability law X-linkage Y-linkage Learning Goals: Based on the reading and lecture material from lecture 3, you need to be able to: 1. Describe the similarities and differences between human X and Y chromosomes as well as the evolutionary origin of the Y chromosome. 2. Draw the segregation of sex chromosomes during mitosis and meiosis. 3. Describe features of chromosome number, sex chromosomes and sex determination that are the same and different among species. 4. Explain how genes were first shown to be located on chromosomes. 5. Predict inheritance patterns for X-linked genes. 6. Use pedigree data to infer the most likely mode of inheritance for a trait and to predict the probability of additional offspring inheriting the trait. 7. Translate descriptions of phenotypes into appropriate genotypic notation in pedigrees and in standard crosses. 8. Compute posterior probabilities using Bayes' theorem. 9. Calculate conditional probabilities, when appropriate. Lecture 3 1
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Pre-lecture reading Lecture 3, Jan 13, 2009 3.1 Why do so many organisms have two distinct sexes? Sexual reproduction helps maintain genetic diversity within populations of a species by bringing together different alleles at each generation. This genetic variation produces phenotypic variation that makes individuals differentially suited to their environments. Natural selection, along with other evolutionary processes, causes organisms to evolve. 3.2 Sex chromosomes and chromosome number: "Most animals and many plants show sexual dimorphism; in other words, individuals are either male or female. In most of these cases, sex is determined by a special pair of chromosomes called sex chromosomes . Let's look at humans as an example. Human body cells have 46 chromosomes: 22 homologous pairs of autosomes plus 2 sex chromosomes. Females have a pair of identical sex chromosomes called the X chromosomes . Males have a non-identical pair, consisting of one X and one Y. The Y chromosome is considerably shorter than the X. " (from Griffiths et al. p. 61) Different species have different types of sex-chromosomes and different combinations that trigger male and female development. Most common is the XY system (e.g. humans, Drosophila ) in which males have two different sex chromosomes (
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This note was uploaded on 10/24/2009 for the course BIO 305 taught by Professor Wittkopp/csankovzski during the Winter '08 term at University of Michigan.

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Lec3JCL_W2009 - Bio 305 Lecture 3: Sex-linked inheritance,...

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