09.13.11 - Lecture 3. Sex linkage and pedigree analysis...

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Lecture 3. Sex linkage and pedigree analysis Readings: Chapter 2: 50-65
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The solution to understanding the laws of heredity were found by finding and studying mutations wild type vs. mutant loss-of-function mutation (e.g. albinism; tyrosinase mutation) gain-of-function mutation (e.g. lactose tolerance; lactase persistence allele) neutral mutation (non-coding, silent mutation)
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Clicker Question 1: The allele for lactase persistence would best be described as a: a. dominant mutation b. recessive mutation c. partially dominant mutation d. wild type allele e. codominant with wild type
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Frequency of lactase persistence allele environmentally variable polymorphism Itan et al. BMC Evolutionary Biology 2010 10:36
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Concepts 1. In organisms with sex chromosomes, the heterogametic sex is hemizygous and contains only a single copy (homologue) of sex linked genes. 2. Genes on the sex chromosomes show gender specific segregation patterns. 3. In organisms which cannot be manipulated in the lab, the inheritance of traits can be analyzed by use of pedigrees.
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Sex linkage was shown to be the first proof of the chromosomal theory of inheritance : Specifically- mutations effecting traits other than sex determination were shown to reside on the sex chromosomes. In the next slides we will: 1. Standardize our nomenclature for genes and loci 2. Discuss the product law of probability 3. Discuss the basic sex chromosome system in bugs and mammals 4. Use this to predict the expect proportion of offspring of a given sex with a mutant phenotype.
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Symbols: The initial letter of the name of a recessive trait, lowercased and italicized, denotes the recessive allele, and the same letter in uppercase refers to the dominant allele. G g Wild-type=+ /- mutant usually expressed as (-) mutant= initials of the name of the mutant trait (uppercase for dominant and lowercase for recessive trait) : ads, Ubx Dominant phenotype (genotype unknown):G (with underscore) examples: +/+ ; e + /e; +/e ; e / e . e stands for ebony body color. Human Mouse Gene BRCA1 Brca1 Protein BRCA1 Brca1 I. Gene/locus nomenclature
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II. Product “AND” Rule The probability that two INDEPENDENT events will BOTH occur is the PRODUCT of the probability of each occurring.
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09.13.11 - Lecture 3. Sex linkage and pedigree analysis...

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