1st+day+PS+Key - Bio 137B Human and Eukaryotic Genetics 1st...

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Bio 137B Human and Eukaryotic Genetics 1st day in class exam J.L.Marsh Find 2 people who did not go to your highschool: Name_____________________________ Highschool&City ____________________ Name_____________________________ Highschool&City ____________________ 1] What is Mendel's first law? It is called the principle of _____________________________ [a] What does it say? [b] If a father, who is a carrier of a recessive trait, marries a normal woman, what proportion of the offspring are expected to be affected vs. carriers vs. normal (i.e. not affected; non carrier)? Draw a Punnett square for this mating. Answ : Principle of equal segregation. Most organisms are diploid Homologous chromosomes which carry the different alleles of genes, will segregate equally to the gametes. In the past, some people answered that the first law says alleles segregate independently !! If alleles were independent, THEN sometimes one would expect to get both alleles or none in a gamete. Mendel's first law of equal segregation is the genetic manifestation of the cell biological observation that homologous chromosomes separte (disjoin) during Meiosis. The most frequent cause of human disease by far, is failure of this process (e.g. downs patients). b]If G = any normal gene and g = the recessive form of that normal gene, then the father must be Gg. The mother is normal and we assume GG since we are given no information to make us suspect anything else but we note that this is an assumption. Why do we make this assumption? Because for any given mutation, most people in the population are NOT carriers . If any evidence comes along to challenge our assumption about this particular woman, we will have to change our thinking. However, making this assumption, the mating between these two will all be Gg x GG --> Gg:GG = 1:1 or 50:50 carrier to non-carrier
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1st+day+PS+Key - Bio 137B Human and Eukaryotic Genetics 1st...

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