section15_ak

section15_ak - MIT Department of Biology 7.014 Introductory...

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MIT Department of Biology 7.014 Introductory Biology, Spring 2005 Recitation Section 15 Answer Key April 4-5, 2005 Diploid Genetics and Chromosomal Inheritance A. Diploid Genetics For each set of data below, determine the genotype of the parents in cross 1. Where it applies, indicate which phenotypes are dominant and which are recessive. 1. Mice I a) cross 1: red-eyed mouse ____________ X white-eyed mouse ____________ gives F 1 : all red-eyed cross 2: red-eyed F 1 X red-eyed F 1 gives F 2 : 36 red-eyed 13 white-eyed Cross 1: red eyes X white eyes gives all red eyes – a likely model is that eye color is controlled by one gene that has 2 alleles producing two phenotypes, red and white eyes. The red eyed phenotype is likely dominant. Therefore, choose appropriate symbols (one letter per gene, capital letter for allele with dominant phenotype): •R - red allele. Dominant phenotype of red eyes. •r - white allele. Recessive phenotype of white eyes. Then: Cross 1 is: RR X rr ----> all Rr (all red eyes). Cross 2 is: Rr X Rr ----> 3:1 red:white. The predictions agree with the data. b) cross 1: long-eared mouse ____________ X short-eared mouse ____________ gives F 1 : 12 long-eared 10 short-eared cross 2: long-eared F 1 X long-eared F 1 gives F 2 : 36 long-eared 13 short-eared Cross 1: long ears X short ears gives some long and some short ears – a likely model is that ear length is controlled by one gene with 2 alleles resulting in two phenotypes, long ears and short ears. From this data, we cannot determine which allele has the dominant phenotype. Cross 2: long ears X long ears gives some long and some short ears – a likely model is that long ears is the
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section15_ak - MIT Department of Biology 7.014 Introductory...

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