BIO 202 HW 1

# BIO 202 HW 1 - BIOL 202 HOMEWORK#1 Student's Name_KEY...

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BIOL 202 Student’s Name_________________________ KEY__ HOMEWORK #1 Section number and TA’s name:_________________ DUE: Jan 31/Feb1 in your discussion section. IMPORTANT: Please type (not hand-write) your answers onto the question sheet itself (this sheet). Please highlight or otherwise indicate the parts that you have typed with underlining or bold ing. If additional working is required, it will be specifically stated so in the question, and whether the working should be shown on the answer sheet or a supplemental sheet will also be stated. 1. In Rich’s office there is a small colony of true-breeding dust bunnies. All his dust bunnies are grey (they’re English ones !) and they also have coarse hair. By contrast, Kelly’s office has dust bunnies which are brown and have soft hair. When we mated one of Rich’s coarse grey bunnies from home to one of Kelly’s soft brown bunnies, all 17 offspring were soft and brown. Clearly dust bunnies mate like real bunnies ! When these F1 bunnies were allowed to mate amongst themselves, we got a total of 923 with brown fur and soft hair, and 317 with grey fur and coarse hair. (2 points) a. What is the most likely phenotypic ratio you observe in the F2 ? EXPLANATION 923 brown soft + 317 grey coarse =1240 total offspring 923 / 1240 = 74.4% brown soft (which is approximately 75%) 317 / 1240 = 25.6% grey coarse (which is approximately 25%) ANSWER (0.5 pt) 3 brown soft : 1 grey coarse b. Based upon this ratio, how many genes control these characteristics ? ANSWER (0.5 pt) One gene controls both color and roughness. EXPLANATION Although we see color and roughness as 2 different traits, when we look at the grandchildren (F2 generation), we see only 2 types. If we assume independent assortment of alleles, this means that both traits are caused by the same gene (an example of pleiotropy). If the 2 traits were caused by 2 different genes, we would expect independent assortment to have produced 4 types of F2 grandkids and those types to occur in a 9:3:3:1 ratio.

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c. Which characteristics are dominant and which are recessive ? ANSWER (0.5 pt) Brown soft is dominant and grey coarse is recessive. EXPLANATION We can determine this by looking at the phenotypic ratio of the F2 generation. The phenotype that occurs in ¾ of the individuals is the dominant characteristic and the other is the recessive.
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