Genetics Problem Set with solutions

Genetics Problem Set with solutions - BIO311D Spring 2011...

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BIO311D Spring 2011 ANSWER KEY Moon The “more fun with genetics” problem set : These are some examples of problems that may appear on the exam. See if you can work these without looking at the answers. I’ll post the detailed answers separately. If you can do these problems, you’ll be in good shape for the exam. 1. You’re given a fly ( Drosophila ) with Purple eyes, a dominant trait (P) to White eyes (p). How would you determine if the fly was PP or Pp? Cross P- fly to a homozygous recessive fly with white eyes (pp) – this is called a testcross. The phenotypic ratio of the offspring will tell you the genotype of your fly. A 1 Purple eye :1 White eye ratio in the offspring means the fly was Pp. If all the offspring flies are Purple eyed, your fly was PP. 2. Two black guinea pigs were mated and over several years produced 29 black and 9 white offspring. Explain these results, giving the genotypes of the parents and progeny. The offspring ratio is close to 3:1, which is what you would expect if both the parents were heterozygous. (TIP: do a Punnett square Bb X Bb and take a look at the phenotypic ratio of offspring). The parent guinea pigs are each Bb, the offspring are 29 black (BB and Bb, about 10 BB and 20 Bb, give or take) and 9 white, which have to be bb. The numbers don’t have to be perfectly 3:1 – this is a small population size, so there will be some variation. 3. Achondroplasia is a form of dwarfism caused by a mutation in a single gene. Two achondroplastic dwarfs marry and have a dwarf child; later, they have a second child who is normal. a. Is Achondroplasia recessive or dominant? Of course, you could remember this from your textbook and lecture, but realize that it must be dominant, and the parents must be heterozygous, because the parents are dwarfs and they had both a normal child and an affected child. (Is it inappropriate to call them dwarves? I see ‘dwarfs’ in the textbook. Hm.) b. What are the genotypes of the two parents? Heterozygous, see above c. What is the probability that their next child will be normal? ¼ (do a Punnett square) d. What is the probability that their next child will be a dwarf? ¾ 1
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BIO311D Spring 2011 ANSWER KEY Moon 4. (A bit more challenging) Duchene’s muscular dystrophy is X-linked and usually affects males. Victims of the disease become progressive weaker, starting early in life. Karen’s brother has muscular dystrophy.
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This note was uploaded on 07/25/2011 for the course BIO 311 D taught by Professor Zhao during the Spring '08 term at University of Texas.

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Genetics Problem Set with solutions - BIO311D Spring 2011...

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