1. In fruit flies the wild-type eye color is red. A recessive allele (pd) result
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Question
1. In fruit flies the wild-type eye color is red. A recessive allele (pd) results in purple eyes. Another recessive allele (su) of a different gene results in no apparent phenotype in homozygous flies; however, when two dihybrid (pd+/pd;su+/su) flies are crossed, the phenotypic ratio of the progeny is 13:3 (red eyes to purple eyes). How would you interpret this result?
a) The pd allele is a recessive suppressor of the su allele.
b)The su allele is a recessive suppressor of the pd allele.
c) The pd allele is only recessively epistatic.
d)The su allele is lethal.None of the answers is correct.
2. Incomplete dominance is the result of a dose effect by the wild-type allele. Imagine that it takes 3 units of pigment to produce a red flower in peonies. If a peony wild-type allele produces 2 units of pigment and a mutant allele produces no pigment, how many units of pigment will be produced by homozygous wild-type, heterozygous, and homozygous mutant peonies, respectively?
a)4; 2; 0
b) 3; 2; 0
c)2; 4; 0
d)0; 4; 2
e) 0; 1; 0
3. A researcher is studying four genes, A, B, C, and D, in mice. He has bred mice that are homozygous for null mutations in each of these genes, which are denoted as A–/A–, B–/B–, C–/C–, and D–/D–. He determines that A–/A– and D–/D– mice die in utero, but C–/C– and B–/B– mice appear relatively normal. Of A, B, C, and D, which are essential genes?
a) A and C
b) B and C
c)A and D
e)C and D
f) A and B
4. The arginine biosynthetic pathway is as follows: precursor ? ornithine ? citrulline ? arginine. The three arginine mutants of Beadle and Tatum are named arg-1, arg-2, and arg-3. The arg-1 mutant grows with treatment of ornithine, citrulline, or arginine. The wild-type arg-1 gene codes for an enzyme that:
a) converts a precursor molecule to ornithine.
b) converts ornithine to citrulline
c) converts citrulline to arginine.
d) converts arginine to a precursor molecule
e) is active in a different pathway.
Explanation / Answer
1. b)The su allele is a recessive suppressor of the pd allele.
2. A. 4; 2; 0
Wild type alleles 2 units. So homozygous wild type WW = 4
Heterozygous = 2+0 = 2
Mutant homozygous = 0
3. A and D
A and D are essential gene because if we mutated the A and D the mice die in utero. But C and B not have any effect in the mutation.
4. a) converts a precursor molecule to ornithine.
precursor--- ornithine --- citrulline --- arginine.
1 2 3
Three enzymes are involved in conversion pf precursor to arginine. Mutate 1 it not convert to ornithine but we add
in the media it will grow.
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