3. (30 points total) Feather color in parakeets is produced by the blending of p
ID: 3165030 • Letter: 3
Question
3. (30 points total) Feather color in parakeets is produced by the blending of pigments produced bv two biosvnthetic pathways shown below. Four independently assorting genes (A, B, C, and D) code for the enzymes that catalyze the separate steps of the pathways. At each locus, the wild-type dominant alleles, e.g. A, code for functional enzymes, and recessive alleles, e.g. AT, correspond to loss of function. Red, yellow, and blue plumage results from production of one pigment in the absence of others. Purple and green feathers are due to the combination of two pigments, and white is the absence of pigment production colorless precursorI red pigment II» vellow pigment III enzyme A enzyme B colorless precursorX colorless intermediate Y y blue pigment Z enzyme (C enzyme ID a. (5 points) What are the possible genotypes of a pure-breeding (homozygous) purple parakeet? b. (5 points) What are the possible genotypes of a pure-breeding yellow parakeet? c. (10 points) What are the phenotypic and genotypic predictions for the offspring from the following cross of a green with a blue? d. (10 points) If the Fi birds identified in part (c) are mated at random, what genotypic and phenotvpic ratios do vou predict for the F2 generation?Explanation / Answer
a)PaPb×PaPb
F1-2 purple 1 blue and 1 red plummage.PaPa,PbPb,PaPbPaPb where Pa is allele for one color say red and On for blue.
b)PyPy×PyPy gives all yellow plummage in F1 generation provided yellow is dominant. IF THE genotype is Pypy×Pypy then ratio becomes 3:1 yellow: wwhite.
c)frequency of A+A- = 2 , frequency A+B- =2 ,A+C+ =2, A+D+=2, B+B-, =2 ,B+C+ =2, B+D+=2 ,C+D+ =2. Numbers give the frequency of individual genotypes.
D)For ex: If A+B- are mated with B+B- the genotype in F1 generation will be A+B+, 2 B+B-,B-B-. Thus one will get 1 pure dominant phenotype, 2 dominant but with both alleles and one recessive if A-B- genotypes are mated else entire pool will be a mixed one and may get an intermediate phenotype.
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