Drosophila researchers have collected many strainsthat carry a single recombinant P element containing awild-type white gene (a P[w+] transgene) inserted intoa known genomic location. These strains can be used tomap the location of any mutant gene in the fly genome.Investigators performed a testcross to map arecessive mutation rough (ro), which causes rougheyes, relative to a P[w+] element on chromosome 3.Females heterozygous for the P[w+] on one chromosome 3 and a ro− mutation on the other, homologouschromosome 3 were crossed to ro−/ro− males, and theprogeny in the following list were obtained. In boththe parents and the progeny, the endogenous whitegene is nonfunctional—the flies have red eyes onlyif they contain the P[w+] transgene.145 red, smooth (wild-type) eyes152 white, rough eyes2 white, smooth eyes1 red, rough eyesa. Are ro and the P[w+] linked? If so, how many mapunits separate them?b. The data in part (a) do not indicate on which sideof the P[w+] (toward the centromere or telomere)the ro gene is located. How could the experimentbe modified to reveal that information?c. Suppose you map the ro mutation to a genomic region between two different P[w+] elements that are5000 bp apart. Describe some experimental approaches that would allow you to identify the rogene at the molecular level.d. How could you use the DNA sequence of the rogene to determine the function of the protein itencodes?
Drosophila researchers have collected many strains
that carry a single recombinant P element containing a
wild-type white gene (a P[w+] transgene) inserted into
a known genomic location. These strains can be used to
map the location of any mutant gene in the fly genome.
Investigators performed a testcross to map a
recessive mutation rough (ro), which causes rough
eyes, relative to a P[w+] element on chromosome 3.
Females heterozygous for the P[w+] on one chromosome 3 and a ro− mutation on the other, homologous
chromosome 3 were crossed to ro−/ro− males, and the
progeny in the following list were obtained. In both
the parents and the progeny, the endogenous whitegene is nonfunctional—the flies have red eyes only
if they contain the P[w+] transgene.
145 red, smooth (wild-type) eyes
152 white, rough eyes
2 white, smooth eyes
1 red, rough eyes
a. Are ro and the P[w+] linked? If so, how many map
units separate them?
b. The data in part (a) do not indicate on which side
of the P[w+] (toward the centromere or telomere)
the ro gene is located. How could the experiment
be modified to reveal that information?
c. Suppose you map the ro mutation to a genomic region between two different P[w+] elements that are
5000 bp apart. Describe some experimental approaches that would allow you to identify the ro
gene at the molecular level.
d. How could you use the DNA sequence of the ro
gene to determine the function of the protein it
encodes?
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