Questions 3-4 are based on the information below: A student working in a genetic
ID: 203603 • Letter: Q
Question
Questions 3-4 are based on the information below: A student working in a genetics lab was given the task of studying a new Drosophila mutation called white. In the time allotted, they were only able to perform the crosses shown below. NOTE: W refers to the white phenotype and + refers to the wild ope phenotype A wt female was crossed with a white male. Results of the cross: Offspring Ratio 1.098 1.000 1.098 1.121 Phenotype Number Female:+ 246 Male: + Female: W 246 Male: W 251 Total 0.2544 0.2316 0.2544 0.2596 224 967 Next, starting with new flies (not Fls), a white female was crossed with a wt male. Results of the cross: Offspring Female: +251 238 Female: W 240 Male: W 260 989 PhenotypeNumber ProportionRatio 1.055 1.000 1.008 1.092 0.2538 0.2406 0.2427 0.2629 Male: t Total Next, starting with new flies (not Fls), a white female was crossed with a white male. Results of the cross: Offspring Phenotype Number Proportion Ratio Female: + 157 Male: + Female: W 320 Male: W 318 Total 0.1637 0.1710 0.3337 0.3316 1.000 1.045 2.038 2.025 164 959 3) What is the genetic basis for the white mutation? Circle all that are true. a) white is dominant to the wild-type allele b) white is an X-linked allele c) white is a lethal allele 4) Using Drosophila nomenclature, which symbols correctly represent the white and wild-type alleles for this gene? a) W: white; W: wild-type b) W: white; W": wild-type c) w : white; w: wild-type d) w: white; w : wild-typeExplanation / Answer
3. in this case clearly indicates that the mutation is C). white is a lethal allele because , if it is X linked than all the male mambers that have one X chromosmes must be white, which is not possible, if it is autosomal dominant, that every time a progeny of male of female which contain only one dominant allele for white will be white, which is also not possible as per the table.
4. d) w: white and w+ for wild type
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