TRUE OR FALSE? A Drosophila fly carries a trait that results in spotted wings. This true-breeding spotted- wing fly is crossed to a true-breeding wild-type fly resulting in progeny that all have spotted wings. When the F1 progeny are selfed, the F2 progeny exhibit a 3:1 ratio of spotted-wing to wild-type wing flies. In order to perform a testcross with an F2 spotted- wing fly, you would cross it to another F2 spotted-wing fly.
False. The phenotypic results of the F1 and F2 progeny are consistent with spotted-wing being a dominant allele (designate S) to wild-type (designate S+). The appropriate fly for a testcross with the F2 spotted-wing fly (presumably to determine whether the spotted-wing fly is a homozygote or heterozygote), we would need to cross it to the homozygous recessive allele, which in this case is S+S+ (homozygous wild type).
4. What aspect of chromosome behavior most clearly accounts for Mendel's Principle of Segregation?
A. Movement of sister chromatids to opposite poles at anaphase II of meiosis.
B. Movement of homologous chromosomes to opposite poles at anaphase I of meiosis. (each centrosome attaches via kinetochore microtubules to one or the other chromosome homolog)
C. Crossing over between homologous chromosomes during prophase I of meiosis.
D. Replication of chromosomes prior to meiosis.
E. Independent alignment of different homologous pairs on the metaphase I spindle.
B. Movement of homologous chromosomes to opposite poles at anaphase I of meiosis. (each centrosome attaches via kinetochore microtubules to one or the other chromosome homolog)
(D would be the answer if the question were about the Principle of Independent Assortment)