8) There are three mutations on the second chromosome of Drosophila (actually th

Question

8) There are three mutations on the second chromosome of Drosophila (actually there are several hundred, but we will only concern ourselves with three), Speck (Sp), fuzzy (fy), and cup (c). Two homozygous lines of flies were crossed and heterozygous female progeny were test -crossed to males homozygous for all the recessive alleles. The following phenotypes were observed among the test -cross progeny. Wild type .................. 1 Speck, fuzzy, cup ......0 cup .......................... 21 Speck, fuzzy ............ 18 Speck, cup ...............95 fuzzy ....................... 84 Speck .................... 379 fuzzy, cup ..............402 On the line tc the right of each type indicate which chromosome those flies must have gotten from the heterozygous parent. The first one is done for you. What were the phenotypes of the original homozygous parents? Draw a map of this region of the second chromosome indicating the order of the three loci and the map distances between them. Calculate the coefficient of coincidence.

Explanation / Answer

A frameshift mutation is a genetic mutation caused by a deletion or insertion in a DNA sequence that shifts the way the sequence is read. A DNA sequence is a chain of many smaller molecules called nucleotides. DNA (or RNA) nucleotide sequences are read three nucleotides at a time in units called codons, and each codon corresponds to a specific amino acid or stop signal. During translation, the sequence of codons is read in order from the nucleotide sequence to synthesize a chain of amino acids and form a protein. Frameshift mutations arise when the normal sequence of codons is disrupted by the insertion or deletion of one or more nucleotides, provided that the number of nucleotides added or removed is not a multiple of three. For instance, if just one nucleotide is deleted from the sequence, then all of the codons including and after the mutation will have a disrupted reading frame. This can result in the incorporation of many incorrect amino acids into the protein. In contrast, if three nucleotides are inserted or deleted, there will be no shift in the codon reading frame; however, there will be either one extra or one missing amino acid in the final protein. Therefore, frameshift mutations result in abnormal protein products with an incorrect amino acid sequence that can be either longer or shorter than the normal protein.

Related Questions

Navigate

• Browse (All)
• Browse 8
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.