1. This set of questions deals with genetics clues that suggest proteins a. Why
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1. This set of questions deals with genetics clues that suggest proteins a. Why does a dominant negative phenotype indicate a protein may b. Does a hypermorphic mutation also indicate this? Why or why interact with one another be acting as a homomultimer? not? c. In B1214 you learned about genetic complementation. You have a group of mutant eyeless flies. You do a complementation test with two of these flies, and you find they compliment. What does this mean, and why? (we do not cover this in BI320, so if you do not remember from B1214 or honors bio, you'll have to look it up) d. If you have two mutant proteins that show a pseudo-reversion phenotype (second site suppressor) there is a strong possibility that the two proteins interact. Explain in your own words why a mutation in one protein can rescue (at least partially) the phenotype cause by a mutation in a completely different protein e. Why are second site suppressor mutations allele specific? f. There is a special type of complementation called allelic complementation in which your answer to part c does not hold true; allelic complementation is caused by a specific type of pseudo-reversion in which the two mutant organisms each have a mutation in different parts of the same gene (for example, let's consider geneX: mutant 1 has a mutant allele of geneX, say X-1, while mutant 2 has a different mutant allele of geneX, X-2) Could allelic complementation be an indicator that a protein acts as a homomultimer, why or why not?Explanation / Answer
1. a) A dominant negative phenotype indicates a protein may be acting as homomultimer. When the wild type version of protein is present along with a mutant version, a mixed multimer can be formed. A dominant negative mutation disrupts the activity of wild type protein in the multimer.
The dominant negative mutation may arise in a human somatic cell and provides a proliferative advantage to the mutant cell, leading to its clonal expansion.
b) Hypermorphic mutation does not indicate a protein acting as a homomultimer because in such mutations the altered gene product possesses an increased level of activity or in which the wild type gene product is expressed at an increase level.
c) It means that the mutations are in different genes. It occurs when two strains of an organism with different homozygous recessive mutation that produce the same mutant phenotype, produce offspring with the wild type phenotype when mated.
d) A mutation in one protein can rescue the phenotype caused by mutation in a different protein. This occurs because mutation in interacting genes are often isolated as suppressors. Sometimes a mutant protein can be restored to wild type.
This type of mutation is a second mutation that suppresses the original mutation by restoring the reading frame, as long as the portion between two mutations is not critical for protein function.
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