Problem 6 - AP Psychology Premium Prep 2021

Question

Which of the following mutations would be least likely to have any discernable phenotype on the individual? (A) Translocation of the last 1,000 base pairs of chromosome 1 onto chromosome 2 (B) Nondisjunction of chromosome 7 to produce trisomy7 (C) Nondisjunction of chromosome 8 to produce monosomy-8 (D) Deletion of 400 base pairs, resulting in the loss of an enhancer

Step-by-Step Solution

Answer

The mutation least likely to have any discernable phenotype on the individual is (D) Deletion of 400 base pairs, resulting in the loss of an enhancer, as it only impacts a small subset of genes compared to the other mutation types.

Step 1: Understand each type of mutation

In order to determine which mutation is least likely to impact an individual's phenotype, we should first understand each type of mutation. (A) Translocation: Translocation is the process in which a piece of one chromosome breaks off and reattaches to another chromosome. In this case, the last 1,000 base pairs of chromosome 1 are translocated onto chromosome 2. (B) Nondisjunction: Nondisjunction is when chromosomes fail to separate properly during cell division. In this case, nondisjunction of chromosome 7 results in trisomy of chromosome 7, meaning the individual has three copies of chromosome 7 instead of the normal two copies. (C) Nondisjunction: Similarly, nondisjunction of chromosome 8 results in monosomy-8, meaning the individual has only one copy of chromosome 8 instead of the normal two copies. (D) Deletion: Deletion is the process in which a piece of DNA is lost during DNA replication. In this case, a 400 base pairs deletion results in the loss of an enhancer, which is a short region of DNA that can help regulate gene expression.

Step 2: Consider potential effects of each mutation on phenotype

Now, we will analyze the potential effects each mutation may have on an individual's phenotype. (A) Translocation might lead to changes in gene expression and formation of fusion genes, which could potentially affect the phenotype. (B) Trisomy 7, having an extra copy of chromosome 7, can lead to multiple issues due to gene dosage imbalance. This could have significant effects on an individual's phenotype. (C) Monosomy-8, having only one copy of chromosome 8, can lead to a lack of essential genes and cause many problems. This could have a serious impact on an individual's phenotype. (D) Deletion of an enhancer may affect the gene expression regulation, although a single enhancer is typically only involved in regulating a small subset of genes and may not affect the individual's overall phenotype significantly.

Step 3: Compare the potential effects of each mutation

Comparing the potential effects of each mutation on phenotype: (A) Translocation may have some impact on phenotype, but it's not always detrimental. (B) Trisomy 7 is likely to have a significant impact on phenotype as there is an extra copy of an entire chromosome. (C) Monosomy-8 is also likely to have a significant impact on phenotype due to the lack of essential genes on chromosome 8. (D) Deletion of an enhancer may affect gene expression, but it's likely to have the least impact on phenotype compared to other mutations, as it only impacts a small subset of genes.

Step 4: Conclusion

Considering the potential effects of each mutation type, the mutation that is least likely to have any discernable phenotype on the individual is (D) Deletion of 400 base pairs, resulting in the loss of an enhancer.