Unit 6 FRQ (Genetic Mutations)

Unit 6 FRQ (Genetic Mutations)

AP Bio Free Response Question: Genetic Mutations

👋 Welcome to the AP Bio Unit 6 FRQ on Genetic Mutations. These questions are a bit longer, so grab some paper and a pencil, or open up a blank page on your computer to follow along.

⚠️ (Unfortunately, we don’t have an Answers Guide for this question, but this will give you a good idea of how an FRQ for Unit 6 might appear on the exam.)

⏱ Remember, the AP Biology exam has 6 free-response questions, and you’ll have 90 minutes for the entire FRQ section. That means you should aim to spend about ~15 minutes on each practice FRQ.

🤔 Need a refresher for the unit as a whole? Check out the Unit 6 Overview (Coming soon!). If you’re getting stuck halfway, don’t hesitate to explore the Unit 6 resources for additional help.

Setup

GRP143 is an X-linked gene that contains instructions for producing a protein that regulates melanosomes—organelles that produce and store melanin pigments. The expression of GPR143 is controlled by microphthalmia-associated transcription factors (MITF). MITF plays a role as a regulator of melanin synthesis in humans. Mutations in this gene can lead to ocular albinism, a recessive genetic disorder that reduces pigment production in both the front and back of the eye, affecting the iris and retina. Individuals with ocular albinism are born with vision impairments, which result in poor image sharpness and depth perception.

A pediatrician is seeing a mother and father who are concerned about their 10-month-old child. They report that their child has not tracked them with her eyes since she was six months old. The child presents as female and has very light-colored eyes. The mother has read about ocular albinism on WebMD and suspects her child might have the disorder.

Questions

(a) Explain why the pediatrician may agree or disagree with the parent’s hypothesis.

The pediatrician may agree with the parent’s hypothesis because the child shows several common signs of ocular albinism, such as lack of eye tracking and very light-colored eyes. These symptoms are consistent with reduced melanin production in the iris and retina, which can impair vision and light sensitivity.

However, the pediatrician may disagree with the parent’s hypothesis because ocular albinism is an X-linked recessive disorder, meaning it is less common in females compared to males, as females would need two copies of the mutated gene to be affected. If the child only has one copy of the mutated gene, she may be a carrier but not show symptoms of the disorder. Additionally, other conditions, such as congenital nystagmus or strabismus, could explain the child’s symptoms.

(b) In studies of GPR143 mutations, mice are often used because they have a similar genetic makeup. The mouse version of the gene comprises a polypeptide that is 404 amino acids long. GPR143 mutations most commonly involve the change of a single base pair in the gene sequence. Identify the type of mutation that occurs.

The type of mutation that occurs is most likely a point mutation. Point mutations involve the change of a single nucleotide base in the gene sequence, which may lead to changes in the resulting amino acid in the polypeptide chain. This type of mutation can result in a missense, nonsense, or silent mutation, depending on how the altered codon affects the amino acid sequence of the protein.

(c) MITF regulates the expression of GPR143 and other genes associated with melanin production. Predict a disorder that may result from a dysfunctional MITF gene.

A dysfunctional MITF gene may result in a disorder such as Waardenburg syndrome, which affects pigmentation in the skin, hair, and eyes and can also cause hearing loss. Since MITF plays a critical role in regulating genes involved in melanin synthesis, mutations in MITF can disrupt melanin production and lead to phenotypic changes in pigmentation and sensory issues.

(d) Tietz syndrome is caused by mutations in the MITF gene. It results in pigment changes in the skin, hair, and eyes, as well as hearing loss. The mutation is due to a deletion in the MITF gene. Explain how the mutation of the MITF gene results in such a profound phenotypic impact, emphasizing the regulation of gene expression mechanisms.

The deletion in the MITF gene causes a profound phenotypic impact because MITF is a transcription factor that regulates the expression of several genes involved in melanocyte development and melanin synthesis. A deletion mutation can lead to a loss of function of the MITF protein, meaning it can no longer effectively bind to DNA and activate transcription of target genes. This results in a reduction in melanin production, causing changes in pigmentation in the skin, hair, and eyes.

Additionally, MITF is involved in the differentiation and survival of melanocytes, as well as cells in the inner ear. The deletion of the MITF gene disrupts these processes, leading to hearing loss due to improper development of melanocytes that contribute to the function of the inner ear. Therefore, a dysfunctional MITF gene affects multiple aspects of development and results in widespread phenotypic effects.