Unit 6 FRQ (Genetic Mutations)

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

⚠️ (Unfortunately, we don't have an Answers Guide for this question, but it can give you an idea of how an FRQ for Unit 6 might look on the exam.)

⏱ The AP Biology exam has 6 free-response questions, and you will be given 90 minutes to complete the FRQ section. (This means you should give yourself ~15 minutes to go through each practice FRQ.)

GRP143 is an X-linked gene contains directions for the construction of a protein that controls melanosomes, which are organelles that produce and house melanin pigments. Expression of GPR143 is controlled by microphthalmia-associated transcription factors, or MITF. MITF occurs in humans as a regulator for melanin synthesis. Mutations of this gene result in ocular albinism. Individuals with ocular albinism have a recessive genetic disorder that reduces the amount of pigment at the front and back of the eye. The iris and the retina are both affected, which impacts the eye’s ability to detect light. As a result, individuals with ocular albinism are born with vision impairments that result in low image sharpness and low depth perception.

A pediatrician sees a mother and father with a ten-month-old child they are concerned about. They state the child has not tracked them (followed them with its eyes) since they became six-months old. The child presents as female and has very light eyes, and the mother has read about a disease called ocular albinism on WebMD. She thinks the child has ocular albinism.

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

(b) In studies of GPR143 mutations, mice are often used because they have a very 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 from the gene sequence. Identify the type of mutation that occurs.

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

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