1) (1 pt) Retinitis pigmentosa is actually a group of diseases. In other words, similar
symptoms can be caused by mutation in one of several different genes. What is the
term that we use to describe a disease that could be caused by mutations in different
c) (4 pts) The break point of this translocation on chromosome 3 cuts right through the
middle of a gene called Rho. Mutations of Rho cause autosomal dominant forms of RP.
With this information in mind, propose a mechanism of how the translocation causes
retinitis pigmentosa. Draw a diagram of the translocation in chromosomes 3q and 5q.
4) A mutation in a gene called PRPF6 causes another form of retinitis pigmentosa. Part
of the wildtype amino acid sequence of this protein is aligned for different species. The
arrowhead on the top is pointing to the amino acid (R) that is mutated in the disease.
(Shaded letters are pointing out some differences between sequences).
d) (2 pts) Look at the second place in the sequence. Most of the non-animals have an
amino acid in this location, but the animals have a space. What could have caused this
difference in the sequences?
d) (5 pts) The PRPF6 mutation makes the spliceosome less functional. You would think
this would have widespread effects on the body, but the only symptoms are blindness.
Explain how a mutation in PRPF6 could only affect the retina. There are a couple of
reasonable explanations, so just explain one.
9) (4 pts) Usher syndrome causes both retinitis pigmentosa and hearing impairment.
One recessive form of Usher syndrome is caused by loss of function of the cell-adhesion
protein called Cadherin 23. Cadherins are expressed on the surface of cells and help
hold cells together in tissue. Cadherins are sometimes mutated in cancer cells. Think
about the progression of cancer and explain how mutation of cadherins could help
cancer cells. Would these mutations in cadherin be acting like tumor suppressors or
oncogenes? Hint: think about the nature of the mutations.
11) A form of RP that is common in people of Jewish ancestry is caused by an Alu insert
in exon 9 of a gene called MAK.
a) (2 pts) What is Alu? Circle all the answers that are correct
i. Short interspersed element (SINE)
ii. Microsatellite repeat
iii. Simple transposon
v. Inverted repeat
vi. Common repetitive sequence found in human genome
vii. A promoter that drives expression of the MAK gene
viii. A jerk for messing up our genes [don’t circle this one]
b) (3 pts) You suspect your patient has this form of RP. How could you do a genetic test
for this specific genetic abnormality (sequencing doesn’t count)? Explain the procedure
and the expected results if the patient has the Alu insert.
12) In this problem, we are dealing with an X-linked recessive form of RP.
a) (4 pts) A heterozygous female mates with an unaffected male. What’s the probability
that their son will have the disease (the son is already born)?
b) (4 pts) The heterozygous mom is actually losing her vision in one eye and the other
eye is normal. How is this possible given that this is a recessive disorder?
15) Scientists are busy working on treating retinitis pigmentosa with gene therapy. It is
fairly easy to get DNA into the retina, so this very well might be the first place
CRISPR/Cas9 will be used in humans. A recent paper described an experiment to edit
the genome of a rat model of a dominant form of RP. This form of RP is caused by a
mutation in Rho, which changes the codon for serine 334 into a stop codon, creating a
slightly shorter protein. (FYI: These experiments did improve eyesight in the rats).
a) (4 pts) It has been shown before that having only one copy of wildtype Rho leads to a
wildtype phenotype. Therefore, we can remove the mutant form of Rho and that
should “cure” these rats. What does this information tell us about the nature of this
dominant mutation? Think about the three main ways that mutations can act
b) (4 pts) They made a transgene (part (a) in figure below) that they packaged into a
virus and injected into rat eyes. Part (b) of the figure shows the targeting strategy. They
designed their guide RNA, so it would only cut the mutant (S334) allele and not the
wildtype allele. Remember, they are trying to just get rid of the mutant allele, not fix it.
Look at the diagram above (part b) and explain how they targeted only the mutant
17) (8 pts) Let’s finish with a concept map! Use the terms in one of the word banks to
create an accurate and cohesive concept map. You choose which set of words you want
to use, but you must use all the words within that set. Every word must have at least
one connection with the whole concept map. Every linkage must use a word or phrase
to describe the connection. Only make one concept map total, using only one set of
words. Feel free to use another piece of paper.
Choose one set
Set #1: DNA, heterochromatin, histone acetylation, mRNA, microRNA, RNA polymerase,
TATA box, transcription,
Set #2: chromosome inversion, genetic variation, haploid, homologous chromosomes,
karyotype, meiosis II, mutation, prophase I, recombination
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1) Retinitis pigmentosa is actually a group of diseases. In other words, similar symptoms can be caused by mutation in one of several different genes. What is the term that we use to describe a disease that could be caused by mutations in different genes?
The term that we use for this kind of disease is genetically heterogeneous.
c) The break point of this translocation on chromosome 3 cuts right through the middle of a gene called Rho. Mutations of Rho cause autosomal dominant forms of RP. With this information in mind, propose a mechanism of how the translocation causes retinitis pigmentosa. Draw a diagram of the translocation in chromosomes 3q and 5q.
Since the break-off point is within the Rho gene, one part of the Rho gene will be translocated to the q arm of chromosome 5. Such interruption will impair the integrity of the gene and the information written at this locus is partially transferred to the other chromosome. Such a gene is now truncated and can only encode part of the previous protein. As a result of this mutation, the gene loses genetic information encoding protein domains, without...