Download Unit 3 Problem Set KEY unit3_problemset_key

Biology 100
Problem Set for Unit 3
1. If a particular gene has a sequence that is 21% A (among A, C, G, and T), what percent
can be deduced to be made up of G? 21% A means 21% T. That leaves 58% for C and G,
therefore 29% is G.
2. DNA has many properties that allowed us to isolate it in lab. For each property listed,
describe how we exploited that property in the DNA isolation.
a) VERY long twisting it around the hooked pipette
b) Negatively charged solubility change between water and salty water with ethanol
c) Soluble in water ethanol precipitation
3. Use the following terms to correctly describe how information in DNA determines our
response to drugs using CYP3A4 as an example:
DNA sequence
Protein sequence
Protein function
Neuron function
A different DNA sequence for this gene is a new allele. New alleles have the potential to
encode different proteins both in their sequence and therefore potentially in their
functionality. Different protein function (in this case more or less enzyme activity) means
more or less drug available to impact the neuron.
4. Two people mate who are both HETEROZYGOUS for blood type A – a trait that shows
Mendelian (not incomplete) dominance.
a) What are their phenotypes? Blood type A What are their genotypes? AO is the
conventional way to describe this. But Aa would work just fine.
b) What phenotypes will be seen in what PROPORTIONS for their kids (assuming an
infinite number of kids)? 3/4 will have blood type A, 1/4 will have blood type O
c) What type(s) of kid would they NOT be likely to have? Could not have type B or type
AB.
5. Tasting a bitter chemical is probably NOT a dominant trait but an incompletely dominant trait.
Super tasters have two contributing alleles, tasters only one and non tasters – no contributing
alleles. Whistling is a recessive trait controlled by a gene that shows Mendelian dominance.
a) What is the genotype of a Taster who can whistle? Tt ww
b) What is the genotype of a Taster who cannot whistle, but whose mother could? TtWw
c) If the people described in a) and b) mate, what proportion of their children will be
whistlers? 1/2 of their kids will be ww (1/2 will be Ww).
d) If the same people mate, what proportion of their children will whistle and be non-tasters?
1/4 of their kids will be non-tasters (tt). 1/4 x 1/2 or 1/8 will be whistler, non-tasters.
6. Two people who are heterozygous (Rr x Rr) mate. Among their kids there are THREE
different phenotypes. How is the trait controlled by gene R inherited?
Must show incomplete dominance, a different phenotype for all three genotypes (RR, Rr, and rr).
Biology 100
Problem Set for Unit 3
7. Congenital amusia is a condition wherein affected individuals have absolutely NO musical
abilities, can’t tap out rhythms, can’t carry a tune, etc. This trait is inherited as a recessive trait.
Make a pedigree that would show how this trait is inherited and shows clearly that it is NOT
dominant.
Two people without the trait have a child with the trait.
8. If identical twins are concordant for Congenital amusia, does this alone show that the trait is
genetically controlled? Careful!
Not necessarily – could be a non-genetic trait that is controlled by their shared environment.
9. If QqRrSs x qqRrSS, and all three genes contribute additively to a trait solve the following
questions:
a) Make three Punnett squares for this mating One for gene Q, one for gene R, one for S
b) Complete a branch diagram for the mating
SS
RR
Ss
SS
Qq
Rr
Ss
SS
rr
Ss
SS
c) Determine the probability of all genotypes
for children from this mating All genotypes
with RR or rr have a 1/16th probability. All
genotypes with Rr have a 1/8th probability.
d) Make a distribution graph for the possible
phenotypes of the children from this
mating.
RR
Ss
SS
qq
Rr
Ss
SS
rr
Ss
3
3/8
1/8
2
1/16
1
4
5
10. Examine the accompanying pedigree where a solid black symbol shows someone with severe
drug allergy, a striped symbol shows someone with a mild allergy, and an open symbol shows
someone with no drug allergy.
Biology 100
Problem Set for Unit 3
a) Assuming this trait is controlled by ONE gene, what can we assume about the way this
gene controls the phenotype of drug allergy? Incomplete dominance (based on three
phenotypes, not pedigree)
b) What is the genotype of the person designated by the arrow? Aa
c) If this woman were to have a child with a strong drug allergy, what can we assume about
her mate? Her mate must either have a strong allergy or a mild one.
d) Is it possible for this pedigree to represent a trait controlled by two genes? Absolutely.