USABO OPEN EXAM 2024
QUESTIONS WITH A
GRADE SOLUTIONS
Last year, Katya joined five of her best friends for an adventure rafting 42 miles on the
Tara River in Montenegro's Durmitor National Park. One evening, they pulled into the
bank to rest and have dinner. Katya decided she would explore the area for few wild
strawberries and found very few of them. She gathered all the strawberries she saw and
brought them back for the group to have on their pancakes the next morning. Katya had
such a wonderful time that when her friend Charles asked her to do the trip again, she
readily agreed. They made port in the same spot as last year and again, Katya with
Charles sought out strawberries. This time though, the hillsides were covered with wild
strawberries and they gathered only the largest and most ripe berries for their
pancakes. This is an example of:
A. Associative learning
B. Cognitive thinking
C. Operant conditioning
D. Optimal foraging
E. Trial-and-error learning - Answer-D. Optimal foraging
Which of the following is NOT a reason that Drosophila melanogaster was originally
used as a model organism in Thomas Morgan's 1907 genetics experiments?
A. Generation time is brief.
B. It has only four chromosomes, which are easily visible.
C. It reproduces prolifically.
D. It was easy to manipulate genetically.
E. It is a relatively simple organism to breed in the lab. - Answer-D. It was easy to
manipulate genetically.
Which of the following is correct?
A. Acetylation of histones facilitates expression of the DNA associated with the
acetylated histone.
B. Methylation of DNA facilitates expression.
C. G proteins attaching to histones facilitate expression of DNA.
D. Deacetylation of histones facilitates expression of DNA wrapped around the
acetylated histone.
E. Methylation of histones facilitates expression of DNA wrapped around the acetylated
histone. - Answer-A. Acetylation of histones facilitates expression of the DNA
associated with the acetylated histone.
, Which of the following could NOT be the blood type of a child born to a mother with AB+
blood and a father with B- blood?
A. A+ B. AB C. O+ D. A. E. AB+ - Answer-C. O+
X- linked agammaglobulinaemia is a rare X-linked disorder that interferes with the body's
ability to fight infection. A man with X-linked agammaglobulinaemia marries a woman
who is not affected. Which of the following best predicts their children's potential for
inheriting X-linked agammaglobulinaemia?
All their children, regardless of sex, will have X-linked agammaglobulinaemia.
A. All their sons will have X-linked agammaglobulinaemia, and all their daughters will be
carriers.
B. Approximately 50% of their daughters will have X-linked agammaglobulinaemia, and
all their sons will be normal.
C. Approximately 50% of their sons will have X-linked agammaglobulinaemia, and all
their daughters will be carriers.
D. None of their children will have X-linked agammaglobulinaemia, but their daughters
will be carriers. - Answer-E. None of their children will have X-linked
agammaglobulinaemia, but their daughters will be carriers.
In a population of papillons that contains genetic variation under the influence of natural
selection, what is the correct sequence of the following events?
I. Allele frequency within the population change.
II. Differential reproduction occurs.
III. Environmental changes occur.
IV. New selective pressures occur.
A. IV, III, II, I
B. IV, III, I, II
C. III, II, IV, I
D. III, IV, II, I
E. III, IV, I, II - Answer-D. III, IV, II, I
Which of the following pairs represent two distinct species?
A. House mouse, Fancy mouse
B. Mayan Indian, Inuit Indian
C. Monarch butterfly, Viceroy butterfly
D. Papillon, Chihauhau
E. Soldier ant, Drone ant - Answer-C. Monarch butterfly, Viceroy butterfly
Olney, IL, is known for its white squirrel population. In this squirrel population, assume
that 10% of the genes are for albino coat color and 90% are for gray coat. If
HardyWeinberg assumptions are true, what percentage of the squirrels are
heterozygous?
A. 90 B. 81 C. 18 D. 9 E. 1 - Answer-C. 18
