Fall 2003: Lecture Exam 2

This exam consists of 50 multiple-choice questions. Each one has only one right answer. Read each question and all possible answers carefully before answering. Please mark your answers on the Scantron form provided, using only #2 lead pencil. If you erase an answer, make sure you erase it fully, or the machine may mark it incorrect. Check carefully to ensure that your answers are on the correct rows on the Scantron form.

Turn in both the Scantron form and the test paper when you are finished. Make sure your name is on both. You may write on the test paper if you wish, but anything you write on the test paper will not be graded. Good luck.

A certain wildflower called "blue-eyed Mary" (Collinsia parviflora) is normally blue, as the name suggests. However, magenta flowers and white flowers are also known in this species. These flowers have their colors because they contain pigments called anthocyanins. Different anthocyanins in the flower cells give the flower different colors.

1. To make anthocyanin pigments, cells use enzymes. Enzymes are members of a class of large molecules called
proteins

2. Each enzyme molecule is a complexly folded strand of subunits called
amino acids

3. Enzymes cause chemical reactions to happen by lowering their
activation energy

4. Any substance, whether it's an enzyme or not, that causes chemical reactions to happen in the way described in question 3 may be called
a catalyst.

5. Where are enzymes made?
On ribosomes.

6. The process by which an enzyme molecule is actually assembled is
translation.

7. If you denature an enzyme, you can stop it from doing what it normally does by
altering its shape.

8. A particular enzyme-just call it M-normally takes a white pigment in the flower and turns it into a magenta pigment. The basic "instructions" that the flower's cells use to assemble enzyme M are
a gene.

9. Those "instructions" come in several forms. The M form makes an enzyme that converts white to magenta, while the m form makes an enzyme that is inactive-an enzyme that doesn't convert white pigment to magenta pigment. These "alternate forms" are known as
alleles.

10. If I simply listed the order of the subunits that enzyme M is made of, I would be describing its
primary structure

11. A second enzyme, which we'll call enzyme B, also comes in two "versions": B converts magenta to blue, and b doesn't. Neither version of enzyme B does anything to white pigment. If I describe a particular plant as "MmBb", I've described the plant's
genotype.

12. Suppose I cross two blue-eyed Mary plants, both of which are MmBb. I might expect to get a certain ratio of different types of flower. What would I expect the ratio to be?
9 blue: 3 magenta: 4 white.
This was the evil part. . . Why'd we get four white? Because enzyme B can only turn magenta pigment blue. . . it can't turn white pigment blue, which was stated in #11. So the plants with genotypes mmBB and mmBb (as well as mmbb) will produce white flowers.

13. A cell with 28 chromosomes undergoes mitosis. How many chromosomes do the daughter cells have?
28

14. In fruit flies, a single gene called claret has been identified that causes the eyes to become dark red (they're normally bright red). Flies with claret eyes also produce abnormal eggs or sperm cells. This is an example of
pleiotropy.

15. The process of cytokinesis is defined as
an entire cell pinching or splitting into two.

16. This is the formula for the amino acid isoleucine. What is the part of the molecule called that's labeled 1? The R group. 17. Which part of the isoleucine molecule would form a peptide bond with the carboxyl group of a neighboring amino acid? #2. Because #2 is the amino group.

18. During the process of translation, isoleucine is brought to the ribosome and "put into position" by a "clover-leaf"; molecule known as
transfer RNA.

19. Babies born with the very rare condition called Edwards's syndrome rarely live past one year of age. They typically are born with severe heart and kidney defects, joint and muscle malformations, malformed ears and feet, small heads, mental disabilities, and sometimes other problems. Edwards's syndrome is also known as trisomy-18, meaning that affected infants have, in each cell,
three copies of chromosome 18.

20. Edwards's syndrome is probably caused by a mistake in
meiosis forming either the mother's egg or the father's sperm.

21. Most cells in a normal human are diploid, meaning that they
contain two copies of each chromosome.

The disorder familial adenomatous polyposis, or FAP, causes a large number of growths, called "polyps", to grow out of the wall of the large intestine (the colon and rectum). These growths can easily turn cancerous; untreated persons with FAP have a very high risk of colon or rectal cancer. FAP is controlled by a single gene with two alleles: normal (F⁺) and polyp-causing (F^-).

22. A Website about FAP that I was reading states that "Each child, boy or girl, born to a person with FAP has a 50:50 chance of inheriting the gene that causes it." This isn't quite the whole story; what the Website meant was that each child born to one parent with FAP and one parent without FAP has a 50:50 chance of inheriting the gene. This implies that
F^- is dominant and F⁺ is recessive.
This one was tough, but you can solve it by eliminating alternatives. We know it's not sex-linked or on the X chromosome, because the risk is equal for boys and girls. If the alleles were codominant, then you could both have and not have FAP at the same time, which doesn't work. If FAP were recessive, then a person with FAP would have to be be F^-F^- -- and all of his children would inherit the FAP-causing gene. The only way for the Website to be accurate is if FAP is caused by a dominant allele. That way, a FAP sufferer is heterozygous (F^-F⁺)-- and his kids each have a 50-50 chance of getting the F^- allele.

23. Suppose that two people with FAP happened to marry and have children. What would the odds be that their first child would have FAP as well?
75%.

24. At the start of cell division, chromosomes become visible under the microscope; careful examination shows that they resemble tiny X's. Each half of an X-shaped chromosome is a/an
chromatid.

25. The Punnett square was invented by
Reginald H. Punnett.
Duh!

The 1993 movie Lorenzo's Oil was based on the real case of a boy with a rare disease called adrenoleukodystrophy, or ALD. This can be lethal in childhood, but adults sometimes develop a less severe form of ALD later in life. ALD is a sex-linked trait on the X chromosome.

26. A woman with no family history of ALD marries a man with ALD. They have ten sons. About how many of them would be expected to develop ALD?
none of them
Why? Let a normal X chromosome be written X⁺, and an X chromosome with the ALD gene be written X^A. A woman with no family history of ALD is presumably X⁺X⁺; a man with ALD is X^AY. The man gives a Y chromosome to all his sons -- that's what makes them his sons and not his daughters, by definition! None of his sons can inherit his X^A chromosome, all of his sons should get normal X⁺ from Mom, and none would be expected to develop ALD.

27. The same couple also has ten daughters. About how many of them would be expected to develop ALD?
none of them
Same reasoning as above: all daughers will inherit an X⁺ from Mom and X^A from Dad, making them carriers. But wait! How do we know that ALD is recessive? If it's not, then all the daughers will develop ALD! The clue's in the next question: if normal parents have an ALD son, the ALD gene must have been passed on by a normal mother, and ALD must be recessive.

28. Suppose a normal man and a normal woman have a son who develops ALD. Their next child is a daughter. What are her chances of developing ALD?
0% (she will never have ALD)

29. People with ALD cannot break down certain lipids called "very long-chain fatty acids" or VLCFAs. This causes these to build up in the brain, leading to damage. This probably means that ALD patients cannot make a particular _____ that would normally break down the VLCFAs.
enzyme

30. Which of these is a valid difference between meiosis and mitosis?
Meiosis starts with chromosomes pairing up and crossing over; this doesn't happen in mitosis.

31. Genes close to each other on a chromosome may be inherited as if they were a single gene. This is
genetic linkage.

32. Heat can break apart the hydrogen bonds that hold a DNA molecule together. This causes the molecule to
"unzip" into two strands

33. In the "genetic code", the group of three bases ACC "stand for" the amino acid serine. ACC is
a codon.

34. An alpha-helix is an example of a protein's
secondary structure.

35. Fifty years ago last Wednesday, Francis Crick and James Watson published the first results of their research on DNA. Their results may be summed up as
DNA has the shape of a double helix.

36. In which of the following situations would you expect to find a lot of mitosis going on?
All of the above. (Development of an embryo; lung cancer; and healing of a wound.)

37. A British insect known as the "tiger moth" may have several wing color patterns. Some moths have six white spots on the wings; others have only two spots. The gene that controls this trait shows incomplete dominance between two alleles. This means that if you cross a purebred six-spotted moth and a purebred two-spotted moth, you should get
all four-spotted moths.

38. Special cells in your immune system, called plasma cells, produce large amounts of proteins (called antibodies) that defend you against infections. Based on what they do, we might predict that these cells should have a lot of
ribosomes.

On a cold snowy Christmas Eve in 1962, a baby was left on the steps of the Millville Orphanage and Home for Wayward Foundling Children. That baby grew up to become the wealthiest financier on Wall Street, the billionaire J. Smedley Richman. Forty years later, Mr. Richman is searching for his birth parents, to share his fortune with them. He places an ad in the paper, and within days, hundreds of people show up claiming to be his parents.

39. Mr. Richman has type AB blood. This immediately enables him to reject
everyone with type O blood.

40. One couple claims that they're the true parents of Mr. Richman. He can expose them as frauds if
they both have type A blood.

41. Another couple claims to be Mr. Richman's parents. The mother has type A blood and the father has type B blood. They introduce Mr. Richman to their other child, his supposed sister, who has type O blood. If this couple really is Mr. Richman's parents, this means that the mother must have the genotype
AO

42. What are the odds that the couple mentioned in #41 would have had a child with type O blood? (Hint: you'll have to figure out the father's genotype first.)
One in four.
Remember that the only genotype that gives you O blood is OO -- i.e., you have to get an O allele from both Mom and Dad. If Sis is OO, then if Mom has type A blood she must have the AO genotype -- and Dad, who is type B, must have the BO genotype. If you do the Punnett square for a cross between an AO person and a BO person, you'll find an equal probability -- 25%, or one in four -- for each blood type.

43. What are the odds that the couple mentioned in #41 would have had a child with type B blood? (Hint: you'll have to figure out the father's genotype first.)
One in four.

44. What should Mr. Richman do with the people in #41?
Do further testing, because he can't be sure.

45. A portion of DNA begins as follows: TGACCATAAAAATTA. The complementary mRNA strand would have to read
ACUGGUAUUUUUAAU

46. Suppose you discover that a certain plant has DNA that is 27% adenine (A). You could use Chargaff's Rule to determine that
the DNA must contain 46% guanine + cytosine
Oooh, this was evil. . . Since A only pairs with T and T only with A, the amount of A equals the amount of T. So the plant's DNA is 27% A and 27% T, or 54% A+T. All the percentages of A, T, G and C add up to 100%, so the percentage of G+C = 100% - 54%, or 46%.

47. What do spindle fibers do?
Move chromosomes around during cell division.

48. Spindle fibers are most visible when a cell is in
metaphase or anaphase.

49. Gregor Mendel
discovered the rules governing how genes are inherited and expressed.

50. The capital of Arkansas is
Little Rock.
No, this was not a trick question -- which makes me wonder how it is that at least one person got it wrong. . .