Table 3 

GCA questions for which students had an MCIA

QuestionSummary of most common incorrect ideaRepresentative quote from student interviews
Question 1: Which of the following human cells contains a gene that specifies eye color?Different cells in individuals contain different genes.“Gametes have everything that determine eye and skin cells. So the heart has nothing to do with eye color. So the genes will not be there.”
  a. Cells in the eye (1.6%)
  b. Cells in the heart (0.1%)
  c. Gametes (sperm and egg) (7.6%)
  d. Cells in the eye and gametes (20.2%)
  e. All of the above (70.4%)
Question 3: An inherited disease that affects women and not men is likely to be caused by:Inherited diseases that affect only women are caused by mutations on the X chromosome“Because women have two copies. I don't think it is on the autosomes because they have nothing to do with sex.”
  a. A mutation in a gene on the X chromosome, which is a sex chromosome (23.6%)
  b. A mutation in a gene on a non-sex chromosome (autosome) (14.2%)
  c. without additional information, either answer a or b is possible (61.7%)
A small percentage chose d or e.
Question 4: Suppose that a single DNA base change of an A to a T occurs and is copied during replication. Is this change necessarily a mutation?A change is a mutation only if it will produce a change in the amino acid sequence.“There are many sequences that code for the same amino acid, so you can have a DNA change but not get a change in the amino acid; to get a mutation, you have to change the amino acid.”
  a. Yes, it is a change in the DNA sequence (70.0%).
  b. Yes, if the base change occurs in a gamete (sperm or egg cell); otherwise, no (0.8%).
  c. Yes, if the base change occurs in the coding part of a gene; otherwise, no (3.7%).
  d. Yes, if the base change occurs in the coding part of a gene and alters the amino acid sequence of a protein; otherwise, no (24.9%).
  e. Yes, if the base change alters the appearance of the organism (phenotype); otherwise, no (0.5%).
Question 10: Cystic fibrosis in humans is caused by mutations in a single gene and is inherited as an autosomal (non-sex chromosome) recessive trait. A normal couple has two children. The first child has cystic fibrosis, and the second child is unaffected. What is the probability that the second child is a carrier (heterozygous) for the mutation that causes the disease?When two heterozygotes mate, probability calculations do not need to be adjusted even if an offspring is known to be unaffected.“1/2 since both parents are carriers for a child to have a recessive trait. Each pair has a 1/2 chance of passing on the trait.”
  a. 1/4 (4.1%)
  b. 1/2 (43.0%)
  c. 2/3 (50.5%)
  d. 3/4 (1.3%)
  e. 1 (1.1%)
Question 11a: The following DNA sequence (coding strand) occurs near the middle of the coding region of a gene: 5′-A A T G A A T G G G A G C C T G A A G G A G-3′. Which of the following DNA mutations is almost certain to result in a shorter-than-normal mRNA?A stop codon stops transcription.“Both transcription and translation will stop early if there is a stop codon.”
  a. A→G at position 50 (2.0%)
  b. G→A at position 53 (46.5%)
  c. C→A at position 58 (1.6%)
  d. None of the above (49.5%)
A small percentage chose e.
Question 12: For the same DNA sequence, which of the following DNA mutations is almost certain to result in a shorter-than-normal protein?A frameshift mutation cannot lead to an early stop of translation.“You insert something and get extra… how would you get a shorter protein? Inserting something would give you a longer protein. The only way to get a shorter protein is to take away a nucleotide.”
  a. T→C at position 59 (0.7%)
  b. A→G at position 61 (2.0%)
  c. Insertion of a G after the G at position 54 (62.6%)
  d. None of the above (34.5%)
A small percentage chose e.
Question 15: You have identified a previously unknown human gene that appears to have a role in autism. It is similar enough in DNA sequence to a known mouse gene that you believe that the two genes may be evolutionarily related. You determine and compare the DNA sequences, the predicted mRNA sequences, and the predicted amino acid sequences corresponding to the two genes. You would expect to find the greatest sequence similarity from comparisons of the two:DNA and amino acid sequences are equally variable.“If the DNA is similar, the mRNA is similar, and the amino acid will be similar to the DNA, so they must be the same.”
  a. DNA sequences (13.6%)
  b. mRNA sequences (3.9%)
  c. Amino acid sequences (51.5%)
  d. All three comparisons are likely to show the same degree of sequence similarity (31.0%)
Question 20a: Sue's chromosome 18 pair looks like this: (AA). Bob's chromosome 18 pair looks like this: (Aa). Bob and Sue have a stillborn son with three copies of chromosome 18 that look like this: (AAA). In which parent did the chromosome separation problem occur?Chromosome separation errors happen only in meiosis I.“Child has trisomy so one pair failed to separate; it must be from Sue because she has two As.”
  a. Sue (54.2%)
  b. Bob (1.2%)
  c. You need additional information to determine which parent (44.5%).
A small percentage chose d or e.
Question 21: You are interested in studying a gene called CFTR because mutations in this gene in humans cause cystic fibrosis. You have made a line of mice that lack the mouse CFTR gene. These mice are unable to clear bacteria from their lungs, so they get lung disease. You put a normal human CFTR gene into some of these mice and discover that the mice with the human gene are able to clear bacteria from their lungs and no longer get lung disease. From this experiment, you can conclude that:If proteins have the same function, they must have identical amino acid sequences.“Proteins have to have the same function and the same sequence.”
  a. The DNA sequences of the mouse CFTR gene and human CFTR gene are identical (0.7%).
  b. The amino acid sequences of the mouse CFTR protein and the human CFTR protein are identical (1.1%).
  c. The mouse CFTR gene and human CFTR gene encode proteins that can serve a similar function (70.9%).
  d. Both answers b and c are true (20.8%).
  e. All of the above are true (6.5%).
  • Questions, the frequency of each posttest answer, a summary of the most common incorrect idea, and a sample quote from student interviews are shown for the nine questions explored further in this study.

  • a Question is abbreviated here; see Figure S1 for the full question.