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Item CA033003: The DNA sequence of similar genes in different organisms can differ at certain locations because of mutations that occur in those genes.

Dogs, pigs, and cats have similar genes for traits that they have in common, such as four legs, tails, and a rib cage. One of those genes, Gene X, is pictured above. Why does the DNA sequence of Gene X differ in some positions (highlighted in red) for dogs, pigs, and cats?

  1. Over time, the organisms’ traits changed, which caused Gene X to change.
  2. Over time, mutations occurred in Gene X.
  3. All three organisms had different needs, so they intentionally created different genes.
  4. Not enough information is given.

Pre-Test

Distribution of responses (prior to studying evolution in high school)
Answer Choice
Overall
Grades
Gender
Primary Language
 
n = 580
6–8
n = 25
9–12
n = 514
Male
n = 254
Female
n = 286
English
n = 526
Other
n = 13
A. Over time, the organisms’ traits changed, which caused Gene X to change. 30% 32% 30% 29% 31% 30% 46%
B. Over time, mutations occurred in Gene X. 31% 32% 31% 34% 30% 31% 15%
C. All three organisms had different needs, so they intentionally created different genes. 31% 32% 30% 31% 30% 31% 23%
D. Not enough information is given. 8% 4% 8% 7% 9% 8% 15%

Post-Test (Control)

Distribution of responses (following typical high school instruction on evolution)
Answer Choice
Overall
Grades
Gender
Primary Language
 
n = 255
6–8
n = 15
9–12
n = 195
Male
n = 97
Female
n = 119
English
n = 205
Other
n = 6
A. Over time, the organisms’ traits changed, which caused Gene X to change. 25% 13% 25% 30% 22% 25% 50%
B. Over time, mutations occurred in Gene X. 42% 67% 39% 47% 36% 42% 17%
C. All three organisms had different needs, so they intentionally created different genes. 25% 7% 27% 15% 31% 23% 33%
D. Not enough information is given. 8% 13% 9% 7% 11% 9% 0%

Post-Test (Treatment)

Distribution of responses (following completion of an evolution curriculum module)
Answer Choice
Overall
Grades
Gender
Primary Language
 
n = 301
6–8
n = 8
9–12
n = 274
Male
n = 134
Female
n = 150
English
n = 274
Other
n = 9
A. Over time, the organisms’ traits changed, which caused Gene X to change. 25% 0% 26% 21% 25% 25% 22%
B. Over time, mutations occurred in Gene X. 52% 75% 51% 51% 53% 52% 33%
C. All three organisms had different needs, so they intentionally created different genes. 21% 25% 21% 25% 19% 20% 44%
D. Not enough information is given. 3% 0% 3% 3% 3% 3% 0%