Sadler, T. D. (2003). Informal Reasoning Regarding Socioscientific Issues: The Influence of
Morality and Content Knowledge. Unpublished Doctoral Dissertation, University of
South Florida.
Excerpts from pp. 84-88:
Data Collection
Test of Basic Genetics Concepts
For the assessment of understanding the science content that underlies genetic
engineering issues, this study required a test of genetics concepts. A review of the literature
related to genetics instruction and testing revealed no preexisting instruments that met the
specifications of the present study. Therefore, the investigator developed the Test of Basic
Genetics Concepts (TBGC). Instrument development began with the identification of target
concepts (see Appendix C for descriptions of each target concept). The concepts assessed in the
TBGC were derived by the investigator, who has spent time working as a geneticist in research
laboratories and teaching genetics as a component of high school biology and biotechnology
courses, in consultation with several general biology and genetics textbooks (Campbell, Mitchell,
& Reece, 1997; Gardner, Simmons, & Snustad, 1991; Klug & Cummings, 1997; Miller &
Levine, 1998). Multiple-choice questions designed to target each of the predetermined concepts
were written (see Appendix D for the questions). Because the TBGC is meant to assess basic
understanding, the instrument was developed for a high school level. The test was designed to
differentiate between individuals who have little to no understanding regarding the mechanisms
of human heredity and individuals who have a level of understanding commensurate with the
aims of high school genetics instruction. The TBGC did not distinguish among more advanced
levels of understanding that might result from successful completion of college genetics courses.
Forty-seven undergraduate students enrolled in general chemistry laboratory sections
took the TBGC (draft 2). One of the primary functions of this pilot test was determination of the
instruments’ ability to discriminate among individuals. The purpose of creating the TBGC was
to provide a means of selecting two sub-samples, one group that understood genetics and another
which had limited knowledge with respect to genetics. Therefore, the TBGC would not be
effective if it produced a limited range of scores, and the pilot test sought to assess the degree to
which the instrument could be used for its intent. The test produced a wide range of raw scores
varying from 5 (22%) to 23 (100%) items answered correctly. The distribution of scores
approximated a normal distribution (skewness=-0.16 ; kurtosis=-0.45 ) with a mean of 14.3 and
standard deviation of 4.3. Given these results, the investigator concluded that the instrument
could be used to differentiate between high and low understanding groups for the purposes of
this study. Results from the pilot test were also used to assess the instrument’s internal
consistency using the Kuder-Richardson estimate (KR20). Given the conservative nature of
Kuder-Richardson estimates (Mehrens & Lehmann, 1991), the calculated internal consistency
(rxx=0.79) suggests that the TBGC is appropriately reliable.
In addition to exploring the discriminatory power and reliability of the TBGC, the pilot
test also enabled item analyses. P values, the proportion of individuals who answered a
particular question correctly, were calculated for all questions and are presented in Appendix E.
The p values ranged from 0.90 indicating a very easy question to 0.27 indicating a very difficult
question. The average p value was 0.62 which suggests that the test is appropriately challenging
for the population sampled (Osterlind, 1989). Point-biserial correlation coefficients were also
calculated for each item (see Appendix E). The coefficients varied from 0.06 to 0.75. Although
all of the correlations were positive indicating that there were no questions on which low scoring
individuals outperformed high scoring individuals, seven questions possessed correlation
coefficients below 0.25 suggesting that these items did not perform as well as anticipated. Each
of these items was individually considered for improvement or omission. Two questions
(numbers 11 and 12, draft 2, see Appendix D) were removed from the test because the
investigator and reviewers perceived that the wording of the question could have been
misinterpreted by some test-takers. The possible answer choices on another question (number 7,
draft 2) were modified to improve the question. Although the remaining five questions were
carefully examined, no changes were made because the investigator, with consultation from the
content experts, deemed the questions appropriate for the purposes of the TBGC.
The investigator also examined all questions which possessed answer choices that were
not selected by any of the test-takers. An ideal question should contain a clear, correct choice
and plausible distracters. An answer choice that is not chosen by any test-takers suggests that it is
not functioning optimally (Osterlind, 1989). Twelve questions contained an answer choice that
was not selected. The investigator modified 3 of these distracters in an attempt to improve the
overall question. It was determined that modifications to the other 9 questions in this category
could potentially alter the intent or integrity of question; therefore, the investigator did not make
these changes. After a final review of the entire instrument, the investigator altered question 14
(draft 2 and final draft) because of its similarity to question 1 (draft 2 and final draft). The
modified question maintained its original content, but was sufficiently different than question 1.
None of the target concepts inherently possessed more importance for the purposes of
this investigation than any other; therefore, the investigator sought to have each concept equally
weighted on the TBGC. Each target concept was addressed by at least two questions. Four
questions addressed the concept regarding chromosome number in somatic and germ cells.
Because all of these questions were related to the same prompt, the investigator decided to retain
all four questions but halve their point value in order to maintain the same relative weighting for
each concept. The concept regarding the function of genes was addressed by three questions. In
order for this concept to be equally represented on the TBGC, one of the three questions (number
23, draft 2) was eliminated. Of the three items (numbers 8, 13, and 23, draft 2), question 23 was
the easiest (p=0.78) and the least discriminating (r=0.31); therefore, it was eliminated.
Excerpts from pp. 174-184:
Appendix C: TBGC Target Concepts
Table A-1. Concepts Assessed in the TBGC
Concept
Relationship between
DNA, genes, &
chromosomes
Description
Long strands of DNA make up chromosomes. Genes are localized
regions of chromosomes that help control the expression of certain traits.
Individuals of a species possess the same chromosome number and gene
sequence; however, except in cases of identical twins or clones, each
individual possesses a unique DNA sequence.
Chromosome number
in somatic & germ
cells
Somatic cells contain double the number of chromosomes found in germ
cells (i.e., sperm and egg cells). Whereas somatic cells contain pairs of
chromosomes, germ cells only contain one chromosome of each pair.
Dominance,
Recessiveness, &
Incomplete
dominance
The alleles of a particular gene may be dominant, recessive, or
incompletely dominant. In order for an allele to be recognized as
dominant, it must be paired with a recessive allele. The dominant allele
is expressed; whereas, the recessive allele is not expressed. In cases of
incomplete dominance, both alleles are expressed.
The function of genes
Genes control the production of cellular proteins. Specific genes are
activated in different regions of the body. The expression of many genes
is influenced by environmental conditions.
Physical location of
DNA
DNA is located inside the nuclei of cells. Every nucleated cell contains
a full set of chromosomes (with the exception of germ cells which
possess half of the chromosomes).
All living things
possess genetic
material
Inheritance
probabilities
All living organisms contain some form of genetic material. DNA is not
found in non-living objects.
Polygenic inheritance
Many human traits are controlled by multiple genes; therefore, the
inheritance of these traits does not follow Mendelian ratios and cannot
be determined by single-gene inheritance probabilities.
Genetic diseases
Several human conditions can be caused or influenced by an individual’s
genetic make-up. These genetic conditions may be the result of a single
gene, multiple genes, or chromosomal abnormalities. Gene therapy has
been proposed as a treatment for disorders caused by a single gene.
Inheritance probabilities for traits controlled by a single gene with
predetermined dominance patterns can be calculated.
Appendix D: TBGC Draft 2
Test of Genetics Concepts
Please circle the letter on the answer sheet which corresponds to the response which best answers
each item.
1. Which of the following does NOT contain genetic material?
a. mushroom
b. oxygen
c. tomato
d. tree
e. virus
2. Of the human cells listed below, which contain DNA?
I. blood cells
II. brain cells
III. liver cells
IV. reproductive cells
a. I only
b. II only
c. II and IV only
d. I, II, and IV only
e. I, II, III, and IV
The nerve cells of a particular animal species contains 20 chromosomes. Use this
information to answer the questions 3-6.
3. How many chromosomes would an unfertilized egg cell from this species contain?
a. 0
b. 5
c. 10
d. 20
e. 40
4. How many chromosomes would a fertilized egg cell from this species contain?
a. 0
b. 5
c. 10
d. 20
e. 40
5. How many chromosomes would a skin cell from this species contain?
a. 0
b. 5
c. 10
d. 20
e. 40
Appendix D (Continued)
6. How many chromosomes does any one individual animal from this species inherit from its
father?
a. 0
b. 5
c. 10
d. 20
e. 40
7. Which of the following statements is accurate regarding genetic traits that are determined by
multiple genes?
a. Inheritance probabilities of these traits can be predicted by using Mendelian ratios.
b. The dominant genes of these traits are usually inherited from the offspring’s mother.
c. These traits are usually sex-linked.
d. These traits usually have many phenotypes.
8. Which statement most accurately describes the function of genes?
a. genes control the production of DNA
b. genes control the production of protein
c. genes control cellular movement
d. genes control brain activity
9. Where in a cell is DNA located? (Assume the cell is eukaryotic.)
a. cytoplasm
b. cell membrane
c. nucleus
d. ribosome
e. vacuole
10. Which of the following does NOT describe genetic diseases?
a. genetic diseases are caused by infectious agents
b. genetic diseases are passed from parents to offspring
c. genetic diseases can be caused by a single gene
d. genetic diseases can remain latent for many years
11. Which of the following statements most accurately represents the relationship between
chromosomes, DNA, and genes?
a. DNA makes up chromosomes
b. chromosomes make up genes
c. genes make up DNA
d. chromosomes make up DNA
Appendix D (Continued)
12. What determines sex in human offspring?
a. 1 chromosome pair (the sex chromosomes)
b. 1 gene (the sex gene)
c. multiple genes throughout the genome (the sex determination complex)
d. mitochondrial DNA
e. sex determination is not genetic
13. Your muscle cells, nerve cells, and blood cells look different because each kind of cell
a. contains different kinds of genes
b. is located in different parts of the body
c. activates different genes
d. contains different numbers of genes
e. has experienced different mutations
14. Which of the following groups do NOT possess DNA?
a. animals
b. bacteria
c. fungi
d. minerals
e. plants
The presence of a facial freckles in humans is controlled by the expression of one gene with
two alleles. The “freckle” allele is dominant to the “no freckle” allele. (Assume that
dominance in this scenario refers to complete dominance.) Use this information to answer
the questions 15 & 16.
15. Juan and Carolyn both have freckles, but their daughter Katie does not. What does this
information indicate?
a. One of the parents carries a “no freckle” allele
b. Each of the parents carries a “no freckle” allele
c. Neither of the parents carry a “no freckle” allele
d. Katie carries at least 1 “freckle” allele
e. There is not enough information provided to make a conclusion
16. If Juan and Carolyn have another child, what is the probability that the child will have
freckles?
a. 0%
b. 25%
c. 50%
d. 75%
e. 100%
Appendix D (Continued)
17. Gene therapy would more likely be successful for conditions caused by
a. a single chromosome
b. a single gene
c. environmental influences
d. multiple chromosomes
e. multiple genes
18. The gene for human blood type possesses 3 alleles (A, B, & O). A and B are codominant
with one another, and both A and B are dominant to O. If a woman has type AB blood and a
man has type A blood, which of the following blood types could their children have?
a. A only
b. A or B only
c. A or AB only
d. A or B or AB only
e. A or B or AB or O
19. Hemophilia is an x-linked recessive disorder in humans. If a couple, both of whom do not
have hemophilia, have a son with the disease, what is the probability that their daughter would
also have hemophilia?
a. 100%
b. 75%
c. 50%
d. 25%
e. 0%
20. Adult height in humans is at least partially heritable. However, even when environmental
conditions are held constant, humans have an extremely wide variety of heights (not just short,
medium, and tall). What is the best conclusion that can be drawn from this information?
a. Height is probably controlled by one gene with two alleles.
b. Height is probably controlled by one gene with codominant alleles.
c. Height is probably controlled by genes that affect multiple traits.
d. Height is probably controlled by several genes.
21. Which of the following is unique for every individual human (with the exception of identical
twins)?
a. Chromosome number
b. DNA sequence
c. gene sequence
d. protein sequence
e. All of the above
Appendix D (Continued)
22. Rank the following genetic structures in terms of size starting with the largest and
proceeding to the smallest: chromosome, gene, genome, nucleotide.
a. genome, chromosome, gene, nucleotide
b. genome, gene, chromosome, nucleotide
c. chromosome, genome, gene, nucleotide
d. chromosome, nucleotide, genome, gene
e. chromosome, nucleotide, gene, genome
23. Which of the following statements regarding human biology is MOST accurate?
a. The environment determines the expression of human traits.
b. Genes determine the expression of human traits.
c. Genes and the environment determine the expression of human traits.
d. Traits can be determined by the environment or genes, but not both.
Appendix E: Item Analysis
Table A-2. Item analysis for the TBGC. Question numbers refer to items on the Draft 2
(see Appendix D).
Question
P value
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
0.90
0.83
0.59
0.73
0.71
0.78
0.32
0.45
0.73
0.89
0.46
0.78
0.44
0.89
0.63
0.46
0.46
0.51
0.34
0.63
0.59
0.27
0.78
PointBiserial
Correlation
Coefficient
0.41
0.34
0.75
0.60
0.57
0.59
0.29
0.67
0.60
0.25
0.13
0.24
0.54
0.60
0.48
0.26
0.58
0.15
0.06
0.59
0.48
0.57
0.31