Ohio Graduation Test for Science– March 2005
Annotated Item 11
Standard and Benchmark Assessed:
Standard:
Benchmark:
Life Sciences
C. Explain the genetic mechanisms and molecular basis of inheritance.
Multiple Choice Question:
Sickle cell Disease
Sickle cell disease is a group of inherited disorders in which deoxygenated red blood cells
become distorted and take on a shape like a sickle. There are two common alleles for this gene.
One causes normally shaped red blood cells and the other allele causes the red blood cells to
have a sickle shape. The sickled cells can lodge in the smallest blood vessels and reduce the
circulation of blood to tissues.
The sickle cell allele is most common in areas where the disease malaria is a significant
problem, and among people whose ancestors are from those areas. Evidence shows that
having just one sickle cell allele makes a person resistant to malaria.
This genetic condition is a recessive trait. When an individual has only one allele for the sickle
cell trait, the person is a carrier.
The pedigree below represents a family in which some members have the sickle cell allele.
11.
In the genetic pedigree, person U and her husband are considering having another child.
What is the percent chance that this child will develop sickle cell disease?
A.
25%
B.
50%
C. 75%
D. 100%
Commentary:
This multiple choice question asks students to analyze the genetic pedigree to determine the
probability of person U and her husband having a child that will develop sickle cell disease.
Source: Ohio Department of Education
July 05
Ohio Graduation Test for Science– March 2005
Annotated Item 11
Students must use the key to determine that person U is a carrier female who is heterozygous
for the sickle cell trait. One of her alleles for red blood cell shape is normal and the other is
sickle cell shape. Her husband is also a carrier for the sickle cell trait. He has one allele for
normal red blood cell shape and one allele for sickle cell shape. Below is the Punnett square
showing the allele combination of the offspring that these two people can produce.
B
b
B
BB
Bb
b
Bb
bb
This Punnett square illustrates that there is a 25% chance that a child could receive two alleles
for normal red blood cell shape. There is a 50% chance that the child could receive one allele
for the sickle cell shape therefore carrying the sickle cell trait. There is a 25% chance that the
child could receive two alleles for sickle cell shape. Answer choice A is correct because
individuals with two alleles for sickle cell shape will develop sickle cell disease. Answer choices
B, C and D are incorrect because they are inaccurate interpretations of the Punnett square.
This question is classified as Communicating Understanding / Analyzing Science Information
because the task requires students to interpret a pedigree to determine the genotypes of
parents. Once the genotype of the parents is determined the student needs to be able to
determine the probability of an offspring developing sickle cell disease.
Performance Data:
The percent of public school students selecting answer choice A for question 11 on the March
2005 Ohio Graduation Test was 34%.
Keywords:
genetics, Punnett square, pedigree, sickle cell disease, malaria
Source: Ohio Department of Education
July 05