Name ____________________________ Genetics for Honors Chem Sophs
Genetics for Honors Chem Sophs
Use the information to answer the next four questions
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, that person is a carrier.
The pedigree below represents a family in which some members have the sickle cell allele.
1. 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 %
C. 75 %
D. 100 %
2. Draw a Punnett square or comparable diagram for the couple in the first generation of
the pedigree. Use B to represent the allele for normal red blood cells and b to represent
the allele for sickle cell disease. How do the couple’s actual children compare to the
expected results shown in your Punnett square? Respond in the space provided in your
Answer Document. (4 points)
3. Although sickle cell disease has negative effects on those who suffer from it, the allele is
widespread in many parts of the world. This is because in areas where malaria is a
significant danger, the sickle cell allele
ceases to cause symptoms.
attacks the parasite that causes malaria.
spreads rapidly in people weakened by malaria.
conveys a health advantage to those who carry the allele.
4. Which person on the pedigree could not pass the allele for sickle cell disease to his/her
5. A characteristic of pea plants is the color of the pod holding the seeds. Pea plants only
have yellow pods when they possess two recessive genes (gg). A heterozygous
genotype produces a plant with green pods. Which of the following Punnett squares
shows the correct results of a cross between two heterozygous plants?
6. Which statement describes the work of Gregor Mendel?
A. He developed basic principles of heredity without having knowledge of
B. He explained the principle of dominance on the basis of the gene-chromosome
C. He developed the microscope for the study of genes in pea plants.
D. He used his knowledge of gene mutations to explain the appearance of new traits in
7. In canaries, the gene for singing (S) is dominant over the gene for non-singing (s). When
heterozygous singing canaries (Ss) are mated with non-singing canaries, what
percentage of their offspring is likely to possess the singing trait?
8. In humans, the gene for polydactyly (extra fingers or toes) is dominant over the gene for
the normal number of digits. If parents who are both homozygous dominant for
polydactyly (PP) have four children, how many of the children will probably have extra
fingers or toes?
9. In a certain breed of cats, having black hair is the result of two dominant alleles for hair
color (HH). The heterozygous genotype (Hh) produces a cat that has black and white
spots. Having two recessive (hh) genes results in a white haired cat. The Punnett square
below shows the results of a cross between which two cats?
H HH HH
h Hh Hh
two black cats
a spotted cat and a white cat
a black cat and a spotted cat
two spotted cat