Download Sickle Cell Inheritance

Name ________________________________ Class _______ Date _________________
Sickle Cell Inheritance
Use the virtual Genetics lab room to
determine the pattern of inheritance of sickle
cell disease.
Lab Bench Used
Sickle cell disease, also called sickle cell anemia, is a common genetic disorder.
About 1 in 12 Americans of African heritage carry the allele for sickle cell. This
allele is expressed in hemoglobin, the molecule that carries oxygen in red blood cells.
In people with the disease, hemoglobin molecules clump together in long fibers,
forcing the red blood cells, which are normally round, into long shapes that look like
sickles. These sickle-shaped cells tend to get stuck in capillaries, slowing the
distribution of oxygen to tissues and organs. Pain and fatigue are common symptoms,
and organ failure can occur as well.
A related condition called sickle cell trait has few if any harmful symptoms. People
who have this trait actually have a heightened resistance to malaria, an infectious
disease that has killed millions of humans, particularly in tropical areas where
mosquitoes, which carry the disease, are abundant.
In this lab activity, you will act as a genetics counselor. Using the virtual Genetics
lab, you will determine how likely different sets of parents are to have children who
will suffer from sickle cell disease.
Enter the Virtual Bio Lab and select the title of this lab activity from the “Heredity”
menu on the whiteboard. You will be taken to the virtual Genetics lab room.
Part A: Finding the Pattern of Inheritance
In the virtual Genetics lab, choose “Human” from the Species Selector and “SickleCell Anemia” from the menu of traits. Suppose a husband and wife come into your
office. The husband is homozygous for the sickle cell allele, which means he suffers
from sickle cell disease. The wife is homozygous for the normal allele. They wish to
have children but are concerned about passing on sickle cell anemia.
Set the parents’ alleles accordingly and set the number of offspring to the
maximum of 6. Click the “Cross” button repeatedly until you can see the results for
100 offspring—a large enough sample size to determine the pattern of inheritance of
the trait. Make sure the “Include Male/Female” box in the lower left corner of the
results box isn’t checked.
1. What percentage of the F1 offspring has sickle cell trait, sickle cell anemia, and
normal blood?
______________________________________________________________________
______________________________________________________________________
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
Virtual Bio Lab
1
Heredity:
Sickle Cell Inheritance
Name ________________________________ Class _______ Date _________________
2. What does this result suggest about the pattern of inheritance of sickle cell
disease?
______________________________________________________________________
______________________________________________________________________
______________________________________________________________________
_____________________________________________________________________________
3. How would you counsel this particular couple about their would-be offspring?
What about their offspring’s offspring?
______________________________________________________________________
______________________________________________________________________
______________________________________________________________________
_____________________________________________________________________________
4. Complete the three Punnett squares below to illustrate how likely this couple’s
children are to produce offspring with sickle cell trait or disease. (A represents the
normal allele; S represents the sickle cell allele.) Use the virtual Genetics lab to
run these crosses and confirm the accuracy of your Punnett squares. To the right
of each square, give the percentages of offspring that will be normal, carriers
(sickle cell trait), and sufferers of sickle cell disease.
Homozygous normal
Scenario 1
A
Heterozygous
(carrier)
A
Percentage normal offspring:
Percentage with sickle cell trait
(carriers):
A
Percentage with sickle cell disease:
S
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
Virtual Bio Lab
2
Heredity:
Sickle Cell Inheritance
Name ________________________________ Class _______ Date _________________
Heterozygous (carrier)
Scenario 2
A
Heterozygous
(carrier)
Percentage normal offspring:
A
Percentage with sickle cell trait
(carriers):
S
Percentage with sickle cell disease:
Homozygous for sickle cell
allele
Scenario 3
S
Heterozygous
(carrier)
S
S
Percentage normal offspring:
A
Percentage with sickle cell trait
(carriers):
S
Percentage with sickle cell disease:
Part B: Evolution and the Sickle Cell
5. It’s harmful to have two sickle cell alleles, but in a region where malaria is
prevalent, having one sickle cell allele can be beneficial. Look at the phenotype
breakdown of the offspring in each of the three scenarios above. Which phenotype
is most common overall?
______________________________________________________________________
______________________________________________________________________
_____________________________________________________________________________
6. Explain how a population in a region affected by malaria could derive more
benefit than harm from the presence of the sickle cell allele.
______________________________________________________________________
______________________________________________________________________
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
Virtual Bio Lab
3
Heredity:
Sickle Cell Inheritance
Name ________________________________ Class _______ Date _________________
_____________________________________________________________________________
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
Virtual Bio Lab
4
Heredity:
Sickle Cell Inheritance