Download Multiple Alleles

BIOLOGY 1
STANDARD 4.0
LESSON 4.7
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Genetics and Biotechnology
The student will investigate the concepts of genetics and heredity,
different methods of reproduction, patterns of inheritance, and
genetic disorders; as well as, explore and evaluate the DNA
technologies from both a scientific and ethical perspective.
Lesson 8- Examine modes of inheritance involving incomplete dominance
Co-dominance and multiple alleles
Interact with the Incomplete Dominance and Codominance Tutorial
in Lubey's BioHELP to see how genetic problems of this nature can be solved.
After going through the tutorial complete the following worksheet.
Incomplete Dominance
An exception to Mendel's Law of Dominance is the situation where a dominant
allele does not always show its characteristic. If one were to mate a homozygous
red four o'clock flower with a homozygous white four o'clock flower one would
expect all the F1 offspring would be red, since red is dominant to white. The
same would go for a farmer wanting to mate a red bull to a white cow. He would
expect all the calves to come out red. This does not happen since the dominant
allele is responsible for pigment production while the recessive white allele does
not allow pigment to be produced.
If we take a red four o'clock and mate it with a white one, all the offspring would
be pink.
Gametes ----->
R
R
Rr
Rr
Rr
Rr
|
r
r
The Rr genotype represents an organism containing 1/2 of the pigment needed
to become red. So the individual gives off a pink color. The same thing occurs in
the cattle. The recessive allele does not allow pigment to be produced. In this
case the calves come out spotted. They are called roan. Pink flowers and roan
cattle are hybrid and cannot breed true.
Mate two pink four o'clock in the space below. Then answer the questions that
follow.
Parent Genotypes: _________________ X _________________
Gametes ----->
R
R
Rr
Rr
Rr
Rr
|
r
r
1. What are the phenotypes of the offspring?
______________________________________________
2. List the genotypes of the offspring.
___________________________________________________
3. What is the genotypic ratio? _______________________________________.
4. What is another name for a heterozygous red offspring?
________________________________.
Co-dominance
(Courtesy: Prentice Hall Science Explorer, Cells and Heredity, 2000)
For some alleles, an inheritance pattern called co-dominance exists. In codominance, the alleles are neither dominant nor recessive. As a result neither
allele is masked in the offspring. In Erminette chickens, the alleles for black
feathers and white feathers are co-dominant. When a chicken homozygous for
black feathers is crossed with a chicken homozygous for white feathers, the
heterozygous offspring will have both black and white feathers.
Multiple Alleles
(Courtesy: Prentice Hall Science Explorer, Cells and Heredity, 2000)
Some human traits are controlled by a single gene pair that has more than
two alleles. Such a gene is said to have multiple alleles - three or more forms of
a gene that code for a single trait. You can think of multiple alleles as being
flavors of pudding. Pudding usually comes in more flavors than just chocolate
and vanilla!
Even though a gene may have multiple alleles, a person can carry only two of
those alleles. This is because chromosomes exist in pairs. Each chromosome in
a pair carries only one allele for each gene.
One human trait that is controlled by a gene with multiple alleles is blood
type. Proceed to the Multiple Alleles Tutorial in Lubey's BioHELP to learn about
the inheritance of human blood groups.
Multiple Alleles
Another exception to Mendel's laws is the presence of more than two alleles for a
particular trait. One example of this is human blood type. There are four basic
human blood types: A, B, AB, and O. Based on this observation one can see that
A and B type blood are co-dominant and O is the recessive allele, The genotypes
for these blood types are found below.
Blood Type
(Phenotype)
A
B
AB
O
Genotypes
AA and
AO
BB and
BO
AB
OO
Who can donate blood to whom.
Blood
Type
A
B
AB
O
Can Receive
from
A and O
B and O
A, B, AB, and O
O
What will happen if a person receives the wrong blood type during transfusion?
a). The protein on the red blood cell will react with the antibody in the plasma of
the donor's blood.
b). This reaction will cause the blood cells to join together and form clumps.
c). These clumps will block small arteries and veins throughout the body, causing
a heart attack, stroke, or blockage in other vital organs.
1. What blood type is considered the universal donor?
__________________________.
2. What blood type is considered the universal recipient?
__________________________.
Genetic problems:
3. Mary has type O blood and her husband Joseph has type A blood. What are
the chances of their having a child with type O blood? Joseph is heterozygous A.
why must we know the genotype of Joseph?
________________________________________________________________
Work the Punnett square in the space below.
4. Mr. and Mrs. Roe had a child with type A blood. In the same hospital Mr. and
Mrs. Doe had a child with type O blood. A week after they took their children
home, the Roe's believed the baby they took was not theirs. They went to the
hospital and had their blood types checked along with the Does. The results were
as follows.
Doe's Blood
Types
Mr. Doe : O
Mrs. Doe : AB
Roe's Blood
Types
Mr. Roe : A
Mrs. Roe : O
Work out he Punnett squares in the space below:
Do the Roe's have the correct child? Explain
_________________________________________________
Use the following link to learn about Human blood types which is an
example of Co-dominance and multiple allele genetic traits
Tutorial on blood type
When you get to the bottom of the tutorial page click “go on” the following
lessons and practice problems
- Human ABO markers
- blood types and genotypes
- How alleles are inherited
- Blood type problem set