Genetics Worksheet 2: Incomplete and Co-dominance
Name:
Directions: To answer the following questions about Incomplete and Co-dominance, you will need a
scratch piece of paper and your PowerPoint notes about how to appropriately represent the alleles for
these different patterns of inheritance.
Incomplete Dominance:
1. Define incomplete dominance.
a. The first type of inheritance we discussed, complete or simple dominance, states that the
phenotype for the heterozygous individual is the same as the phenotype for the homozygous
dominant individual. How does incomplete dominance affect the phenotype of the
heterozygous individuals?
b. In the example in your PowerPoint notes, a red flower and a white flower will make a pink
flower. What is the genotype of the heterozygous pink flower?
c. Fill out the following Punnett Square showing the possible offspring of two heterozygous pink
flowers.
R
R’
R
R’
d. What is the phenotypic ratio of the F2 generation.
:
:
Co-dominance:
2. Define Co-dominance?
a. The first type of inheritance we discussed, complete or simple dominance, states that the
phenotype for the heterozygous individual is the same as the phenotype for the homozygous
dominant individual. How does co-dominance affect the phenotype of the heterozygous
individuals?
b. In the example in your PowerPoint notes, a red flower and a white flower will make a striped
flower. What is the genotype of the heterozygous striped flower?
c. Fill out the following Punnett Square showing the possible offspring of two heterozygous
striped flowers.
FR
Fw
FR
FW
d. What is the phenotypic ratio of the F2 generation?
:
:
Genetic Problems for Incomplete and Co-dominance
3. Sickle Cell Anemia is a genetically inherited condition caused by an incorrect amino acid in the
hemoglobin protein.
Table 1: Genotype and Phenotype of Homozygous and Heterozygous Individuals
Description of Phenotype
Photograph of Phenotype
Genotype
An individual who is homozygous to sickle cell
anemia produces all C (or sickle) shaped red
blood cells because of the incorrect
hemoglobin. These individuals need medical
treatment to survive into adulthood.
HSHS
Heterozygous individuals produce half normal
red blood cells and half C shaped red blood
cells and can survive into adulthood and have
children. These individuals are called carriers
because they are unaffected and can pass the
sickle cell disease on to their children.
HSHN
Individuals without the disorder are
homozygous and produce red blood cells that
are all round.
HNHN
a. What type of inheritance (incomplete or co-dominance) does sickle cell anemia display?
b. What are the genotypes of carrier parents who have a homozygous child with sickle cell
anemia? NOTE: Carriers of a disease possess the allele for the disease but do not have it.
and
c. Use a Punnett Square to show your answer.
d. What is the percentage chance that they would have another child who would be homozygous
for sickle cell anemia?
4. In Andelusian fowl, a single pair of alleles controls the color of the feathers. Three colors of birds
are observed: black, splashed white and blue (really grey in appearance). A farmer carriers out the
crosses seen in Table 2 below to determine how she can guarantee the sale of only blue fowl.
Black and Speckled white parents
Blue (grey) offspring
Table 2: Parents and offspring from the crosses a farmer performed to determine how to sell only blue
fowl.
Parents
Offspring
Black x splashed white
Blue
Black x black
Black
Black x blue
Blue and black (1:1)
Blue x splashed white
Blue and splashed white (1:1)
Splashed white and splashed white
Splashed white
a. What type of gene inheritance pattern (incomplete or co-dominance) is displayed by blue
feather color?
b. What are the genotypes for these three phenotypes?
Black:
White:
Blue:
c. Use a Punnett Square to show a cross between two blue fowl.
d. What are the phenotypic ratio of the offspring (be sure to write out the fractions and
phenotypes)?
:
:
a. If you wanted to sell eggs, all of which would yield blue fowl, which birds would you breed?
4. Roan is a color of cattle in which both red and white hairs are present. If you bred a white cow with
a red cow the offspring will all be roan.
Cow Coat
color
Phenotype Red Coat
Roan Coat
White Coat
Genotype
a. Use a Punnett Square to show the possible offspring produced by a roan bull and a red cow.
What is the phenotypic ratio of the offspring produced?
:
b. Use a Punnett Square to show the possible offspring produced by a Roan bull and a Roan cow.
What is the phenotypic ratio of the offspring produced?
:
:
c. Use a Punnett Square to show the possible offspring produced by a Red bull and a White cow.
What is the phenotypic ratio of the offspring produced?
5. A researcher wants to determine how the color of Snapdragon
flowers is inherited: by complete or simple dominance, codominance, or incomplete dominance. She found the following three
colors in nature. Explain how she could design an experiment to
show how the color is inherited.
Use a Punnett Square to clarify your answer above.
Bibliography
“Blood smear illustrating sickle cell anaemia. Stained with Giemsa. Note the distinctive "sickle" shape,
and "target cells" with concentric rings of red stain.” by Keith Chambers. Scooter Project
http://www.sicklecellanaemia.org/teaching-resources/resources/scooter44-63/scooter44.html.
Licensed under CC BY-SA 3.0 via Wikimedia Commons “Andlusian fowl” by maralpz2006. Blue Andalusian thread! Backyard Chickens.
http://www.backyardchickens.com/t/290822/blue-andalusian-thread/50
“Roosters and Chickens” by Annette Mickelson. News from Oak Creek Ranch.
http://aspenmeadows.blogspot.com/2014/06/roosters-and-chicken-names.html
“Some Red and Roan Cattle” by Nesikep.
http://www.cattletoday.com/forum/viewtopic.php?f=5&t=53157