BIOLOGY
Notes for Section 11.3 –
Patterns of Inheritance
Name: _______________________
Date: ____/_____/______
RECESSIVE/DOMINANT GENETIC CROSSES
There are only two traits possible for a trait with one being dominant, the stronger allele that will mask the other allele. The recessive allele is the weaker allele that can only be seen when both the alleles are for the recessive characteristic.
INCOMPLETE DOMINANCE
There are two alleles that are present for a trait. They are both dominant. When they are together, there is a blending of the two genes. The heterozygous phenotype is inbetween the two homozygous phenotypes.
CODOMINANCE
Codominance occurs when both of the alleles are expressed to give a phenotype. An example would be a speckled coat of feathers for a chicken when the allele for white feathers and an allele for black feathers is present. This can also affect the color of the coat for dogs and cats to produce patterns in the fur.
MULTIPLE ALLELES
When there are more than two possible alleles for a trait, then you have multiple alleles.
The genotypes possible for human blood types are multiple alleles. There are different relationships present between these alleles.
 Alleles A and B are codominant alleles that will both express when they are
present together.
 Allele O is a recessive allele that will only be expressed when it is in a
homozygous pairing.
 Rh + and Rh- are dominant/recessive with Rh+ being the dominant allele.
POLYGENIC TRAITS
Sometimes a trait is not affected by only one gene. There can be many genes that work together to give a trait. These are polygenic traits. A polygenetic trait in humans is skin tone. There are so many different variations that are possible due to the different pairing possibilities of MANY genes.
Section 11.3 e-textbook: pages 546 – 552 paper textbook: pages 319 - 322

3]
BIOLOGY
Independent Practice #2 – Genetics
1]
Name: _______________________
Date: ____/_____/______
In humans, there are four types of blood: type A, type B, type AB and type O.
The alleles A and B are codominant to each other. Type O is recessive to both A and B alleles. So a person with genotype AA or AO will have type A blood. a] What possible genotypes will produce type B blood? b] What is the only genotype that will produce type O blood? c] What is the only genotype that will produce type AB blood?
2] b]
If you are type O and you marry a person with type AB, what are the possible outcomes? a] Complete a Punnett square for this cross.
List the possible blood types
[phenotypes] of the offspring. b]
In the 1950’s a young woman sued film star/director Charlie Chaplin for parental support of her illegitimate child. Charlie Chaplin’s blood type was already recorded as type AB. The mover of the child was type A. The son was type O. a] Complete a Punnett square for the cross of the two parents.
The judge ruled in favor of the mother and ordered Charlie Chaplin to pay child support costs of the child. Was the judge correct in his decision based on blood typing evidence? Explain your answer based on the Punnett square results.

6]
5]
BIOLOGY
Independent Practice #2 – Genetics
4]
Name: _______________________
Date: ____/_____/______
Suppose a newborn babies were accidently mixed up in the hospital. In an effort to determine the parents of the baby, the blood types of the baby and two sets of parents were determined.
Baby 1  type O a]
Mrs. Brown
Mrs. Smith


type B
type B
Mr. Brown  type AB
Mr. Smith  type B
Draw a Punnett Squares for each couple. Due to the child having a recessive blood type, please use the genotype BO for Type B blood. b] To which parents does Baby 1 belong? Why? Use your results from the
Punnett squares to explain your answer.
A man with type O blood marries a woman with type AB blood. What are the genotypes and phenotypes possible for their offspring? a] Draw the Punnett square for this couple. b] List the genotype and phenotype possibilities for the offspring.
A man with type B blood marries a woman with type AB blood. a] Draw the Punnett square for this couple. b] List the genotype and phenotype possibilities for the offspring.

BIOLOGY
Independent Practice #2 – Genetics
Name: _______________________
Date: ____/_____/______
7] A geneticist is studying the inheritance of color in flowers when a pure white flower [aabb] is crossed with a dark red flower [AABB]. All of the offspring were pink [AaBa]. Interbreeding of the offspring produced the following data:
Number Phenotype Genotype Fraction % of the whole
43
162
245
166
41 dark red red pink light pink white
What is the clue that this is polygentic inheritance?
Human skin color is a good example of polygentic [multiple gene] inheritance.
Assume that there are only three genes controlling skin color.
Homozygous dominant alleles of [AABBCC] will produce the darkest skin tone because the maximum numbers of particles called melanin are turned on in each skin cell.
Homozygous recessive alleles of [aabbcc] will produce the fairest skin tone because the least numbers of particles called melanin are turned on in each skin cell. If you think about it as numbers of melanin activated by a dominant allele, then AABBCC would have 6 units of melanin turned on in each cell. So the genotypes of AaBbCc would have
3 units of melanin turned on in each cell and will yield a medium skin tone.
8] If a man has the genes AABbCc marries a woman with the genes AaBbCC, what are the possible genotypes?
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How many offspring will have 5 or more units of melanin?
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BIOLOGY
Independent Practice #2 – Genetics
Name: _______________________
Date: ____/_____/______
5
6
7
1
2
3
4
8
# Below Expectations Approaching
Expectations
Meeting
Expectations
Student attempts to answer the question.
1.25
Student partially or incorrectly completes the
Punnett square and has difficulty answering the question.
1.5
Student mostly completes the
Punnett square and has little difficulty answering the question.
2
1.25
1.25
1.25
1.25
1.25
1.25
1.25
1.25
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
2
2
2
2
2
2
2
2
Exceeding
Expectations
Student correctly completes the
Punnett square and
fully answers the question.
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
Not
Attempted