Other Patterns of Inheritance

Non-Mendelian traits

​Non-Mendelian Traits

​Non-Mendelian traits are traits that don't follow the basic rules of dominance and recessiveness that you have learned about so far. This includes:

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• ​Multiple alleles

• Incomplete dominance

• Co-dominance

• Polygenic traits

• Epistasis

Multiple Choice

Traits that break the rules by having no clearly dominant allele are

• Non-Mendelian

• Non-Newtonian

• non-hereditary

Incomplete dominance

Incomplete dominance leads to an "in between" phenotype.

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​Think of incomplete dominance as two phenotypes meeting each other in the middle; a compromise.

Incomplete Dominance

We use all capital letters to indicate incompletely dominant alleles.

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In this example, the red is incompletely dominant over white, so flowers with genotype RW have the phenotype pink.

Multiple Choice

Pink color in snapdragon flowers are a result of

• incomplete dominance of red and white alleles

• a missing allele

• codominance of pink and red alleles

Codominance

• ​Think of codominance as two alleles sharing space; both phenotypes are partially seen.

• We indicate codominance by using capital letters for all traits, for example, codominant red and white color will be written RW

• Roan color in animals such as horses and cows is a result of codominance of red and white

Roan color

This cow has genotype RW because she has a red gene and a white gene, and the alleles are codominant.

Roan color

This horse has genotype RW because it has a red gene and a white gene, and the alleles are codominant.

Multiple Choice

When two traits are equally dominant, we call this

• incomplete dominance

• independent dominance

• codominance

Example: Skin tone is a polygenic trait.

At least 150 genes contribute to skin tone. Scientists are still studying this.

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​Polygenic: 2 or more genes contribute to a trait.

Multiple Choice

A trait determined by many genes is

• photogenic

• polygenic

Multiple Select

Human traits that are polygenic include (check all that apply)

• a cleft chin

• height

• skin tone

• widow's peak hairline

Examples: Scientists are still researching the genetics of diabetes in humans. It is believed that at least 4 chromosomes have genes for diabetes.

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Note: Environmental factors can also affect diabetes (and other genetic conditions.)

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​Epistasis: When 2 or more genes interact and a trait is suppressed.

Multiple Choice

Epistasis is when

• an organism is missing a gene

• an organism has extra genes

• one gene depends on another gene to be expressed

Multiple Choice

In a species of goat, white and brown are codominant. One parent is solid white and the other parent is solid brown. What is the predicted phenotype of their offspring? Sketch a Punnett square to find the answer.

• 25% white, 25% brown, 50% white & brown

• 50% white, 50% brown

• 100% white & brown

Multiple alleles

• A gene that is controlled by more than two alleles.

• Ex) ABO blood type. Blood type is controlled by three alleles. Each individual will have just two alleles of the three.

Multiples Alleles

• 3 or more alleles to choose from

• each trait only contains 2 alleles

• one allele from dad

• one allele from mom

ABO blood group is an example of multiple alleles, complete dominance, and co-dominance inheritance.

Multiple Choice

Mama Isabella has a blood type of O. Her son, Norman, has also a blood type of O. What is the blood type of Norman's father?

• A

• B

• AB

• O

Multiple Choice

The two cows on the top are the parents and the cow on the bottom is the offspring. What is the type of inheritance pattern is being exhibited?

• Incomplete Dominance

• Codominance

• Multiple Alleles

• Polygenic Inheritance

Multiple Choice

What type of inheritance pattern does the diagram represent?

• Incomplete Dominance

• Codominance

• Multiple Alleles

• Polygenic Inheritance

Multiple Choice

In humans, the gene for curly hair (H) is incompletely dominant to the gene for straight hair (h). Individuals that are heterozygous (Hh) have wavy hair.

Two wavy-haired heterozygous parents have a child.

What is the likeliness that the child will have wavy hair?

• 1/4

• 1/2

• 3/4

• 4/4