Non-Mendelian traits

Non-Mendelian traits

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​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

Video Sections

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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

In this class, we will 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.

• In our class we will 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