AP Biology : Inheritance

Study concepts, example questions & explanations for AP Biology

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Example Questions

Example Question #1 : Understand Incomplete Dominance

A white homozygous recessive plant is crossed with a homozygous dominant red plant. The plants produced from this cross are all pink. What kind of inheritance does this plant's color follow?

Possible Answers:

Multiple alleles

Sex-linked dominance

Codominance

Incomplete dominance

Complete dominance

Correct answer:

Incomplete dominance

Explanation:

In incomplete dominance, heterozygotes express an intermediate phenotype. Since neither parent expresses the pink phenotype, we know that plant color follows incomplete dominance since neither red nor white is fully expressed as would be the case with complete dominance; rather they are both incompletely expressed.

Example Question #2 : Understand Incomplete Dominance

Which occurs when a heterozygous genotype produces blended traits?

Possible Answers:

Incomplete dominance

Codominance

Monosomy

Trisomy

Pure genotype

Correct answer:

Incomplete dominance

Explanation:

Incomplete dominance involves expression of an intermediate phenotype. The heterozygotes express a phenotype that is a blend of both the dominant and recessive phenotypes. One common example is a flower with white petals and a flower with red petals sexually reproduce to create flowers with pink petals. 

Example Question #3 : Understand Incomplete Dominance

Which of these is an example of polygenic inheritance?

Possible Answers:

Sickle cell anemia

Freckles

Color blindness

Skin color

Duchenne muscular dystrophy 

Correct answer:

Skin color

Explanation:

Polygenetic inheritance is where multiple genes affect a single trait. Human skin color depends on three sets of alleles: Aa, Bb, and Cc. A cross between two parents with any combination of these three alleles determines skin color; there is no single skin color gene.

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