Another exception to Mendels rules is polygenic inheritance, which occurs when a trait is controlled by more than one gene. This means that each dominant allele "adds" to the expression of the next dominant allele. Usually, traits are polygenic when there is wide variation in the trait. For example, humans can be many different sizes. Height is a polygenic trait, controlled by at least three genes with six alleles. If you are dominant for all of the alleles for height, then you will be very tall. There is also a wide range of skin color across people. Skin color is also a polygenic trait, as are hair and eye color. Polygenic inheritance often results in a bell shaped curve when you analyze the population ( Figure 1.1). That means that most people fall in the middle of the phenotypic range, such as average height, while very few people are at the extremes, such as very tall or very short. At one end of the curve will be individuals who are recessive for all the alleles (for example, aabbcc); at the other end will be individuals who are dominant for all the alleles (for example, AABBCC). Through the middle of the curve will be individuals who have a combination of dominant and recessive alleles (for example, AaBbCc or AaBBcc).
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phenotypes associated with polygenic traits can be represented by a bell-shaped curve.
--> a. true b. false
polygenic traits demonstrate a wide variation in the phenotype.
--> a. true b. false
if a, b and c represent dominant alleles of a polygenic trait, what genotype will represent an extreme phenotype?
--> a) aabbcc b) aabbcc c) aabbcc d) aabbcc
if a, b and c represent dominant alleles of a polygenic trait, what genotype will represent the moderate (or middle) phenotype?
--> a) aabbcc b) aabbcc c) aabbcc d) all of the above represent moderate phenotypes.
which genotype will have a more extreme phenotype?
a) aabbcc b) aabbcc c) aabbcc --> d) all of the above will show very similar phenotypes.
human height is a polygenic trait. if individuals with more dominant alleles are tall, what will be the genotype of a professional basketball player.
--> a) nnbbaa b) nnbbaa c) nnbbaa d) nnbbaa
in addition to skin color and height, which of the following is also a polygenic trait?
a) freckles --> b) hair color c) eye size d) both (b) and (c)
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