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Chapter 20: Problem 10

Define and give an example of each of the following inheritance patterns: polygenic inheritance, multifactorial trait, incomplete dominance, codominance, and multiple alleles. (pages \(479-81)\)

Short Answer

Expert verified
Polygenic inheritance is when a trait is controlled by multiple genes, such as human skin color. A multifactorial trait is determined by genetic and environmental factors, like height in humans. Incomplete dominance results in a blend of traits, seen in pink snapdragon flowers (Rr). Codominance has both traits fully expressed, as in the AB blood type. Multiple alleles involve more than two possible alleles for a gene within a population, exemplified by the ABO blood group system.

Step by step solution

01

Polygenic Inheritance

Polygenic inheritance refers to the inheritance pattern in which a particular trait is controlled by multiple genes, each having a small effect on the overall phenotype. In other words, the genetic information for a certain characteristic is determined by more than one gene. Example: Human skin color is a classic example of a polygenic trait. It is influenced by several genes, and the various combinations of these genes determine the wide range of skin colors in humans.
02

Multifactorial Trait

A multifactorial trait is a characteristic that is determined by multiple genetic factors as well as environmental factors. Such traits result from the combined effect of genes and non-genetic factors. Example: Height in humans is a multifactorial trait, as it is influenced by various genes as well as environmental factors such as nutrition.
03

Incomplete Dominance

Incomplete dominance, also known as partial dominance, is a type of non-Mendelian inheritance pattern in which the phenotype of the heterozygous individual is intermediate between those of the two homozygous parents. Neither allele is completely dominant over the other, resulting in a blend of both traits. Example: In snapdragon flowers, there are two alleles for flower color: one for red (R) and one for white (r). When these two alleles are combined in a heterozygous individual (Rr), the flower color is pink, which is intermediate between red and white.
04

Codominance

Codominance refers to the inheritance pattern in which both alleles in a heterozygous individual are fully expressed, and neither is dominant over the other. As a result, the offspring display a mix of both parental phenotypes instead of a blend. Example: The AB blood type in humans is a result of codominance. When a person inherits the A allele from one parent and the B allele from the other, both alleles are fully expressed, resulting in the AB blood type.
05

Multiple Alleles

Multiple alleles refer to the presence of more than two possible alleles for a specific gene within a population. While any individual can only carry two alleles for a gene, there can be a larger number of alleles present in the total population. Example: The ABO blood group system in humans is an example of multiple alleles. There are three different alleles for the gene that determines blood type: A, B, and O. While any individual can only inherit two of these alleles (one from each parent), all three can be found within the population.

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Most popular questions from this chapter

The genotype of an individual with the dominant phenotype can be determined best by reproduction with a. the recessive genotype or phenotype. b. a heterozygote. c. the dominant phenotype. d. the homozygous dominant. e. Both a and b are correct.

Using a pedigree, show an autosomal recessive disorder pattern and an autosomal dominant disorder pattern. (pages \(474-75\) )

What is the chance that a dihybrid cross will produce a homozygous recessive in both traits? a. \(9 / 16\) b. \(1 / 4\) c. \(1 / 16\) d. \(3 / 16\) e. \(1 / 8\)

In humans, pointed eyebrows \((P)\) are dominant over smooth eyebrows ( \(p\) ). Mary's father has pointed eyebrows, but she and her mother have smooth. What is the genotype of the father? a. \(p p\) b. \(P p\) c. \(P P p p\) d. \(p P p P\)

Under what condition(s) will an autosomal recessive disorder appear? a. inheritance of a single recessive allele b. inheritance of one dominant and one recessive allele c. inheritance of two recessive alleles d. Both a and c are correct.
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