7.2 Complex Patterns of Inheritance

Section 7-2: “Complex Inheritance”

1) Incomplete Dominance

2) Co-Dominance

3) Multiple Alleles

4) Polygenic Traits

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7.2 Complex Patterns of Inheritance

KEY CONCEPT Many phenotypes are not explained by the Mendel’s “simple” dominance.

7.2 Complex Patterns of Inheritance

Phenotype can depend on interactions of alleles.

1) In Incomplete Dominance, neither allele is completely dominant nor completely recessive.

– The heterozygous phenotype is intermediate between the two homozygous phenotypes

– The homozygous parental phenotypes are not seen in F1 offspring. (There are 3 phenotypes.)

7.2 Complex Patterns of Inheritance

Example: Incomplete Dominance: 4 O’Clock Flowers

The parents’ genotypes are purebred (homozygous) and are red & white, but the offspring’s phenotypes are neither red nor white.

The F1 generation’s genotypes are all hybrid (heterozygous), buttheir phenotype is pink, a mix or “intermediate” phenotype.

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7.2 Complex Patterns of Inheritance

2) In Codominance, both alleles will be completely expressed to produce a third genotype showing both phenotypes.

– Codominant alleles are neither dominant nor recessive.– Ex: Roan Cattle; and the A-B-O blood types result from

codominant alleles.

Blood Types A and B are CodominantRoan Cattle

7.2 Complex Patterns of Inheritance

Example of Codominance: Blood Type

- There are 3 alleles: A, B, and O- A and B are codominant- O is recessive to A and B- How many genotypes and phenotypes does this make?

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7.2 Complex Patterns of Inheritance

Multiple Alleles

• Many genes have more than two alleles (“multiple alleles”)

- Blood Type: A, B, & O alleles

7.2 Complex Patterns of Inheritance

Many genes may interact to produce one trait.

3) Polygenic traits are produced by two or more genes acting together.

Ex: Eye color (3 genes)

Order of dominance: brown > green > blue.

7.2 Complex Patterns of Inheritance

• Epistatic Genes: an “epistatic” gene can interfere with other genes.

- One or more genes can affect the expression of other genes

7.2 Complex Patterns of Inheritance

The environment interacts with genotype.

• Height is an example of a phenotype strongly affected by the environment

- nutrition, diseases

• The sex of sea turtles depends on both genes and the environment

• Phenotype is a combination of genotype and environment.