7.2 Complex Patterns of Inheritance

KEY CONCEPT Phenotype is affected by many different factors.

7.2 Complex Patterns of Inheritance

Phenotype can depend on interactions of alleles.

• In incomplete dominance, neither allele is completely dominant nor completely recessive.– Heterozygous phenotype is intermediate

between the two homozygous phenotypes• Heterozygous is like a “blend”

7.2 Complex Patterns of Inheritance

Example: Cross a homozygous red carnation flower (RR) with a homozygous white flower (WW).

• List the genotypes.

4RW

• List the phenotypes.

4 Pink

7.2 Complex Patterns of Inheritance

Example: Cross one heterozygous pink (RW) 4 o’clock flower with a White flower (WW).

• List the genotypes.

2RW, 2WW

• List the phenotypes.

2 Pink, 2White

7.2 Complex Patterns of InheritanceCodominance• Defined: When both alleles

are dominant and equally expressed

• The colors do NOT blend together, but are equally seen

• Ex: Cattle Coat

Red cow x White cow =

Roan Cow

• Ex: Human Blood types

Type A x Type B = Type AB

7.2 Complex Patterns of Inheritance

• Blood types are another example of codominance.

– The ABO blood types result from codominant alleles– This blood group consists of 3 different alleles

• Dominant A allele• Dominant B allele• Recessive O allele

• A and B are equally

dominant

• Many genes have more than two alleles.

7.2 Complex Patterns of Inheritance

Ex: Cross Jason who is homozygous for type A blood with Maria who is homozygous for type B blood.

• List the genotypes.

4AB• List the phenotypes.

4 type AB blood

7.2 Complex Patterns of Inheritance

Ex: Cross Mike who is heterozygous for type A blood with Lisa who is heterozygous for type B blood.

• List the genotypes.1AB, 1Ao, 1Bo, 1oo

• List the phenotypes.1 type AB blood1 type A blood1 type B blood1 type o blood

• Probability of Heterozygous individual?75%

7.2 Complex Patterns of Inheritance

Many genes may interact to produce one trait.

• Polygenic traits are produced by two or more genes.

Order of dominance: brown > green > blue.

7.2 Complex Patterns of Inheritance

• An epistatic gene can interfere with other genes.• This is like a “knock out” gene

7.2 Complex Patterns of Inheritance

The environment interacts with genotype.

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

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

• Phenotype is a combination of genotype and environment.