1. Objectives 11.3 Other Patterns of Inheritance
-Examine the other patterns of inheritance.
-Analyze the relationship between genes and the environment.

2. Beyond Dominant and Recessive Alleles
Despite the importance of Mendel’s work, there are important exceptions to some of his principles.
In most organisms, genetics are more complicated because the majority of genes have more than two alleles.
Mendel’s principles alone cannot predict traits that are controlled by multiple alleles.

3. Incomplete Dominance
In a case where neither allele is dominant it is called incomplete dominance.
In incomplete dominance, the heterozygous phenotype lies somewhere between the two homozygous phenotypes.

4. Codominance
Cases in which the phenotypes produced by both alleles are clearly expressed are called codominance.
For example, in human blood typing both A and B are dominant. If both alleles are present it is expressed as the blood type AB.

5. Multiple Alleles
A gene with more than two alleles is said to have multiple alleles.
Many genes have multiple alleles, including the human genes for blood type.

6. Polygenic Traits
Traits controlled by two or more genes are said to be polygenic traits. Polygenic means “many genes.”
Polygenic traits often show a wide range of phenotypes.
The variety of skin color in humans comes about because more than four different sets of genes control this trait.

7. Genes and the Environment
The characteristics of any organism is not determined solely by the genes that organism inherits.
Genes provide a plan for development, but how that plan unfolds also depends on the environment.

8. True or False
If two speckled chickens are mated, according to the principle of codominance, 25% of the offspring are expected to be speckled. _________________________
For the trait of blood type in humans, there is an allele for Type A, an allele for Type B, and an allele for Type O. Each person inherits one of these alleles from each of their parents, and their blood type is determined by what combination of these alleles they receive. Blood type is inherited as a polygenic trait.

9. Answers
If two speckled chickens are mated, according to the principle of codominance, 25% of the offspring are expected to be speckled. False, 50%
For the trait of blood type in humans, there is an allele for Type A, an allele for Type B, and an allele for Type O. Each person inherits one of these alleles from each of their parents, and their blood type is determined by what combination of these alleles they receive. Blood type is inherited as a polygenic trait. False, trait controlled by multiple alleles