11.3: Other Patterns of Inheritance Not all types of inheritance are as simple as those studied by Mendel. We can still figure out possible genotypes and phenotypes using Punnett squares, but the rules are slightly different. For BOTH parents, use the first letter of the trait being crossed and make it a capital letter – will be different letters this time!

Incomplete Dominance In some organisms, an individual displays a trait that is intermediate between the two parents, a condition known as incomplete dominance. Neither trait totally covers over the other – it’s a mix (blending) of both traits. This is very common in plants.

crossing red flowers with white flowers will produce pink flowers WW RW RR

Codominance For some traits, two dominant alleles are expressed at the same time. Both forms of the trait are expressed at the same time – this is called codominance. Codominance is different from incomplete dominance because both traits are displayed.

crossing red flowers with white flowers will produce red AND white flowers

crossing red cows with white cows will produce roan – red cows with white blotches

Multiple Allele Traits Some genes have three or more alleles and are said to have multiple alleles. Even for traits controlled by genes with multiple alleles, an individual can have only two of the possible alleles for that gene – one from Mom and one from Dad!

Blood types of offspring There are three different alleles for human blood type: IA (A), IB (B), and i (O). Since there are three different alleles, there are a total of six different genotypes. Allele from Parent 1 Allele from Parent 2 Genotype of offspring Blood types of offspring A AA B AB* AB O AO BB BO OO

Polygenic Traits When several genes influence a trait, the trait is said to be a polygenic trait. The genes for a polygenic trait may be scattered along the same chromosome or located on different chromosomes. Familiar examples of polygenic traits in humans include eye color, height, weight, & hair and skin color.

Genes and the Environment The phenotype of an organism depends on the interaction of genes with the environment. One example is the case of temperature-sensitive mutations. In a high temperature environment, where molecules are moving more quickly and hitting each other, this results in the protein losing its structure and failing to function. In a low temperature environment, however, the protein's structure is stable, and it functions normally.

This type of mutation is visible in the coat coloration of Siamese cats – a mutation in an enzyme responsible for pigment production causes it lose function at high temperatures. The protein remains functional in areas of skin that are colder —legs, ears, tail, and face — so the cat has dark fur at its extremities.