SImple Inheritance Patterns

When a dominant phenotype is not expressed even though the individual carries the dominant allele

Protein coded by the gene may not exert an effect, due to environmental influences or other genes that counteract the protein

When a heterozygote has a phenotype that is intermediate between either corresponding homozygote

50% of the protein, produced by a single copy of the functional allele in the heterozygote, is not sufficient to produce the same trait as in a homozygote making 100% of that protein.

When the heterozygote has a trait that confers a greater level of reproductive success than either homozygote

1. Cells may have increased resistance to infection by microorganisms

2. They may produce more forms of protein dimers with enhanced function

3. They may produce proteins that function under a wider range of conditions

Example: Sickle Cell Anemia

When heterozygote expresses both alleles simultaneously without forming an intermediate phenotype

The codominant alleles code proteins that function slightly differently from each other, and the function of each protein in the heterozygote affects the phenotype uniquely

The inheritance of genes that are located on the X chromosome

If a pair of X-linked alleles shows a simple dominant/recessive relationship, 50% of the protein, produced by a single copy of the dominant allele in a heterozygous female, is sufficient to produce the dominant trait. Males have only one copy of X-linked genes and therefore express the copy they carry.

The effect of sex on the phenotype of an individual

Sex hormones regulate gene expression, which influences phenotype

The trait only occurs in one sex

Sex hormones regulate gene expression, which influences phenotype. In this case, sex hormones only produces in one sex are essential for an individual to display a phenotype

Allele that has the potential to kill the individual

Most commonly loss-of-function alleles that code proteins necessary for survival