Mendel’s laws discussed previously are only true if
- The genes are carried on the autosomes. The rules do not apply for X-linked or Y-linked traits
- It is a diploid organism that reproduces sexually
- The traits are monogenic i.e determined by one gene
- There is a large number of offspring
- There is no gene interaction, recombination and/or linkage
Exceptions to these rules are:
Incomplete Dominance
Details on incomplete dominance are discussed in detail in the Transmission Genetics: Mendelian Genetics: Introduction and important terms course
Codominance
Details on codominance are discussed in detail in the Transmission Genetics: Mendelian Genetics: Introduction and important terms course
Genetic heterogeneity
This is when the same or very similar phenotypes are produced by different types and location of mutations. It has two components; allelic and locus heterogeneity.
- Allelic heterogeneity is when different mutations in the same loci give rise to the same or similar phenotypes.
Examples