What are patterns of non-mendelian inheritance(besides sex-linked), and why don't they follow the laws?

Some examples:-

1.Polygenic Traits

Some traits are determined by the combined effect of more than one pair of genes.  These are referred to as polygenic , or continuous, traits.  An example of this is human stature.  The combined size of all of the body parts from head to foot determines the height of an individual.  There is an additive effect.  The sizes of all of these body parts are, in turn, determined by numerous genes.  Human skin, hair, and eye color are also polygenic traits because they are influenced by more than one allele at different loci.  The result is the perception of continuous gradation in the expression of these traits.


2.Intermediate Expression

Apparent blending can occur in the phenotype when there is incomplete dominance resulting in an intermediate expression of a trait in heterozygous individuals.  For instance, in primroses, snapdragons, and four-o'clocks, red or white flowers are homozygous while pink ones are heterozygous.  The pink flowers result because the single "red" allele is unable to code for the production of enough red pigment to make the petals dark red.

Another example of an intermediate expression may be the pitch of human male voices.  The lowest and highest pitches apparently are found in men who are homozygous for this trait (AA and aa), while the intermediate range baritones are heterozygous (Aa).  The child-killer disease known as Tay-Sachs  is also characterized by incomplete dominance.  Heterozygous individuals are genetically programmed to produce only 40-60% of the normal amount of an enzyme that prevents the disease.

3.Codominance

For some traits, two alleles can be codominant.   That is to say, both are expressed in heterozygous individuals.  An example of this is people who have an AB blood type for the ABO blood system.  When they are tested, these individuals actually have the characteristics of both type A and type B blood.  Their phenotype is not intermediate between the two.

4.Multiple-allele Series

The ABO blood type system is also an example of a trait that is controlled by more than just a single pair of alleles.  In other words, it is due to a multiple-allele series.  In this case, there are three alleles (A, B, and O), but each individual only inherits two of them (one from each parent).

5.Pleiotropy

A single gene may be responsible for a variety of traits.  This is called pleiotropy .  The complex of symptoms that are collectively referred to as sickle-cell trait , or sickle-cell anemia, is an example.  A single gene results in irregularly shaped red blood cells that painfully block blood vessels, cause poor overall physical development, as well as related heart, lung, kidney, and eye problems.  Another pleiotropic trait is albinism .  The gene for this trait not only results in a deficiency of skin, hair, and eye pigmentation but also causes defects in vision

Aside from sex-linked traits (and the many fine answers in Peter S's answer), LINKAGE is the classic example of non-Mendelian inheritance. In linkage, the genes are inherited in such a way that if the offspring inherits one gene from a particular parent, it will most likely inherit the linked gene from the same parent.

For example, let's say we have two genes S and T. Let's say we look at the cross SSTT x sstt. By Mendilian inheritance, the F1 generation would all show the phenotype ST. The F2 generation would show a mixture of ST, St, sT, and st in the ratio of 9:3:3:1.

However, if the genes for S and T are linked, we would see higher ratios of the parental phenotypes ST and st, and lower ratios of the non-parental phenotypes St and sT in the F2 generation (For example, perhaps 27:3:3:3).

The law that is being violated here is the law of independent assortment, and the reason this happens is because the genes lie on the same chromosome. The only way the genes will assort independently is if crossing over occurs between them during meiosis.