What are the two reasons that there are exceptions to Mendelian heredity?

Incomplete Penetrance. Some genes are incompletely penetrant.

Sex-limited genes are ones that are inherited by both men and women but are normally only expressed in the phenotype of one of them. The heavy male beard is an example.

Pleiotropy. A single gene may be responsible for a variety of traits.

Stuttering Alleles.

Explanation:

desert perennials often survive by remaining dormant during dry periods of the year, then springing to life when water becomes available. most annual desert plants germinate only after heavy seasonal rain, then complete their reproductive cycle very quickly.

many other transport proteins, often called pumps, move materials against a concentration gradient. active transport drives molecules across a membrane from a region of lower concentration to a region of higher concentration. this process, shown in figure 5.1, uses transport proteins powered by chemi- cal energy.