Exceptions to Mendel’s rules :

Mitochondrial DNA codes for proteins and these DNA are inherited only from mother. Both egg and sperm contain mitochondria(mt) as both need them for energy. But after fertilization, sperm mt DNA disappears. So we get all our mt DNA from our mothers, and our mitochondrial defects, too

Jumping Genes or Transposons :

Genetic material is not always stationary was discovered in the 1940s by the plant geneticist Barbara McClintock. Transposons are sequences of DNA that can move around to different positions within the genome of a single cell a process called transposition. In the process they can cause mutations and change the amount of DNA in the genome. Transposons are also called “jumping genes” or “mobile genetic elements”.

Linkage:

If two different genes are located relatively close to each other on the same chromosome, they cannot segregate independently and are usually inherited as a single unit. Genes inherited in this way are said to be linked, and are referred to as “linkage groups”. This is an exception to Mendel’s law of independent assortment.