Mendel is the father of genetics, who established the basic laws for inheritance, these are summarized as Mendel’s Law of Segregation and Mendel’s Law of Independent Assortment.
Mendel’s Law of Segregation
There are two alleles for each gene; during the gamete formation, the two alleles of one gene segregate from each other independently.
Mendel’s Law of Independent Assortment
During the gamete formation, genes from different chromosomes assort independently and combine randomly
Extensions to Mendel’s Laws
Most of nuclear genes follow Mendel’s Laws. However, there are sometimes exceptions. For instance, if genes are within certain distance on same chromosomes, they do not follow the Law of independent assortment, instead they are linked when transmitted to next generation. Genes that are located in the cytoplasm do not follow either Mendel’s Laws, they exhibit maternal inheritance trait. If the dominance is incomplete, a dominant trait wouldn’t be observed immediately and they become co-dominant, meaning both alleles will show phenotype.
Statistics plays an important role in genetics because counting is a base for both classical genetics and population genetics. For model-fitting test, chi square test is often used.
Human pedigree is very useful in analysis of genetic diseases, it is often used to determine whether a trait is dominant or recessive, sex-linked or autosomal.