Modes of inheritance can not be studied in humans through controlled matings. Commonly, geneticists use pedigree analysis to infer the mode of inheritance in humans. The ultimate source of all genetic variation is mutation. Genetic recombination involves the mixing of alleles such that the alleles of different genes are brought together in different combinations. Meiosis is the primary vehicle for recombination operating through independent assortment and crossing over.
Variation is necessary for understanding patterns in inheritance.
Recombination is any process in a meiocyte that generates a haploid product of meiosis with a genotype differing from both haploid genotypes that originally combined to form the diploid meiocyte. The product of meiosis so generated is called a recombinant. A tester is an individual who is homozygous recessive for the genes studied. The probability of the simultaneous occurrence of two independent events is equal to the product of their individual probabilities. The probability of the occurrence of any of a set of mutually exclusive events is equal to the sum of the probabilities of the events.