At this time, we will look at some things about human inheritance and how we study human Inheritance. Obviously, we do not apply Mendelian inheritance crosses to humans, although Pedigrees can be used to determine Mendelian patterns. Let's turn now to some of our human genetic patterns and some examples. We can look at both Mendelian inheritance patterns, and then at some chromosomal alterations which affect human inheritance. Almost every human group anthropologist's study has had prohibitions on marriage between closely related individuals, no double to minimize the expression of more deleterious recessive alleles.
Any mutation has the potential to inhibit the formation of a needed enzyme.
With diploid organisms, however, a mutation most likely affects just one of the homologues, and the second can still code for the appropriate enzyme with little or no phenotypic effect on the individual. This has been demonstrated in laboratory experiments, and is demonstrated with many single gene inheritance patterns when the heterozygous and homozygous dominant phenotypes are indistinguishable. Many of our genetic disorders, which affect metabolism, are the result of the inheritance of recessive alleles that fail to code for the needed enzyme. If this enzyme is critical for survival, affected individuals, those, which are homozygous recessive, will die, if they can not be treated. Hence carriers can pass the allele on to the next generation.