Inheritance is the passage of hereditary traits from one generation to the next. Genetics is the study of inheritance. Humans have 23 pairs of homologous chromosomes; one in each pair from the father and one from the mother. Genes for the same trait that are in the same location on each homologue are alleles. A mutation is a permanent heritable change in an allele.
One genetic disorder caused by a mutation is phenylketonuria (PKU). People with PKU cannot make the enzyme phenylalanine hydroxylase which is needed to break down phenylalanine. A Punnett square is used to show the possible genes inherited from two parents.
The genotype is the actual genetic makeup relating to a trait. An allele that dominates or masks the presence of another allele is a dominant allele (represented by an upper case letter) The allele whose presence is completely masked is the recessive allele (represented by a lower case letter). Phenotype is the physical expression of the genotype.
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