According to Mendelian inheritance, variations in an organism's phenotype (observable physical and behavioral characteristics) are due in part to variations in its genotype (particular set of genes). Each gene specifies a particular trait with different sequence of a gene (alleles) giving rise to different phenotypes. Most eukaryotic organisms (such as the pea plants Mendel worked on) have two alleles for each trait, one inherited from each parent.:20
According to Mendelian inheritance, what is part of the cause of variations in an organism's phenotype? What sort of characteristics are described by an organism's phenotype? What is a genotype? What specifies a particular trait with a different sequence of alleles? How many alleles do most eukaryotic organisms have for each trait?