First: alternative versions of genes (alleles) account for variations in inherited characters.Second: for each character, an organism inherits two alleles, one from each parent.Third: if the two alleles at a locus differ, then one (the dominant allele) determines the organism’s appearance, and the other (the recessive allele) has no noticeable effect on appearance.Fourth (the law of segregation): the two alleles for a heritable character separate (segregate) during gamete formation and end up in different gametes.