DNA key terms

• Allele


  Different versions of the same gene
• Dominant


  One of the alleles that gets expressed
• Recessive


  One of the alleles that does not get expressed when the dominant allele is present
• Homozygous


  Having two of the same alleles for a gene
• Heterozygous


  Having two different alleles for a gene
• Heterozygous mouse with one purple and one green allele


  The dominant allele (purple) gets expressed
• The only way to have a green mouse is if both of its alleles were for green fur, which would be called homozygous recessive
• The purple allele will always be expressed when it's present, regardless of whether the mouse is heterozygous or homozygous for the purple allele
• Genotype


  The entire collection of alleles that an organism has
• Phenotype


  The characteristics that an organism gets from its genotype
• The heterozygous mouse, homozygous dominant mouse, and homozygous recessive mouse all have different genotypes but the heterozygous mouse and homozygous dominant mouse have the same phenotype (purple fur)