dna two - key terms

• Allele


  Different versions of the same gene
• Homozygous


  Having two of the same alleles for a particular gene
• Heterozygous


  Having two different alleles for a particular gene
• Dominant allele


  The allele that gets expressed when present, regardless of whether the organism is homozygous or heterozygous for that allele
• Recessive allele


  The allele that only gets expressed when the organism is homozygous for that allele
• Genotype


  The entire collection of alleles that an organism has
• Phenotype


  The characteristics that an organism displays, which are determined by its genotype
• Characteristics are often determined by the interaction of multiple genes, not just a single gene
• Genes code for different forms of the same protein, which are called alleles
• If an organism is heterozygous for a trait, the dominant allele will be expressed
• The only way to have a recessive trait expressed is if the organism is homozygous for the recessive allele
• Our body cells contain two copies of each chromosome, one from our mother, and one from our father. This means that we also have two versions of each gene (each different version is a different allele).
• In order to be expressed, how many recessive alleles must be present? 

  Two
• Genotype (course definition)


  The two alleles present for a particular gene