Definitions

• .Gene = a sequence of bases on a DNA molecule that codes for a sequence of amino acids in a polypeptide chain e.g. eye colour
• Locus = the position of a gene on a chromosome
• Homologous chromosomes = One paternal and one maternal chromosome
• .Alleles = different versions of a gene e.g. blue eyes
• .Dominant allele = effect is seen even with only one copy of the allele
• .Recessive allele = effect is shown if two copies are present
• .Heterozygous = Two different alleles for a gene e.g. Tt
• .Homozygous = two identical alleles for a gene e.g. TT or tt
• Carrier = A person with a heterozygous genotype for a genetic disease
• .Genotype = the alleles in an organism
• .Phenotype = the characteristics of an organism as a result of its genes and the environment.
• .Incomplete dominance = one allele for a specific trait is not completely expressed over its paired allele. Results in a third phenotype, which expressed physical trait is a combination of the dominant and recessive phenotypes. (grey cow)