7.1.1 Key Terms in Genetics

• Gene = a length of DNA that codes for a single polypeptide/protein
• Genome = the complete set of genes (DNA) found within an organism's cells.
• Alleles = different versions of a gene at a particular locus on a chromosome.
• Locus = the position of a gene on a chromosome (pl = loci)
• Genotype = genetic constitution of an organism
• Phenotype = expression of the genotype and its interaction with the environment
• There may be many alleles of a single gene
• Codominant Alleles → both alleles are equally dominant & equally expressed in the phenotype (eg AB)
• Heterozygous → two different alleles, one from each parent, e.g. Ff
• Homozygous → 2 identical alleles, recessive allele is expressed
• Dominant → the allele that is always expressed in the phenotype
• Recessive → when the phenotype is expressed only if no dominant allele is present
• Autosomes → any chromosome that is not a sex chromosome
• Autosomal Linkage

  • Two or more genes located on the same autosome/chromosome
  • Less likely to be separated during crossing over so are inherited together 
  • Changes phenotypic ratio
• Sex Linkage 

  • Gene is on the X chromosome
  • Males are more likely to have recessive condition because they only require one copy of the sex linked recessive allele for expression