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Biology LibreTexts


  • Symbols are used to denote the alleles, or genotype, of a locus. 
  • Phenotype depends on the alleles that are present, their dominance relationships, and sometimes also interactions with the environment and other factors. 
  • In a diploid organism, the alleles can be homozygous, heterozygous or hemizygous.  
  • Allelic interactions at a locus can be described as dominant vs. recessive, incomplete dominance, or co-dominance.
  • Two different genes can be on the same chromosome (linked) or on different ones (unlinked)
  • Steps:
    • Can you identify the mutant?  Name the gene after its phenotype
    • If you cannot tell which allele is mutant, name the gene after the recessive allele
    • Capitalize the first letter for the dominant allele; use lower-case for the recessive allele
    • If genes are linked, write the gene symbols together on each side of the slash.  If genes are unlinked, they appear on different sides of a semicolon