Dominant vs recessive
Quick answer: Dominant alleles shape heterozygote phenotype; recessive alleles usually show only when homozygous.
Dominance is a relationship between alleles for a phenotype, not a moral or frequency ranking.
Use the table rows first for rapid contrast, then read the similarity and difference sections to lock in exam-ready language. Finish with the “when to use which term” guidance before attempting the self-checks.
Side-by-side comparison
| Feature | Dominant allele | Recessive allele |
|---|---|---|
| Heterozygote | Phenotype shows dominant trait | Recessive trait masked |
| Homozygote needed? | Not required to see dominant phenotype | Typically yes for recessive phenotype |
| Carrier idea | Not called a carrier for dominant trait usually | Heterozygotes can carry recessive alleles |
| Frequency | Independent of dominance | Independent of recessiveness |
| Molecular basis | Various mechanisms possible | Various mechanisms possible |
| Notation | Often capital letter | Often lowercase letter |
Similarities
Both are alleles of the same gene in Mendelian models.
Both are inherited via segregation.
Differences
Expression pattern in heterozygotes differs.
Phenotypic ratios in crosses differ.
When each term applies
Use these terms for simple Mendelian traits first.
Switch to incomplete/codominance language when needed.
Common confusion
Dominant ≠ better; recessive ≠ rare always.
Common questions
In Aa with A dominant, which trait shows?
Dominant.
When does aa show?
Homozygous recessive phenotype.
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Related topics: Dominant allele · Recessive allele · Browse the learning library · All comparisons · Study guides