Science · Grades 9–12
Genetics and inheritance · quick reference
Dominant does not mean more common, stronger or better. A simple genetic model may not describe a complex human trait.
Key terms at a glance
Allele
One of the alternative versions of a gene at a particular locus.
Genotype
The allele combination an organism has at one or more loci.
Phenotype
An observable characteristic produced through genes and environment.
Homozygous
Having two identical alleles at a particular locus in a diploid organism.
Heterozygous
Having two different alleles at a particular locus in a diploid organism.
Dominant allele
An allele expressed in a heterozygote under a simple complete-dominance model.
Recessive allele
An allele whose effect is masked in a heterozygote under complete dominance.
Gamete
A reproductive cell carrying one set of chromosomes in a typical sexual life cycle.
Zygote
The cell formed when two gametes fuse.
Meiosis
Cell division that reduces chromosome-set number for a sexual life cycle.
Mitosis
Nuclear division that usually produces genetically equivalent daughter nuclei.
Mutation
A change in a DNA sequence.
Codon
A three-nucleotide RNA sequence specifying an amino acid or translation signal.
Transcription
Synthesis of an RNA molecule using a DNA template.
Translation
Assembly of a polypeptide using the sequence of an mRNA molecule.
Punnett square
A table used to organize possible allele combinations in a genetic cross.
Incomplete dominance
Inheritance in which a heterozygote has an intermediate phenotype.
Codominance
Inheritance in which both alleles contribute distinctly to the heterozygote phenotype.
Sex-linked gene
A gene located on a sex chromosome.
Polygenic trait
A characteristic influenced by more than one gene.
Further reading and review references
These are reference links, not copied exercises, institutional endorsement or proof of independent review.
Learning preview · teacher review required. Grade bands are approximate, not official curriculum alignment.