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Science · Grades 9–12

Genetics and inheritance

20 key concepts, retrieval questions and a learning checkpoint.

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Dominant does not mean more common, stronger or better. A simple genetic model may not describe a complex human trait.

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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.

Test your recall

  1. Genetics and inheritance: which term fits this description? One of the alternative versions of a gene at a particular locus.

    1. Zygote
    2. Gamete
    3. Homozygous
    4. Allele

  2. Genetics and inheritance: which term fits this description? The allele combination an organism has at one or more loci.

    1. Genotype
    2. Heterozygous
    3. Incomplete dominance
    4. Codominance

  3. Genetics and inheritance: which term fits this description? An observable characteristic produced through genes and environment.

    1. Recessive allele
    2. Codominance
    3. Allele
    4. Phenotype

Check and explain

Answers and marking notes
  1. Allele

    Allele: One of the alternative versions of a gene at a particular locus.

  2. Genotype

    Genotype: The allele combination an organism has at one or more loci.

  3. Phenotype

    Phenotype: An observable characteristic produced through genes and environment.

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.