Dominant and Recessive Traits

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Gene Noun

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[jeen]

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Gene

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A segment of DNA that codes for a protein or RNA, controlling the expression of one or more characteristics.

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Example: This diagram shows that a gene is a specific section of a DNA molecule, which is tightly coiled to form a chromosome inside a cell's nucleus.

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Allele Noun

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[uh-leel]

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Allele

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A specific variant form of a gene that is inherited from a parent, determining a particular trait.

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Example: This diagram shows alleles, which are different versions of a gene (like 'A' and 'a'), located on paired chromosomes, forming different genetic combinations.

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Dominant Allele Noun

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[dom-uh-nuhnt uh-leel]

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Dominant Allele

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The allele that is fully expressed in the phenotype, masking the effect of a different, recessive allele when present.

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Example: This Punnett square shows that when the 'P' allele is present (genotypes PP or Pp), the flower is purple, making 'P' the dominant allele.

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Recessive Allele Noun

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[ri-ses-iv uh-leel]

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Recessive Allele

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An allele whose phenotypic effect is masked by a dominant allele and is only expressed in a homozygous state.

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Example: This diagram shows a recessive allele ('a') is a gene version that is only expressed as a trait when two copies are present (homozygous).

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Genotype Noun

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[jee-noh-tiep]

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Genotype

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The specific combination of alleles that an organism possesses for a particular genetic trait or set of traits.

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Example: This diagram shows the three possible genotypes for a single gene: homozygous dominant (AA), heterozygous (Aa), and homozygous recessive (aa).

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Phenotype Noun

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[fee-noh-tiep]

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Phenotype

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The observable physical or biochemical characteristics of an organism, as determined by its genotype and environmental influences.

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Example: This diagram shows how an organism's genetic makeup (genotype) determines its observable physical traits (phenotype), such as eye color, through dominant and recessive alleles.

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Homozygote Noun

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[hoh-moh-zy-goht]

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Homozygote

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An organism that has inherited two identical alleles for a particular gene from its parents for a specific trait.

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Example: This diagram shows that a homozygote has two identical alleles for a gene, represented by two matching letters like 'BB' or 'bb' on a chromosome pair.

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Homozygous dominant Noun

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[hoh-moh-zy-guhs dom-uh-nuhnt]

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Homozygous dominant

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A genotype characterized by the presence of two identical dominant alleles for a specific gene, expressing the dominant trait.

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Example: This diagram shows that homozygous dominant means having two identical dominant alleles (AA) for a trait, one on each chromosome in a pair.

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Homozygous recessive Noun

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[hoh-moh-zy-guhs ri-ses-iv]

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Homozygous recessive

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A genotype characterized by the presence of two identical recessive alleles for a specific gene, expressing the recessive trait.

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Example: This Punnett square shows that when an organism inherits two identical recessive alleles (b and b), it has a homozygous recessive genotype (bb) and displays the recessive trait (a white flower).

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Heterozygote Noun

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[het-er-oh-zy-goht]

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Heterozygote

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An organism that has inherited two different alleles for a particular gene from its parents for a specific trait.

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Example: A heterozygote has two different alleles (B and b) for a specific gene, one on each chromosome of a homologous pair.