Genetics and Punnett Squares

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Heredity Noun

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[huh-red-i-tee]

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Heredity

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The passing of traits or characteristics from parents to their offspring through the transmission of genetic information.

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Example: This pedigree chart shows how a genetic trait is passed from parents to offspring through generations, which is the definition of heredity.

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Gene Noun

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[jeen]

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Gene

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A specific segment of DNA that codes for a protein or RNA, thereby controlling an inherited characteristic or trait.

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Example: This diagram shows that a gene is a specific section of a DNA molecule, which is tightly coiled into a chromosome found 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 variant form of a specific gene, where an individual inherits two copies for a trait, one from each parent.

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Example: This image shows that an allele is a specific version of a gene (like 'A' or 'a') located on a chromosome, and different combinations create genotypes.

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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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An allele that is phenotypically expressed as long as at least one copy is present in the organism's genotype.

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Example: This diagram shows different allele combinations on chromosomes. The heterozygous 'Aa' combination is the key condition where a dominant allele would express its trait.

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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 that is phenotypically expressed only when two copies are present and no dominant allele is present.

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Example: A recessive allele, shown as a lowercase 'a', is a version of a gene that is only expressed when paired with another recessive allele (aa).

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Genotype Noun

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[jee-noh-tahyp]

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Genotype

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The specific genetic makeup of an organism, representing the combination of alleles inherited from its parents for a trait.

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Example: This image shows how a genotype is the combination of alleles (letters like B or b) on a pair of chromosomes, such as BB, bb, or Bb.

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Phenotype Noun

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[fee-noh-tahyp]

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Phenotype

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The observable physical appearance or biochemical characteristic of an organism as a result of its expressed genotype.

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Example: This diagram shows how different genotypes (the genetic code, like AA, Aa, or aa) result in a specific phenotype (the observable physical trait, like brown or blue eyes).

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Homozygote Noun

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[hoh-moh-zahy-goht]

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Homozygote

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An organism that inherits two identical alleles for a particular gene from its parents, also known as purebred.

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Example: This diagram shows a homozygous organism has a pair of identical alleles for a gene, like two dominant 'A's or two recessive 'a's.

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Homozygous Dominant Noun

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

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Homozygous Dominant

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A genotype consisting of two dominant alleles for a particular trait, which are represented by two capital letters.

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Example: This diagram shows a pair of homologous chromosomes with two identical dominant alleles (AA), represented by the two black bands, which defines a homozygous dominant trait.

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Homozygous Recessive Noun

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

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Homozygous Recessive

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A genotype consisting of two recessive alleles for a particular trait, which are represented by two lowercase letters.

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Example: This Punnett square shows a genetic cross where two of the four possible offspring have the genotype 'aa', which is defined as homozygous recessive.