Pedigrees

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Pedigree Noun

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[ped-i-gree]

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Pedigree

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A chart showing family relationships and tracking how a specific trait is inherited through several generations.

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Example: This chart, called a pedigree, uses symbols to show how a trait is passed down through generations of a family.

Front

Genotype Noun

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[jee-noh-tahyp]

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Genotype

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The specific genetic makeup or combination of alleles an organism possesses for a particular trait.

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Example: This diagram shows genotype as the combination of alleles on chromosomes. An individual can be homozygous (AA or aa) or heterozygous (Aa) for a gene.

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Allele Noun

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[uh-leel]

Back

Allele

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One of two or more alternative forms of a gene that are found at the same place on a chromosome.

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Example: This diagram shows that alleles are different versions of a gene (like 'A' or 'a') found at the same spot on a pair of chromosomes.

Front

Dominant Allele Noun

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[dom-uh-nuhnt uh-leel]

Back

Dominant Allele

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An allele that expresses its trait even when paired with a different allele, masking the recessive allele's effect.

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Example: This diagram shows that when a dominant allele (A) is present with a recessive allele (a), the dominant trait is expressed and masks the recessive one.

Front

Recessive Allele Noun

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[ri-ses-iv uh-leel]

Back

Recessive Allele

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An allele whose effect is masked by a dominant allele and is only expressed when two copies are present.

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Example: A recessive allele (like 'b') is a version of a gene that is only expressed as a trait when two copies are present, as in the homozygous 'bb' pair.

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Homozygous Adjective

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[hoh-moh-zahy-guhs]

Back

Homozygous

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Describes an individual having two identical alleles for a particular gene, such as two dominant or two recessive alleles.

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Example: This diagram shows that a homozygous genotype has two identical alleles (like AA or aa) for a gene on a pair of chromosomes.

Front

Heterozygous Adjective

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[het-er-oh-zahy-guhs]

Back

Heterozygous

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Describes an individual having two different alleles for a particular gene, such as one dominant and one recessive allele.

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Example: This diagram shows a pair of homologous chromosomes with two different alleles (B and b) for the same gene, which defines a heterozygous genotype.

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Carrier Noun

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[kar-ee-er]

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Carrier

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An individual who has a recessive allele for a trait but does not express it due to a dominant allele.

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Example: This diagram shows two carrier parents, who each have one normal and one mutated gene, and the possible genetic outcomes for their children.

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Autosomes Noun

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[aw-tuh-sohmz]

Back

Autosomes

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Any chromosome that is not a sex chromosome, comprising the first 22 homologous pairs of chromosomes in humans.

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Example: This diagram shows all 23 pairs of human chromosomes, separating the 22 pairs of autosomes from the one pair of sex chromosomes.

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Sex Chromosomes Noun

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[seks kroh-muh-sohmz]

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Sex Chromosomes

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The pair of chromosomes that determines an individual's biological sex, designated as the 23rd pair in humans.

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Example: This image shows that humans have two types of sex chromosomes: XY, which typically results in a male, and XX, which typically results in a female.