Traits and Reproduction

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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 molecule, thereby controlling an organism's expressed characteristics.

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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 specific variant form of a gene, with individuals inheriting one allele from each parent for every gene.

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Example: This diagram shows alleles as different forms of a gene (A or a) located on a pair of chromosomes, illustrating homozygous (AA, aa) and heterozygous (Aa) 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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An allele that is phenotypically expressed even when only one copy is present in an organism's genotype.

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Example: This diagram shows that a dominant allele, represented by a capital letter 'A', can be present in a homozygous (AA) or heterozygous (Aa) pair.

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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 only expressed in the phenotype when two copies are present in the genotype.

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Example: This Punnett square shows that the allele for white flowers ('b') is recessive because the white flower only appears when two 'b' alleles are combined.

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Genotype Noun

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[jee-noh-tiep]

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Genotype

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The specific genetic makeup of an organism, representing the combination of alleles inherited for a particular gene.

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Example: This diagram shows a genotype is the combination of alleles (like B and b) on chromosomes, which can be homozygous (BB or bb) or heterozygous (Bb).

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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 appearance or expressed traits of an organism, which result from its specific genetic makeup.

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Example: This image shows different bird beak shapes adapted for various foods. These observable physical differences, like a crushing or probing beak, are examples of phenotypes.

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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 specific gene from its parents.

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Example: This diagram shows that a homozygote has two identical alleles (e.g., AA or aa) for a gene on a pair of chromosomes.

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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.

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Example: This Punnett square shows how two heterozygous parents (Bb) can pass on different alleles, resulting in offspring that can be homozygous (BB, bb) or heterozygous (Bb).

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Punnett Square Noun

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[puhn-it skwair]

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Punnett Square

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A diagram used to predict the probability of an offspring having a particular genotype based on parental genotypes.

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Example: This diagram shows a Punnett square predicting offspring traits by combining one parent's alleles (Gg) with another's (gg) to determine possible genetic outcomes.

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Monohybrid Cross Noun

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[mon-oh-hy-brid kros]

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Monohybrid Cross

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A genetic cross between two organisms that tracks the inheritance of a single characteristic or trait.

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Example: This Punnett square shows how alleles from two parents (Pp) combine, predicting the possible genotypes (PP, Pp, pp) of their offspring for a single trait.