Molecular Biology Chapter 14 Vocabulary

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Character

Back 1

An observable heritable feature that may vary among individuals.

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Trait

Back 2

One of two or more detectable variants in a genetic character.

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True-breeding

Back 3

Referring to organisms that produce offspring of the same variety over many generations of self-pollination.

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Hybridization

Back 4

In genetics, the mating, or crossing, of two true-breeding varieties.

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P Generation

Back 5

The true-breeding (homozygous) parent individuals from which F1 hybrid offspring are derived in studies of inheritance; P stands for “parental”.

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F1 Generation

Back 6

The first filial, hybrid (heterozygous) offspring arising from a parental (P generation) cross.

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F2 Generation

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The offspring resulting from interbreeding (or self-pollination) of the hybrid F1 generation.

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Alleles

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Any of the alternative versions of a gene that may produce distinguishable phenotypic effects.

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Dominant Allele

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An allele that is fully expressed in the phenotype of a heterozygote.

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Recessive Allele

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An allele whose phenotypic effect is not observed in a heterozygote.

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Law of Segregation

Back 11

Mendel’s first law, stating that two alleles in a pair segregate (separate from each other) into different gametes during gamete formation.

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Punnett Square

Back 12

A diagram used in the study of inheritance to show the predicted genotypic results of random fertilization in genetic crosses between individuals of known genotype.

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Homozygous

Back 13

Having two identical alleles for a given gene.

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Heterozygous

Back 14

Having two different alleles for a given gene.

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Phenotype

Back 15

The observable physical and physiological traits of an organism, which are determined by its genetic makeup.

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Genotype

Back 16

The genetic makeup, or set of alleles, of an organism.

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Testcross

Back 17

Breeding an organism of unknown genotype with a homozygous recessive individual to determine the unknown genotype. The ratio of phenotypes in the offspring reveals the unknown geneotype.

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Monohybrids

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An organism that is heterozygous with respect to a single gene of interest. All the offspring from a cross between parents homozygous for different alleles are monohybrids. For example, parents of genotypes AA and aa produce a monohybrid of genotype Aa.

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Monohybrid Cross

Back 19

A cross between two organisms that are heterozygous for the character being followed (or the self-pollination of a heterozygous plant).

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Dihybrid

Back 20

An organism that is heterozygous with respect to two genes of interest. All the offspring from a cross between parents doubly homozygous for different alleles are dihybrids. For example, parents of genotypes AABB and aabb produce a dihybrid of genotype AaBb.

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Dihybrid Cross

Back 21

Referring to a fungal mycelium with two haploid nuclei per cell, one from each parent.

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Law of Independent Assortment

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Mendel’s second law, stating that each pair of alleles segregates, or assorts, independently of each other pair during gamete formation; applies when genes for two characters are located on different pairs of homologous chromosomes or when they are far enough apart on the same chromosome to behave as though they are on different chromosomes.

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Multiplication Rule

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A rule of probability stating that the probability of two or more independent events occurring together can be determined by multiplying their individual probabilities.

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Addition Rule

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A rule of probability stating that the probability of any one of two or more mutually exclusive events occurring can be determined by adding their individual probabilities.

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Complete Dominance

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The situation in which the phenotypes of the heterozygote and dominant homozygote are indistinguishable.

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Incomplete Dominance

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The situation in which the phenotype of heterozygotes is intermediate between the phenotypes of individuals homozygous for either allele.

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Codominance

Back 27

The situation in which the phenotypes of both alleles are exhibited in the heterozygote because both alleles affect the phenotype in separate, distinguishable ways.

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Tay-Sachs Disease

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A human genetic disease caused by a recessive allele for a dysfunctional enzyme, leading to accumulation of certain lipids in the brain. Seizures, blindness, and degeneration of motor and mental performance usually become manifest a few months after birth, followed by death within a few years.

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Pleiotropy

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The ability of a single gene to have multiple effects.

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Epistasis

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A type of gene interaction in which the phenotypic expression of one gene alters that of another independently inherited gene.

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Quantitative Characters

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A heritable feature that varies continuously over a range rather than in an either-or fashion.

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Polygenic Inheritance

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An additive effect of two or more genes on a single phenotypic character.

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Norm of Reaction

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The range of phenotypes produced by a single genotype, due to environmental influences.

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Multifactorial

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Referring to a phenotypic character that is influenced by multiple genes and environmental factors.

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Pedigree

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A diagram of a family tree with conventional symbols, showing the occurrence of heritable characters in parents and offspring over multiple generations.

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Carrier

Back 36

In genetics, an individual who is heterozygous at a given genetic locus for a recessively inherited disorder. The heterozygote is generally phenotypically normal for the disorder but can pass on the recessive allele to offspring.

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Cystic Fibrosis

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A human genetic disorder caused by a recessive allele for a chloride channel protein; characterized by an excessive secretion of mucus and consequent vulnerability to infection; fatal if untreated.

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Sickle Cell Disease

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A recessively inherited human blood disorder in which a single nucleotide change in the β-globin gene causes hemoglobin to aggregate, changing red blood cell shape and causing multiple symptoms in afflicted individuals.

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Duchenne muscular dystrophy

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A human genetic disease caused by a sex-linked recessive allele; characterized by progressive weakening and a loss of muscle tissue.

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Huntington’s Disease

Back 40

A human genetic disease caused by a dominant allele; characterized by uncontrollable body movements and degeneration of the nervous system; usually fatal 10 to 20 years after the onset of symptoms.

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Amniocentesis

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A technique associated with prenatal diagnosis in which amniotic fluid is obtained by aspiration from a needle inserted into the uterus. The fluid and the fetal cells it contains are analyzed to detect certain genetic and congenital defects in the fetus.

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Chronic Villus Sampling (CVS)

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A technique associated with prenatal diagnosis in which a small sample of the fetal portion of the placenta is removed for analysis to detect certain genetic and congenital defects in the fetus.