Essential Biology Chapter 9 Vocabulary

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Heredity

Back 1

The transmission of traits from one generation to the next.

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Genetics

Back 2

The scientific study of heredity (inheritance).

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Character

Back 3

A heritable feature that varies among individuals within a population, such as flower color in pea plants.

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Trait

Back 4

A variant of a character found within a population, such as purple flowers in pea plants.

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Hybrids

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The offspring of parents of two different species or of two different varieties of one species; the offspring of two parents that differ in one or more inherited traits; an individual that is heterozygous for one or more pairs of genes.

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Cross

Back 6

The cross-fertilization of two different varieties of an organism or of two different species; also called hybridization.

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P generation

Back 7

The parent individuals from which offspring are derived in studies of inheritance. P stands for parental.

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F1 generation

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The offspring of two parental (P generation) individuals. F1 stands for first filial.

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F2 generation

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The offspring of the F1 generation. F2 stands for second filial.

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Monohybrid cross

Back 10

A mating of individuals differing at one genetic locus.

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Alleles

Back 11

An alternative version of a gene.

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Homozygous

Back 12

Having two identical alleles for a given gene.

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Heterozygous

Back 13

Having two different alleles for a given gene.

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Dominant allele

Back 14

In a heterozygote, the allele that determines the phenotype with respect to a particular gene.

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Recessive allele

Back 15

In heterozygotes, the allele that has no noticeable effect on the phenotype.

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Law of segregation

Back 16

A general rule of inheritance, first proposed by Gregor Mendel, that states the two alleles in a pair segregate (separate) into different gametes during meiosis.

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Punnett square

Back 17

A diagram used in the study of inheritance to show the results of random fertilization.

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Phenotype

Back 18

The expressed traits of an organism.

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Genotype

Back 19

The genetic makeup of an organism.

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Locus

Back 20

The particular site where a gene is found on a chromosome. Homologous chromosomes have corresponding gene loci.

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Dihybrid cross

Back 21

A mating of individuals differing at two genetic loci.

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Law of independent assortment

Back 22

A general rule of inheritance, first proposed by Gregor Mendel, that states that when gametes form during meiosis, each pair of alleles for a particular character segregate (separate) independently of each other pair.

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Testcross

Back 23

The mating between an individual of unknown genotype for a particular character and an individual that is homozygous recessive for that same character.

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Rule of multiplication

Back 24

A rule stating that the probability of a compound event is the product of the separate probabilities of the independent events.

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Wild-type traits

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The trait most commonly found in nature.

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Pedigree

Back 26

A family tree representing the occurrence of heritable traits in parents and offspring across a number of generations.

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Carriers

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An individual who is heterozygous for a recessively inherited disorder and who therefore does not show symptoms of that disorder.

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Cystic fibrosis (CF)

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A genetic disease that occurs in people with two copies of a certain recessive allele; characterized by an excessive secretion of mucus and consequent vulnerability to infection; fatal if untreated.

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Inbreeding

Back 29

The mating of close relatives.

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Achondroplasia

Back 30

A form of human dwarfism caused by a single dominant allele. The homozygous condition is lethal.

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Huntington's disease

Back 31

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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Incomplete dominance

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A type of inheritance in which the phenotype of a heterozygote (Aa) is intermediate between the phenotypes of the two types of homozygotes (AA and aa).

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Hypercholesterolemia

Back 33

An inherited human disease characterized by an excessively high level of cholesterol in the blood.

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ABO blood groups

Back 34

Genetically determined classes of human blood that are based on the presence or absence of carbohydrates A and B on the surface of red blood cells. The ABO blood group phenotypes, also called blood types, are A, B, AB, and O.

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Codominant

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Expressing two different alleles of a gene in a heterozygote.

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Pleiotropy

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The control of more than one phenotypic character by a single gene.

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Sickle-cell disease

Back 37

A genetic disorder in which the red blood cells have abnormal hemoglobin molecules and take on an abnormal shape.

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Polygenic inheritance

Back 38

The additive effect of two or more genes on a single phenotypic characteristic.

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Chromosome theory of inheritance

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A basic principle in biology stating that genes are located on chromosomes and that the behavior of chromosomes during meiosis accounts for inheritance patterns.

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Linked genes

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Genes located close enough together on a chromosome that they are usually inherited together.

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Recombination frequency

Back 41

With respect to two given genes, the number of recombinant progeny from a mating divided by the total number of progeny. Recombinant progeny carry combinations of alleles different from that seen in either of the parents as a result of independent assortment of chromosomes and crossing over.

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Linkage map

Back 42

A map of a chromosome showing the relative positions of genes.

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Sex-linked gene

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A gene located on a sex chromosome.

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Red-green colorblindness

Back 44

A common sex-linked human disorder involving several genes on the X chromosome and characterized by a malfunction of light-sensitive cells in the eyes; affects mostly males but also homozygous females.

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Hemophilia

Back 45

A human genetic disease caused by a sex-linked recessive allele and characterized by excessive bleeding following injury.