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Scientific study of heredity and hereditary variations


Transmission of characteristics from parents to offspring


Fusion of sperm and egg that are provided by the same individual


Fusion of sperm and egg provided by two different individuals


Organism for which sexual reproduction produces offspring with inherited traits identical to those of the parents; organisms are homozygous for the characteristic under consideration


Offspring of two parents that differ in one or more inherited traits; an individual that is heterozygous for one or more pairs of genes

Genetic cross

Cross-fertilization of two different varieties of an organism or two different species; hybridization

P generation

Parent individuals from which offspring are derived in inheritance studies; P = parental

F1 generation

Offspring of two P generation individual; F = filial

F2 generation

Offspring of two F1 generation individuals

Monohybrid cross

An experimental mating of individuals differing at one genetic locus


Alternative form of a gene


Having two identical alleles for a given gene


Having tow different alleles for a given gene

Dominant allele

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

Recessive allele

In a heterozygote, allele that has no noticeable effect on the phenotype

Law of segregation

Individuals have two alleles for each gene and that when gametes form by meiosis, the two alleles separate and each resulting gamete possesses only one allele of each gene

Punnett square

Diagram used in the study of inheritance to show the results of random fertilization


The expressed traits of an organism; outward appearance


Genetic makeup of an organism


Particular site where a gene is found on a chromosome; homologous chromosomes have corresponding gene loci

Dihybrid cross

Experimental mating of individuals differing at two loci

Law if independent assortment

General rule of inheritance that when gametes form during meiosis, each pair of alleles for a particular characteristic segregate independently

Rule of multiplication

The probability of a compound event is the product of the separate probabilities of the independent events

Wild-type traits

Traits most commonly found in nature


Family tree representing the occurrence of heritable traits in parents and offspring across a number of generations


Individual who is heterozygous for a recessive inherited disorder and who does not show symptoms of that disorder


Mating of close relatives


Form of human dwarfism caused by a single dominant allele; homozygous condition is lethal

Huntington's disease

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

Incomplete dominance

Type of inheritance in which the phenotype of a heterozygote is intermediate between the two types of homozygous phenotypes


Inherited human disease characterized by an excessively high level of cholesterol in the blood

ABO blood groups

Genetically determined human blood classes that are based on the presence or absence of carbohydrates A and B in the surface of red blood cells


Expression of two different alleles of a genotype in a heterozygote


Control of more than one phenotypic characteristic by a single gene

Sickle-cell disease

Genetic disorder in which red blood cells have abnormal hemoglobin molecules and take on an abnormal shape

Polygenic inheritance

The additive effect of two or more gene loci on a single phenotypic characteristic

Chromosome theory of inheritance

Basic biological principle stating that genes are located on chromosomes and that the behavior of chromosomes during meiosis accounts for inheritance patterns

Linked genes

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

Recombination frequency

With respect to two given genes, the number of recombinant progeny from a mating divided by the total number of progeny; recombinant progeny carry different combinations of alleles than their parents as a result of independent assortment and crossing over

Linkage map

Map of a chromosome showing the relative position of genes

Sex-linked gene

Gene located on a sex chromosome

Red-green color blindness

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


Sex-linked human genetic blood disorder caused by a recessive allele that affects proper blood clotting

Duchenne muscular dystrophy

Human genetic disease caused by sex-linked recessive allele and characterized by progressive weakening and a loss of muscle tissue

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