used to describe a gene that produces an effect in an organism only when its matching allele is identical

that allele which will not be expressed phenotypically unless present as both copies of the genetic information for the trait.

In genetics it is known that at a particular point on the genome of an organism (a locus), there may be two or more different versions of the gene (alleles). Generally, one of these alleles will be expressed in preference to another; the one that is expressed is called dominant, the other is called recessive. A recessive allele is usually not expressed at all unless both loci have the recessive allele - a 'double recessive' or 'homozygous recessive'. One example of this is albinism, where the body produces no pigment at all; this is only caused when a specific locus within the genome has a recessive gene on both chromosomes at the same locus.

A gene that is phenotypically manifest in the homozygous state but is masked in the presence of a dominant allele.

relating to alleles which are not reflected in the phenotype when present as one member of a heterozygous pair. They determine the phenotype only when they are present in the homozygous state.

A genetically determined characteristic that is expressed only in the homozygous recessive condition.

Refers to an allele that cannot control the phenotype unless it is the only kind of allele present, as in a homozygote or hemizygote. Also refers to the trait or phenotype produced when only a recessive allele is present. The opposite of recessive is dominant.

the allele overshadowed by the dominant allele.

An allele which has little or no effect on the phenotype of an organism when paired with a more dominant allele; it only has an effect when paired with another recessive allele.

Refers to genetic disorders in which a person must have two copies of the mutated gene to develop the disorder.

Refers to a characteristic that is apparent only when both copies of the gene encoding it are present—one from the mother and one from the father.

a gene that hides a certain dominant trait

The allele that is not expressed in a heterozygote.

The phenotype of a recessive allele can be masked by the presence of a dominant allele. The phenotype is only apparent when both alleles are recessive. For example, light colored eyes are recessive to dark colored eyes, so an individual with an allele for blue eyes will only have that phenotype, if he or she has two copies of that allele, i.e. no allele for dark colored eyes. (opposite of 'dominant')

Refers to the member of a pair of alleles that fails to be expressed in the phenotype of the organism when the dominant member is present. Also refers to the phenotype of an individual that has only the recessive allele.

A gene that shows up phenotypically in its homozygous state but is masked in the presence of a dominant allele. Both copies of the gene must be the recessive form in order for a recessive phenotype or characteristic to be observed.

The gene that exerts its effect when presents in both homologous chromosomes. If present in one chromosome is masked by the dominant effect of the gene present in the other chromosome. As shown below many diseases are associted with recessive genes.

A gene that only produces its affect when both copies present are identical.  A recessive gene trait will be passed on to children with only a 1 in 4 chance.

One of alleles which does not express himself in the phenotype, because the expression is masked by the dominant allele.

An allele that is not expressed in the heterozygous condition. Also the phenotype of the homozygote of a recessive allele.

a trait that is not physically expressed in heterozygotes. In order for the trait to be expressed, there must be two copies of the allele.

Allele which will not express unless it is homozygous.

requires a copy of the gene from both parents to exhibit the trait. Having only one copy of the gene makes the dog a carrier of the trait, and he will never exhibit the trait – unless the gene is located on the ‘X’ or sex chromosome. sarcoma – tumor formed of connective tissue cells: bone cartilage, muscle, blood vessel, or lymphoid tissue.

A disease or trait that is expressed only when the mutation occurs in both genes of a gene pair. Males and females are equally likely to be affected in the case of autosomal recessive diseases, which result from a gene (allele) residing on an autosomal chromosome. The disorder can appear suddenly with no prior history of it in a family. Examples: cystic fibrosis, sickle cell anemia, color blindness in males.

the weaker gene of a pair of genes.

of genes; producing its characteristic phenotype only when its allele is identical

The member of an allelic pair that is not expressed when the other, dominant allele is present on the homologous chromosome.

gene whose phenotypic expression is masked by its dominant allele.

Describes a trait or disorder requiring the presence of two copies of a gene mutation at a particular locus in order to express observable phenotype; specifically refers to genes on one of the 22 pairs of autosomes (non-sex chromosomes) Related Terms: allele frequency ; carrier ; carrier testing ; compound heterozygote ; consanguinity ; heterozygote ; homozygote ; mode of inheritance

an allele whose effects are shown only when the dominant allele is absent

(genetics) if the required allele (a type of gene) is not present in both members of a pair of chromosomes then that allele is not expressed. A mutation is said to be recessive if an individual must inherit two copies of the mutant gene, one from each parent, to show the mutant trait. Individuals with one mutant and one normal gene appear normal. They are called ÒcarriersÓ.

An allele or gene that is not expressed or "shown" in the phenotype because it is "hidden" by the dominant gene.

The property of an allele whereby possessing either one or zero copies of the allele results in the same phenotype. Having two copies allows the allele's function to be seen. Contrast with dominant

Any genetic trait which requires you to have two of the same gene to show that trait outwardly

an allele, or the corresponding trait, that is manifest only in the homozygote, contrast with dominant.

A genetic condition that appears only in as WHO property received two copies or a mutant gene, one from each parent.

re-SESS-ive An allele whose expression is masked by the activity of another allele. 265

a condition which is expressed only in individuals with two copies of a mutant gene

Two identical alleles at a locus producing a particular characteristic, trait, or disease.

An inherited effect observed when both copies of a gene (both alleles) are mutated.

An allele whose effect is masked by the presence of a dominant allele of the same gene. Also, the chracter produced by a recessive gene in the homozygous state (aa).

a gene or trait that is masked by that of another gene

The form of the gene that is masked by another form in the heterozygous condition. For example, the allele for no hair on knuckles (h) is recessive to the allele for hairy knuckles (H); a person with Hh genotype has hairy knuckles. Recessive alleles are often written in lower case letters. See dominant.

A trait that is not "expressed" in the presence of a dominant trait and only determines how the offspring will develop if it is paired with another recessive trait.

Allele that determines phenotype only when homozygous; does not affect phenotype when heterozygous with a dominant allele.

A part of the gene that is only expressed if a dominant allele is not present

A trait expressed only in homozygotes.

A genetic trait that can be masked by more dominant genes. Recessive traits can be carried.

A mode of inheritance in which a gene must be present from both parents for the trait to become manifest in an offspring. See Dominant.

an allele or phenotype that is expressed only in the homozygous state.

Every cell contains two copies of each gene. Each gene contains the information for a particular gene product, such as a protein. If a gene is mutated, the gene no longer codes for the gene product. Where an individual has one gene copy or allele mutated and the other copy 'correct', the cell will only be producing half the amount of gene product. If this does not result in any disorder for the individual, the mutation is described as being hidden or 'recessive' to the correct copy of the gene. An individual with this genetic constitution is said to be a 'carrier' of a recessive gene mutation. For a recessive gene mutation to result in a particular characteristic or a disorder, both copies of the genes must be mutated (see Genetics Fact Sheet 6: Autosomal Recessive Inheritance (Mendelian Patterns of Inheritance I)).

The affects of a gene that are masked by the activity of the same gene on the other chromosome.

A condition that is expressed in homozygotes or in compound heterozygotes (i.e., those who have inherited a different disease-related allele (at the same gene locus) from each parent).

A characteristic that is unable to express itself in the cat's physical appearance in the presence of the alternate dominant characteristic.

a pattern of inheritance in which a gene mutation only causes a disease or trait when present in two copies; a recessive disease can occur with no family history. Click here to return to the passage.

Refers to an allele of a gene that is expressed when the dominant allele is not present. An allele expressed only in homozygous form, when the dominant allele is absent.

A gene that must be present in the homozygous state in order for its corresponding trait to appear.

only expresses itself phenotypically when paired with another recessive gene; its expression is obscured by the presence of a dominant gene

A trait or disorder that appears only in a child who has received two copies of the same mutant gene, one from each parent.

Describing an allele whose effect with respect to a particular trait is not evident in heterozygotes. Opposite to dominant.

See dominance.

A genetic trait that is not expressed in a heterozygous or partially heterozygous cell.

a trait that is apparent only when the gene or genes for it are inherited from both parents. See dominant, gene. senile chorea—a relatively mild and rare disorder found in elderly adults and characterized by choreic movements. It is believed by some scientists to be caused by a different gene mutation than that causing HD.

Moving back and out of view. In genetics, a recessive gene is a gene that does not express its instructions when paired with a dominant gene.

In genetics, a trait or characteristic manifested clinically with a double gene dose in autosomic chromosomes or with a single dose in males if the trait is X-linked.

a gene which contributes to the phenotype only if it is present in homozygous form. It takes two identical copies of a recessive gene to produce the trait it governs in the phenotype. In practice many genes are neither clearly dominant nor recessive, in which case geneticists speak of variable expressivity or incomplete penetrance.

mutation or disorder that is only expressed when a mutant allele it is paired in a homozygous form. It is obscured by the dominant allele in the heterozygous form.

A relative term describing the relationship of one allele to a second at the same locus when an animal heterozygous for these alleles expresses the same phenotype as an animal homozygous for the second allele. The second allele of the pair is considered dominant.

Refers to a gene that is masked unless there are two of the same gene present. In genetics these genes are denoted with lower case letters.

A trait is recessive if it is manifest only in the homozygous condition.

Referring to an altered gene which does not shows its effect if the bird carrying that gene also has an unaltered gene.

allele is obscured in the phenotype of a heterozygote by the dominant allele, often due to inactivity or absence of the product of the recessive allele.

A genetic disorder that appears only in patients who have received two copies of a mutant gene, one from each parent.[Close Window

One member of an allelic pair incapable of expression when the other (dominant) allele is present. Only if the responsible allele is carried by both members of a pair of homologous chromosomes can the recessive allele manifest itself.

A small, weaker allele is recessive.

A form of inheritance where a genetic defect causes little or no outward effect unless it is present in both of a pair of genes and has therefore been inherited from both parents. If a person has inherited one altered gene and one normal gene he or she will not be affected but will be a gene carrier. If two carriers of the same altered gene have children in each pregnancy there is a 25 percent chance that the child will inherit two copies of the altered gene and will be affected.

When different gene variations (alleles) occur at the same location (locus) on the chromosome and one of the variations (alleles) is not expressed when the other is present, the trait which is not expressed is considered recessive.

An allele which expresses itself only when present in duplicate. Recessive genes and traits are hidden or masked by dominant genes or traits.

A characteristic that is unable to express itself in the presence of the alternate dominant characteristic. See DOMINANT

A trait that is partially or completely masked by the effect of a dominant allele. The dominant A or B allele masks the presence of the recessive O allele.

The allele that will be masked and not expressed, unless there is no dominant allele present

A term applied to one member of an allele pair lacking the ability to manifest itself when the other or dominant member is present.

A genetic disorder that appears only in individuals that have received two copies of a mutant gene, one from each parent. [ Talking Glossary

An allele whose effect may be masked by its allelic (dominant) partner at the same locus. Such alleles must be present in "double dose" (homozygous) in order for their effect to be expressed in an individual.

When the traits of one gene are not expressed due to the presence of a dominant gene.

Genetic trait that appears only in people who have received two copies of a mutant gene, one from each parent.

In genetics, referring to that allele of a gene that is not expressed in the phenotype when the dominant allele is present. Also refers to the phenotype of an individual (homozygote) carrying two recessive alleles. ( Figure 8-1)