Hypermedia Glossary Of Genetic Terms
|Allele||The term coined by Bateson and Saunders (1902) for characters which are alternative to one another in Mendelian inheritance (Gk. Allelon, one another; morphe, form).
Now the term allele is used for two or more alternative forms of a gene resulting in different gene products and thus different phenotypes. In a haploid set of chromosomes there is only one allele at its specific locus. Diploid organisms have 2 alleles at a given locus, i.e. a normal and a mutant allele. A single allele for each gene locus is inherited separately from each parent (e.g., at a locus for eye colour the allele might result in blue or brown eyes). An organism is homozygous for a gene if the alleles are identical, and heterozygous if they are different.
|Trait||An attribute or character of an individual within a species for which heritable differences can be defined.|
|Inheritance||Trait which is derived by an heir from an ancestor; transmission and reception by animal or plant generation. Trait acquired via biological heredity that passes from parent to offspring.|
|Gene||The term coined by Johannsen (1909) for the fundamental physical and functional unit of heredity. The word gene was derived from De Vries' term pangen, itself a derivative of the word pangenesis which Darwin (1868) had coined. A gene is an ordered sequence of nucleotides located in a particular position (locus) on a particular chromosome that encodes a specific functional product (the gene product, i.e. a protein or RNA molecule). It includes regions involved in regulation of expression and regions that code for a specific functional product. See gene expression, allele.|
|Gene product||The biochemical material, either RNA or protein, resulting from expression of a gene. The amount of gene product is used to measure how active a gene is; abnormal amounts can be correlated with disease-causing alleles.|
|Phenotype||The term coined by Johannsen (1909) for the appearance (Gk. phainein, to appear) of an organism with respect to a particular character or group of characters (physical, biochemical, and physiologic), as a result of the interaction of its genotype and its environment. Often used to define the consequences of a paticular mutation.|
|Locus||The position of a gene on a chromosome or other chromosome markers; also, the DNA at that position. The use of the term locus is sometimes restricted to main regions of DNA that are expressed. Plural: loci. See gene expression.|
|Diploid||A full set of genetic material, consisting of paired chromosomes one chromosome from each parental set. Most animal cells except the gamete have a diploid set of chromosomes. The diploid human genome has 46 chromosomes. Compare haploid and polyploid.|
|Mutation||The term which De Vries introduced into biological literature for an abrupt change of genotype which is inherited. Any permanent and heritable change in DNA sequence. Types of mutations include point mutations, deletions, insertions, and changes in number and structure of chromosomes. (Cf. polymorphism)|
|Homozygote||The term coined by Bateson and Saunders (1902) for a zygote, or a diploid individual derived from it, which carries only one member of the alleles of a gene, that is, a zygote derived from the union of gametes identical (Gk. homos, alike) in respect of a particular gene. The same allele is present at a given locus. Cf. homozygosity|
|Heterozygote||The term coined by Bateson and Saunders (1902) for a zygote, or a diploid individual derived from it, which carries both members (Gk. heteros, different) of a pair of alleles. This might occur as a result of fusion of dissimilar gametes, or from mutation. Cf. heterozygosity|
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