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Occurrence
An allele is an inherent or naturally-occurring gene that already occupies a specific position in a chromosome. In humans, 23 pairs of chromosomes are inherited, with one from each pair coming from each of the parents. Chromosomes pair up according to the inherited gene or trait they are coded for. For instance, a chromosome for eye color from one parent will pair up with a matching eye color chromosome from the other parent. Sometimes, the genetic trait may not be identical in the two chromosomes. For example, one parent has brown eyes and the other has green eyes. On the other hand, a transgene is an extrinsic gene, as it is introduced into a parent chromosome to modify certain characteristics in the offspring. Although such a gene is still coded for the same trait, it's possible that a transgene comes from a different host other than the parents.
Expression of a Genetic Trait
There is always a dominant and a recessive gene in allelic pairing of chromosomes. As its name suggests, a dominant gene is expressed in the offspring -- it is the trait that progeny exhibits. On the other hand, a recessive gene is not transcribed in the offspring -- it is unexpressed. In contrast, a transgene is programmed to be ultimately transcribed in progeny, which means that transgenes are always dominant.
Characteristics
Alleles are part of the natural process when individual deoxyribonucleic acid (DNA) forms. When two alleles or traits are of the same kind (both parents have the same trait), then the organism has a homozygous gene, but when the individual possesses two different traits (one dominant and one recessive), then the organism has a heterozygous gene. Transgenes are altered genes that have a modified DNA. They do not naturally occur, and they are always designed to be the dominant gene that will manifest when the organism develops.
Uses of Study
Allele investigations are done to determine which part of the genetic makeup of individuals causes complications, such as disorders and diseases; in population index studies wherein allele frequency in a certain population is studied to see how and why a specific quality appears in members of that population. They are also used in identity testing and for human evolution studies. Transgenic procedures are done to produce organisms with certain traits that can be resistant to or prone to known diseases, to trace disease patterns or instigate treatment investigations, and to produce economically higher yielding breeds.