Allele
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An allele (pronounced /ˈæliːl/ (UK), /əˈliːl/ (US)) (from the Greek αλληλος allelos, meaning each other) is a member of a pair or series of different forms of a gene. When people talk about alleles, most often they mean parts of genes that are actually expressed (as part of the genotype of an individual). Sometimes though, the word is used to refer to sequences that are not expressed.
An individual's genotype is the gene that the individual will show because of the set of alleles it happens to have. In a diploid organism, two alleles make up the individual's genotype. Alleles can be represented in a Punnett square.
[change] Example
An example is the gene for blossom colour in many species of flower. A single gene controls the colour of the petals, but there may be several different versions (or alleles) of the gene.
In this example, parents have the genotype Bb (capital letters show dominant alleles and lower-case letters to show recessive alleles). If B (capital) is found in their genotype, the flower will be red. Therefore, the only time a flower is not red is when the genotype is bb (there are no capital 'B's).
| Maternal | |||
|---|---|---|---|
| B | b | ||
| Paternal | B | BB | Bb |
| b | Bb | bb | |
The probability of the flowers having different genotypes are: BB is 25%, Bb is 50%, and bb is 25%. The phenotype of the flower will always be red if a dominant B is in the genotype. Therefore, there is a 25% chance of getting a flower which is not red, and 75% chance of getting a flower which is red.
