In genetics, AA refers to a specific type of genotype known as homozygous dominant.
Based on genetic symbols, the uppercase letter A represents a dominant allele, and the lowercase letter a represents a recessive allele. An individual inherits two alleles for each gene, one from each parent. The combination of these two alleles makes up the genotype.
Understanding the Genetic Symbols
Here's a quick breakdown of common genetic symbols:
| Symbol | Definition | Description |
|---|---|---|
| A | Dominant Allele | A version of a gene that is expressed when present. |
| a | Recessive Allele | A version of a gene that is only expressed when two copies exist. |
| AA | Homozygous Dominant | Individual has two copies of the dominant allele. |
| Aa | Heterozygous Dominant (individual has both dominant and recessive gene, but only one is expressed) | Individual has one dominant and one recessive allele. |
| aa | Homozygous Recessive | Individual has two copies of the recessive allele. |
The Significance of the AA Genotype
When an individual has the AA genotype, it means they have inherited the dominant allele (A) from both parents.
- Dominant Trait Expression: Because the dominant allele (A) is present, the trait associated with this dominant allele will be expressed. For example, if 'A' codes for brown eyes and 'a' for blue eyes, an individual with 'AA' will definitely have brown eyes.
- Purebred for the Trait: In classical genetics, a homozygous dominant individual is often considered "purebred" for that specific dominant trait, as they can only pass on the dominant allele (A) to their offspring for this particular gene.
How AA Relates to Inheritance
Understanding the AA genotype is fundamental in predicting inheritance patterns.
- When an individual with an AA genotype reproduces, they will always contribute an 'A' allele to their offspring for this specific gene.
- The offspring's genotype will then depend on the allele contributed by the other parent.
For instance:
- AA (parent 1) x aa (parent 2) = All offspring will be Aa (heterozygous dominant).
- AA (parent 1) x Aa (parent 2) = Offspring will be 50% AA and 50% Aa.
- AA (parent 1) x AA (parent 2) = All offspring will be AA.
The AA genotype represents a clear case where the dominant trait is present and guaranteed to be passed on as at least one allele (A) to all offspring.
