* Alleles: These are alternate forms of a gene that occupy the same position (locus) on a chromosome. For example, a gene for eye color might have two alleles: one for blue eyes and one for brown eyes.
* Recessive Allele: A recessive allele is one that only expresses its trait if two copies of it are present. It is "masked" by the dominant allele if present.
* Dominant Allele: A dominant allele expresses its trait even if only one copy is present.
Example:
Imagine the gene for eye color has two alleles:
* B: Brown eyes (dominant)
* b: Blue eyes (recessive)
Here's how the combinations work:
* BB: Brown eyes (two dominant alleles)
* Bb: Brown eyes (one dominant, one recessive)
* bb: Blue eyes (two recessive alleles)
In this example, a person needs to inherit two blue eye alleles (bb) to have blue eyes. If they inherit one brown eye allele (B), they will have brown eyes regardless of whether the second allele is brown (B) or blue (b).
Key Points about Recessive Traits:
* Hidden: Recessive traits are often hidden in a person's genotype (genetic makeup) but not expressed in their phenotype.
* Carrier: A person who has one dominant and one recessive allele is a carrier for the recessive trait. They do not express the trait themselves but can pass it on to their children.
* Probability: There is a 25% chance that two carriers of a recessive trait will have a child who expresses the trait.
Many genetic disorders, like cystic fibrosis and sickle cell anemia, are caused by recessive alleles. This means that both parents must carry the recessive allele for their child to inherit the disorder.
