Here's why:
* Genes come in pairs: Each organism inherits two copies of each gene, one from each parent.
* Different versions of a gene (alleles): These two copies might be the same or different versions of the gene, called alleles.
* Dominant and recessive alleles: One allele might be "dominant" and mask the expression of the other, "recessive" allele.
Example:
* Let's say the gene for eye color has two alleles: brown (B) and blue (b).
* Brown is dominant, meaning if someone inherits at least one "B" allele, they will have brown eyes.
* Blue is recessive, meaning someone needs to inherit two copies of the "b" allele to have blue eyes (bb).
In this case, an individual with the genotype Bb (one brown and one blue allele) will have brown eyes because the dominant brown allele masks the expression of the recessive blue allele.
Key Point: The recessive trait will only be expressed when an individual inherits two copies of the recessive allele.
