How are alleles related to dominance and recessiveness?

• A. They are combinations of multiple genes
• B. They are variants of a single gene
• C. They determine the energy level of a cell
• D. They act independently of the organism's environment

Answer: (B)

Alleles are indeed variants of a single gene, which means they occupy the same locus on homologous chromosomes but may have different sequences or traits associated with them. This genetic variability is essential for understanding dominance and recessiveness in inheritance. When an individual has two different alleles for a particular gene, one may mask the expression of the other; the dominant allele will determine the observable trait, while the recessive allele will not express its effect unless an individual has two copies of it.

Understanding how alleles function in terms of dominance and recessiveness provides valuable insight into the fundamental principles of genetics, including how traits are inherited, the relationship between genotype (the genetic makeup) and phenotype (the observable traits), and how genetic diversity contributes to evolution.