Question

a cell that contains half the usual number of chromosomes
haploid
dominant allele
trait
heredity

Explanation:

The description "a cell that contains HALF the usual number of chromosomes" matches the definition of a haploid cell. Haploid cells (like gametes) have half the chromosome number of diploid cells. "Dominant Allele" refers to a gene variant that masks others, "trait" is a characteristic, and "heredity" is the passing of traits, so they don't fit the chromosome - number - related definition.

Answer:

Haploid