23. Each trait has two alleles. How many alleles would have to be a dominant allele for the offspring to express a dominant trait

One (1) of the alleles

Explanation:

According to Gregor Mendel in his series of experiments, he discovered that two forms of a gene called ALLELE contributed to the formation of a trait. However, in his law of dominance, Mendel stated that one allele called the DOMINANT ALLELE has the ability to mask the phenotypic expression of the other allele called RECESSIVE ALLELE when present.

This means that, in a combination of both alleles in a gene (heterozygous), only one allele coding for a phenotypic characteristics will be expressed. This phenotype is called the DOMINANT TRAIT.

For example, if tall allele (T) is dominant over the short allele (t), the tall trait will be expressed when the genotype is "Tt" meaning that only one of the alleles would have to be a dominant allele for the offspring to express a dominant trait.