For an offspring to what a recessive trait, both parents must have at least one what allele in their genotype

For an offspring to have a recessive trait, both parents must have at least one recessive allele in their genotype

Explanation:

When an organism contains a pair of dissimilar alleles for a given trait it is said to be heterozygous. A heterozygous state contains one dominant  allele and a recessive allele. When two parents are heterozygous, the offspring will have a recessive trait. For example a cross between heterozygous tall plants.

      T           t

T     TT         Tt  

t     Tt           tt

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enzyme active site and substrate specificity

enzymes bind with chemical reactants called substrates. there may be one or more substrates for each type of enzyme, depending on the particular chemical reaction. in some reactions, a single-reactant substrate is broken down into multiple products