RNA molecules attach to codons when the ribosome reaches the start codon.
Explanation:
The start codon initiates translation of the mRNA by the ribosome into a polypeptide. When the ribosome finds the start codon, it attaches to the mRNA and the first amino acid, methionine, is recruited. The ribosome then continues translating the rest of the mRNA until it encounters a stop codon that initiates the ‘knocking off of the ribosome from the mRNA.
It is given that the allele B for the black coat is dominant over allele b for a brown coat.
A dominant allele always leads to the expression of the dominant trait in the heterozygous condition.
When a black and brown horse is crossed as given in the question and the result is a brown foal, then the genotype of the brown foal must be bb as the brown coat is a recessive trait.
Since each parent contributes one allele each for a given gene, the black horse must have b allele, and hence must be heterozygous Bb.
