Homologous recombination occurs in a heterozygote in which alleles D and d differ by a single base pair. The D allele has a G at one position, whereas the d allele has a C at the same position. If branch migration causes heteroduplex formation across this position, what is the expected outcome

The DNA repair pathway will recognize the mismatch (G-G) to convert guanine to cytosine (C), thus reverting the DNA sequence to the d allele

Explanation:

DNA repair pathways correct mismatches that can arise during DNA replication and recombination, which can be naturally caused or as consequence of mutagenic treatments (for instance, exposure to UV light). However, these pathways are not always efficient and there are occasions that mismatches escape from the mechanisms of correction. If these mismatches occur in gametic cells, mutations could be fixed in the next generation. The base mismatch repair mechanism during recombination is known as 'gene conversion', since this process produces the conversion of one allele to other as result of an inappropriate base mismatch.

answer: substrate concentration. enzymes work best when there is a high enough substrate concentration for the reaction they catalyse.