How many double-helical DNA molecules will be present in the sperm and egg cells of dogs that are diploid animals that contain 78 replicated chromosomes in each cell that enters meiosis?

39 double-helical DNA molecules will be presenet in sperm and 39 in egg.

Explanation:

Each chromosome is made up of histone protein and a molecule of DNA.

Each cell contain double number of chromosomes (2n) except a few exceptions like sperm (1n) and egg (1n).

Human body cells contain 46 chromosomes while sex cells contain 23 chromosomes because of meiosis. Similarly dog cells contain 78 chromosomes while their gametes i. e egg and sperm each contain 39 chromosomes. The fertilization of sperm and egg will restore the chromosome numbers.

As there is only one double helix DNA present in chromosome, so there would by 39 double helix DNA in sperm and 39 double helix DNA in egg.