A(n) is one of the 46 molecules of DNA (in 23 pairs) that virtually every cell of the human body contains and that, together, contain all the genes.

Chromosome

Explanation:

Every cell in a human body contains the same genetic material (DNA), which holds the information needed for the organisms optimal functioning on genes. However, these DNA, which are 46 (23 pairs) in number in humans are found as long visible X-shaped structures called CHROMOSOMES.

Originally, DNA is a long strand of nuceleotide and due to this it becomes difficult to fit into the nucleus of the cell. The cell, however, devises a means to make its genetic material contain its nucleus by wrapping the long DNA around certain proteins called HISTONES. These histone-DNA complex forms the Chromatin, which is later compacted and further coiled to form the CHROMOSOME.

explanation:

the fossil record extends back to a dog-like ancestor some 55 million years ago, which gave rise to the first horse-like species 55 to 42 million years ago in the genus eohippus.