Answer:
D) the arrangement of the nucleotides within genes
Step-by-step explanation:
De-oxy ribo nucleic acid that is basically a polymer of nucleotides. Nucleotides are composed of three basic units: a de-oxyribose sugar unit, a phosphate group and nitrogenous bases that can be Adenine, Gunanine, Thymine and Cytosine.Adenine always pairs with Thymine and Guanine always pairs with Cytosine.
This is a universal composition of DNA in each and every living organism. The genes are a segment of DNA that contain specific sequence of nucleotides and encode for a specific trait of organism such as height, weight, eye color etc. The sequence of nucleotides expresses the trait in the form of protein product during the process of Translation. The products of translation are amino acids and every amino acids encode for a specific protein in almost all living organisms.
So, what differs in the specie is the sequence of nucleotides in genes. Infact this is the nucleotide sequence which brings evolution in organism and organisms evolve to form new specie with the passage of time. One major cause of change in nucleotide sequence is mutations due to which the organisms change with time.
Suppose the sequence of nucleotide of specific gene in organism A is
AAGGGGAAATTT
However in other specie organism B of same specie is:
TAGGGGAAATTT
This means only mutation of one base changed the gene in organism B and also its product called protein.
Hope it help!