In order to determine how to build a cladograms scientists don't rely solely on the physical characteristics. The most frequent way that scientists determine the closeness of a relationship is through the study of an organism's genome. Using 3-4 sentences, example what makes an organism's genome the best source of data for creating a cladogram.

See explanation below.

Explanation:

Today that technology has improved significantly, cladograms can be constructed based on molecular evidence instead of the physical characteristics. This has made this process easier and more reliable due to different reasons, among them we can state that:

1. Constructing cladograms with molecular sequences, such as amino acid sequences, is more accesible as online databases like Genbank provide reliable DNA sequences of numerous organisms that are backed up by researchers. This method can then allow a researcher to compare differences or similarities between the selected species.

2. New softwares are capable of comparing DNA sequences for similarities and differences between selected species as species that are closely related should have a higher degree of similarity in their sequence.

3. In comparison to feature-based cladograms, softwares that generate molecular cladograms possess several algorithms that are able to identify the best and more reliable cladogram.

4. Another advantage is that molecular cladograms are cheaper and, certainly, analyzing physical differences is much less reliable and could have more bias than DNA sequence analysis.