Final answer:
The least useful trait for cladistic analysis when constructing a phylogenetic tree would be the a) color of fur, as it can change due to environmental factors and does not necessarily reflect evolutionary relationships like homologous traits do.
Step-by-step explanation:
When constructing a phylogenetic tree with cladistic analysis, choosing traits that reflect evolutionary relationships is crucial.
The least useful trait among the options provided for this purpose would be (a) The color of fur since fur color can be subject to environmental influence and can change quickly and independently in different species, known as an analogous characteristic.
In contrast, traits like the number of limbs are more likely to be homologous, being inherited from a common ancestor, and less likely to change independently in related species.
After cladistics has been applied to determine ancestor-descendant relationships using homologous characteristics,
a phylogenetic tree can reveal the points in time where different species diverged from common ancestors.
This helps to illustrate the evolutionary history of the species, an important concept in biology, allowing us to better understand the genetic and evolutionary relationships between different organisms