Final answer:
The question seems to reference the physical traits of a character. Trait variation refers to the differences in physical appearance that may be influenced by genetic factors like X-linked genes. Specific physical traits such as youth, lack of a beard, or posture can help distinguish and characterize individuals in literature.
Step-by-step explanation:
It seems there is a slight misunderstanding in the student's question, as it appears to reference the physical traits of a character not named Jonas, which makes it difficult to provide an accurate answer. However, speaking in general terms about trait variation, this refers to differences in the physical appearance of a heritable characteristic, which can be influenced by an X-linked gene present on the X chromosome but not on the Y chromosome.
Descriptions of characters, like the one Steven points to— a young, beardless figure with curly hair—are often included in literary works to help readers visualize and distinguish characters. Likewise, the posture of a character such as being hunched over as mentioned by Beth can also be a distinguishable trait that adds depth to a character's portrayal.