What is true about sex chromosomes that can influence phenotype?

Sex chromosomes, specifically X and Y chromosomes in many organisms (including humans), play a significant role in determining an individual's phenotype, but the relationship is not always straightforward. The correct assertion is that they can sometimes not match the observed phenotype due to various reasons, such as gene expression, environmental influences, or the presence of mutations.

For example, in individuals with XX chromosomes, one might expect a typical female phenotype, but factors such as hormonal environment or the presence of specific genetic conditions can lead to variations in physical traits. Similarly, individuals with XY chromosomes who are genetically male might exhibit intersex traits due to differences in how sex-determining genes are expressed.

This complexity underscores that while sex chromosomes contribute to the development of certain physical traits, they do not solely dictate them. Other genetic and environmental factors intertwine with sex-linked genes, leading to phenotypic diversity that may not neatly align with chromosomal composition.