Final answer:
The chromosomes that differ between males and females are known as sex chromosomes. These chromosomes are X and Y, where females have XX and males have XY, determining their genetic sex. The study of sex-linked traits and the variations in sex chromosomes were first observed by Nettie Stevens.
Step-by-step explanation:
Chromosomes that differ between males and females are called sex chromosomes. In humans, females possess two X chromosomes (XX), while males have an X and a Y chromosome (XY), which dictates their sex. The X chromosome is significant in length and contains a large number of genes, whereas the Y chromosome is much shorter and has fewer genes.
Nettie Stevens was a pioneering scientist who first observed these chromosomal differences between sexes by studying mealworms. The sex chromosomes determine the genetic sex of an individual, with the presence of a Y chromosome resulting in male characteristics and its absence resulting in female characteristics. Human males are therefore considered heterogametic, with two different sex chromosomes (XY), and females are homogametic, with two of the same type of sex chromosome (XX).