Final answer:
In the species of insects with variable chromosome numbers, individuals with 17 chromosomes are males, and those with 18 chromosomes are females. This variation is similar to the genetic XY sex-determination system observed in mammals and some insects. Therefore, the correct option is A.
Step-by-step explanation:
In a certain species of insects, some individuals have 17 and some have 18 chromosomes. The 17 and 18 chromosomes bearing individuals are males and females respectively. This difference in chromosome count is related to sexual differentiation within the species, analogous to the XY sex-determination system found in mammals and some insects, where the presence or absence of the Y chromosome determines the sex of the individual. In mammals, individuals with XX chromosomes are female, while those with XY chromosomes are male. Pioneering scientist Nettie Stevens observed these chromosomal differences and played a crucial role in our understanding of genetic sex determination. The variation in chromosome number in this insect species likely represents a similar mechanism of sex determination.