A sex-linked trait a Is determined by an allele on a sex chromosome
b Always affects biologically female offspring
c Connects fragments of DNA from different sources
d Is always a dominant trait

So probably the answer is A

Explanation:

A particularly important category of genetic linkage has to do with the X and Y sex chromosomes. These not only carry the genes that determine male and female traits but also those for some other characteristics as well. Genes that are carried by either sex chromosome are said to be sex linked.

Men normally have an X and a Y combination of sex chromosomes, while women have two X's. Since only men inherit Y chromosomes, they are the only ones to inherit Y-linked traits. Men and women can get the X-linked ones since both inherit X chromosomes.

that scientist would be robert hooke