Morgan and his group observed that when genes are grouped on the same chromosome,some genes are very tightly linked and show:

Thomas Hunt Morgan worked on which of the following organisms?

When a group of genes exhibits linkage,they:

In $Neurospora$,the arrangement of $8$ ascospores produced is $2a : 4a : 2a$. This indicates:

Who mapped the position of genes on chromosomes by using the frequency of recombination between gene pairs on the same chromosome as a measure of the distance between genes?

. . . . . . $(B)$ . . . . . . used the frequency of recombination between gene pairs on the . . . . . . $(A)$ . . . . . . as a measure of the distance between genes and mapped their position on the chromosome.
$(A) \quad\quad (B)$