What are the conclusions drawn by T.H. Morgan from the crossing experiment in Drosophila with respect to linkage?

The conclusions drawn by T.H. Morgan from the crossing experiment in Drosophila with respect to linkage were-

1) The gene responsible for eye colour is located on X chromosome.

2) The alleles responsible for eye colour are present on X chromosome.

3) There are two X chromosomes in females. Both X chromosomes carry an allele of the trait.

4) Females can be homozygous or heterozygous for the alleles.