Frequency of crossing over in a chromosome is an index of

In a certain plant, red flowers $(R)$ are dominant to white flowers $(r)$ and tallness $(T)$ is dominant to dwarfness $(t)$. $A$ heterozygous plant $(RrTt)$ is backcrossed with a double recessive plant $(rrtt)$. If the gene loci for colour and size are situated very close together on the same chromosome, the expected percentage of offspring could be approximately:

Tall Red

Tall White

Dwarf Red

Dwarf White

respectively.

Drosophila has four pairs of chromosomes. How many linkage groups does it have?

Thomas Hunt Morgan was awarded the Nobel Prize for his work on:

Define/Explain the following terms:
$1.$ Linked genes
$2.$ Locus

In a test cross of a dihybrid plant with incomplete linkage,how many types of plants will be produced?