Drosophila melanogaster has $8$ chromosomes in its somatic cell. How many linkage groups will it have?

The percentage of crossing over will be more if:

Select the correct statement regarding dihybrid crosses and linkage.

There are three genes $a, b,$ and $c$. The percentage of crossing over between $a$ and $b$ is $20\%$,between $b$ and $c$ is $28\%$,and between $a$ and $c$ is $8\%$. What is the sequence of these genes on the chromosome?

Sex linkage was first observed by.....

Linkage with increasing age becomes ......