When normal and mutant alleles are present on opposite chromosomes of a homologous pair,the heterozygotes are called as:

Genes $A, B$,and $C$ are linked. Genes $A$ and $B$ are closer than $A$ and $C$. Find out the correct option for the given statements:
$I.$ $A$ might be before $B$ and $C$
$II.$ $B$ might be between $A$ and $C$
$III.$ $C$ might be between $A$ and $B$
$IV.$ More crossovers have occurred between $A$ and $C$ than $A$ and $B$.

State the contribution of the following scientists: Thomas Hunt Morgan and Alfred Sturtevant.

Which of the following statements is not true of two genes that show $50\%$ recombination frequency?

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?

Linked genes are separated by: