Two genes lie 3 Mb apart on human chromosome 2 On average th

Two genes lie 3 Mb apart on human chromosome 2. On average, the map distance between these loci would be 3 cM. Under what circumstances might the map distance be considerably larger or smaller than 3 cM? Explain your answer.

Solution

The circumstances under which the map distance can considerably vary are only if some sort of chromosomal aberrations occurs. The chromosomal aberrations that could alter map distance are:

Duplication

Translocation and

Deletion.

The map distance can considerably increase in case of translocation or duplication of chromosome.

In duplication a gene sequence get duplicated several times and if this happens to the genes which lie between above mentioned loci the it would lead to increase in the map distance, similarly if an broken part of a chromosome somehow manages to insert itself in between the above mentioned loci , the also it will lead to an increase in map distance .

However the map distance can only decrease if deletion occurs between the said genes leading to a lose of few gene in between, leading to a decrease in the map distance