Question

This method only allows us to calculate distances of up to 50 map units. Phenotypes that make up more than 50% do not allow us to distinguish between linked genes more than 50 units apart and unlinked genes. The longest Drosophila chromosome is over 107 map units in length. Explain how this method can be used to construct a gene map for the entire length of the chromosome.

Answer 1

Linkage, crossing over and gene mapping is the method used to construct the map. It put into perspective recombinant frequencies.

Step-by-step explanation:

Gene linkage map – to construct a gene map for the entire length of the chromosome the following methods must be adhered to;

Step 1: Set up the genes that are the farthest apart first on the map: lets say point A and C are 49 map units apart and would be placed far apart.

Step 2: Like a puzzle solve for the position of other genes, a pencil sure will come in handy to determine the positions of interest.

Step 3: Subtraction as a function is necessary to help determine the final distances and relative distances between each gene.

Answer 2

This method can be used to construct a gene map by the maximum frequency of recombinant gametes.

Step-by-step explanation:

Let us assume 100% crossing over frequency, crossing over occurs in every cell, but only between two chromatids of the chromosomes involved.

Therefore, for single crossovers, the frequency of recombinant gametes is half the frequency of crossing over because each crossover takes place between only two of the four chromatids of a homologous pair of chromosomes so the maximum frequency of recombinant gametes is applied.