Linkage mapping

Question 1

When building a linkage map, is it easier to use three or two loci?

Answer 1

Three

Question 2

What were the three traits used to illustrate the three-point cross?

Answer 2

Scute (loss of bristles), echinus (rough eye), and crossveinless wings

Question 3

What traits were used to illustrate multiple crossovers?

Answer 3

Crossveinless wings, snipped wings, and vermillion eyes

Question 4

What is the use of double crossovers in mapping?

Answer 4

It allows order to be established

Question 5

What is the main limitation of three-point crosses?

Answer 5

It cannot distinguish between 1, 3, 5, odd number of crossover events, therefore can only be used over short segments where only 1 crossover is likely to happen

Question 6

Is linkage mapping still relevant?

Answer 6

Yes, mostly replaced by physical mapping, but still important for searching down genes of commercial interest

Question 7

Many of the traits Mendel claimed were independently assorted were actually on the same chromosome, how can this be explained?

Answer 7

Loci far enough apart on the same chromosome will recombine at frequencies that are essentially free

Question 8

What is the coefficient of interference?

Answer 8

A measure of how one chiasma forming prevents another nearby chiasma from forming–effectively, discrepancy between expected and observed double-crossovers