Biology Reference
In-Depth Information
77
[B+]:
[A-B+C-]
[A+B+C-]
[A-B+C+]
[A+B+C+]
[C+]:
[A-B-C+]
[A-B+C+]
[A+B-C+]
[A+B+C+]
Just as before, ratios are usually reported. In these studies, however, there
are only two unknowns to be determined, namely, the distance between
markers A and B, and that between B and C. We shall denote them as S and
T respectively. As a result, three-point analysis can provide very accurate
estimations of distances between genetic markers.
The equations for these ratios can be derived as follows. In order to obtain
transductants with [A+B-C+], we need a cross-over to the left of A, one
between A and B, another between B and C, and a fourth to the right of C.
Therefore, the experimentally measured number will be proportional to µ
4
.
Dividing by [A+] or [C+] both being proportional to µ
2
, we get a ratio
proportional to µ
2
. Since µ is a small number, µ
2
is negligible, usually much
less than 0.01. This finding has been used to order the three genetic
markers. Thus, among the twelve experimentally measured ratios, two
should be zero or less than 0.01. The other ten will then be functions of two
non-dimensional ratios:
