안녕하세요 ^^
double cross over 때문에 그렇습니다. A와 B 사이에 cross over 가 일어났고, B 와 C 사이에 cross over 가 일어났다면, A 와 C 사이는 결국 같은 chromosome에 위치하게 되는 거니 둘사이는
cross over 한게 아닌 셈이 되는거라서,, A B 사이에 cross over freq + B C 사이에 corss over freq 가 A C 사이의 cross over freq 보다 조금 높아지게 됩니다. 아래 그림 참고하시고 아래 글 읽어보세요 ^^
칸 아카데미에서 가지고 왔습니다.
Double crossovers are "invisible" if we're only monitoring two genes, in that they put the original two genes back on the same chromosome (but with a swapped-out bit in the middle). For example, the double crossover shown above wouldn't be detectable if we were just looking at genes A and C, since these genes end up back in their original configuration.
Because of this, double crossovers are not counted in the directly measured recombination frequency, resulting a slight underestimate of the actual number of recombination events. This is why, in the example below, the recombination frequency directly measured between A and C is a bit smaller than the sum of the recombination frequencies between A-B and B-C. When B is included, double crossovers between A and C can be detected and accounted for.
