The evidence that crossing over occurs at the four-stranded stage and not at the two-stranded stage of the chromosomes comes from:

The theory of recombination of linked genes due to crossing over of chromosomes during the pachytene stage of meiosis was put forward by:

Crossing over in a diploid organism is responsible for

Which of the following characteristics cannot be observed in the progeny if linkage is present?

In $Drosophila$,long wing and broad abdomen characters are dominant over vestigial wing and narrow abdomen characters. $A$ pure-breeding $Drosophila$ with long wings and broad abdomen is crossed with a pure-breeding vestigial-winged and narrow-abdomened $Drosophila$. Two of the $F_1$ individuals were crossed,and the following results were produced in the $F_2$ generation: $482$ $Drosophila$ with long wings and broad abdomen,and $154$ $Drosophila$ with vestigial wings and narrow abdomen. Which one of the following is illustrated by these results?

When the number of recombinant progeny is usually less than the number expected in independent assortment, it is called: