please explain the figure of linkage i.e., fig.5.11 in NCERT on page no. 84.
These two crosses explain about linkage.
Cross A shows less recombination frequency because two genes(y and w) are tightly linked and located on the same chromosome, the proportions of parental gene combinations are much higher than those of non-parental.
Cross B shows high recombination frequency two genes ((w and m) are loosely linked.
If crossing over does not occur, the products are parental gametes. If crossing over occurs, the products are recombinant gametes( non parental).
Alleles tightly linked and present on same chromosome have higher chances of staying together as they have no chances of separating by crossing over and are always transmitted together.
Alfred Sturtevant utilised the knowledge of frequency of gene recombination as a measure of physical distance between two genes and to map their position on chromosomes.
in body colour: dominant traits or wild type are written as+sign with them as ( y+) and it is for brown body like wise red eye and normal wings are dominant. whereas recessive traits are yellow body white eye and miniature wing. these points u must remember to understand it. seconds are d principals of linkages