Genetic Linkage and Recombination — NEET Biology
✅ Asked in NEET 2016Morgan and his group knew that the genes were located on the X chromosome (Section 4.4) and saw quickly that when the two genes in a dihybrid cross were situated on the same chromosome, the proportion of parental gene combinations were much higher than the non-parental type. Morgan attributed this due to the physical association or linkage of the two genes and coined the term linkage to describe this physical association of genes on a chromosome and the term recombination to describe the generation of non-parental gene combinations. Morgan and his group also found that even when genes were grouped on the same chromosome, some genes were very tightly linked (showed very low recombination) while others were loosely linked (showed higher recombination). For example he found that the genes white and yellow were very tightly linked and showed only 1.3 per cent recombination while white and miniature wing showed 37.2 per cent recombination. His student Alfred Sturtevant used the frequency of recombination between gene pairs on the same chromosome as a measure of the distance between genes and 'mapped' their position on the chromosome. Today genetic maps
Linkage is the physical association of genes on the same chromosome that produces more parental than non-parental combinations in crosses. The NTA tests whether you understand that genes on the same chromosome don't assort independently—they tend to stay together, limiting recombination. Students often confuse linkage with independent assortment and expect 1:1:1:1 ratios even for linked genes. Remember: tightly linked genes show low recombination frequency (parental types dominate), while loosely linked genes show higher recombination. The recombination frequency percentage equals the map distance in centiMorgans, which Sturtevant used to create genetic maps.
In a test cross involving F₁ dihybrid flies, more parental-type offspring were produced than the recombinant-type offspring. This indicates: (NEET 2016 Phase 1)
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