Describe the dihybrid cross carried on Drosophila melanogaster by Morgan and his group.
How did they explain linkage, recombination and gene mapping on the basis of their
observations ?
Dear student,
Thomas Hunt Morgan discovered the basis of variations that sexual reproduction produced. He worked on fruit flies, Drosophila melanogaster. He chose Drosophila because of the following reasons:
Morgan’s experiment
Explanation of deviation from Mendelian ratio:
From the above diagram, the gametes formed from F1 individuals are clearly shown in the above diagram. These gametes include:
Brown bodied Red eyed (y+ w +)
Brown bodied White eyed (y+w)
Yellow bodied White eyed (yw)
Yellow bodied Red eyed (yw+)
Mapping of gene was conducted by Sturtevant, student of Morgan. The presence of linked gene affected the the offspring in next generation. So, frequency of genetic recombination was calculated by the position of linked gene on the chromosome. This method was termed gene mapping.
Regards
Thomas Hunt Morgan discovered the basis of variations that sexual reproduction produced. He worked on fruit flies, Drosophila melanogaster. He chose Drosophila because of the following reasons:
Morgan’s experiment
- Dihybrid cross was carried out on fruit flies. Yellow bodied, white eyed females were crossed with brown bodied, red eyed males.
- F1 progeny was obtained, which were inter-crossed.
- F2 progeny was obtained and F2 ratio was observed.
- F2 ratio was observed to be significantly different from 9:3:3:1 as observed in Mendelian dihybrid cross.
Explanation of deviation from Mendelian ratio:
- Genes involved are located on X chromosome.
- When two genes are located on the same chromosome, the proportions of parental gene combinations were much higher than those of non-parental.
- Linkage − Physical association of genes on a chromosome
- Recombination − Non-parental gene combination.
From the above diagram, the gametes formed from F1 individuals are clearly shown in the above diagram. These gametes include:
Brown bodied Red eyed (y+ w +)
Brown bodied White eyed (y+w)
Yellow bodied White eyed (yw)
Yellow bodied Red eyed (yw+)
Mapping of gene was conducted by Sturtevant, student of Morgan. The presence of linked gene affected the the offspring in next generation. So, frequency of genetic recombination was calculated by the position of linked gene on the chromosome. This method was termed gene mapping.
Regards