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प्रश्न
Answer the following question.
Explain linkage and recombination as put forth by T.H. Morgan based on his observations with the Drosophila melanogaster crossing experiment.
उत्तर
The linkage is a term that describes the tendency of certain loci or alleles to be inherited together. Genetic loci on the same chromosome are physically close to one another and tend to stay together during meiosis, thus are genetically linked. Genetic recombination is the formation of new combinations of alleles in offspring as a result of the exchange of DNA sequences between chromosomes. It occurs naturally, as in sexual reproduction during meiosis or artificially, as a result of experiments on genetic engineering.
Thomas Hunt Morgan and his colleagues used the fruit fly, or Drosophila melanogaster to study linkage. They showed how sexual reproduction gave rise to variations. Similar to Mendel’s dihybrid cross in peas, Morgan conducted a dihybrid cross between yellow-bodied, white-eyed females and brown-bodied, red-eyed males. Shockingly, the self-crossing of F1 generation did not give a ratio of 9: 3: 3: 1 in the F2 generation. The result showed a deviation from Mendel’s dihybrid cross.
Morgan observed that while crossing a set of characteristics, two genes did not segregate as per Mendel’s law. If two genes were present on the same chromosome, the probability of getting a parental combination was much higher in the next generation as compared to the non-parental combination. This physical association of genes was termed as linkage.
In addition, they noted that the probability recombination is dependent on how strong the linkage is. In other words, though there is a link between two genes on chromosomes, genes may or may not be tightly linked. Some genes have strong linkage giving less chance of recombination while another linkage of genes is weak (loosely linked) giving a higher chance of recombination.
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संबंधित प्रश्न
Which of the following is NOT an example of connecting link?
- Archaeopteryx
- fchthyostegia
- Seymouria
- Biston betularia
What is criss-cross inheritance?
Write the scientific name of the organism Thomas Hunt Morgan and his colleagues worked with for their experiments. Explain the correlation between linkage and recombination with respect to genes as studied by them.
Answer the following question.
Explain linkage and recombination as put forth by T.H. Morgan based on his observations with the Drosophila melanogaster crossing experiment.
Write a note on sex linkage.
When a white eye Drosophila male (Xr Y) is crossed to a red eye female (XR XR), in the F2 generation all the females are red eyed and 50% males are white eyed. In a criss-cross test, when males are white eyed. In a criss-cross test, when a white eyed female (Xr Xr) is crossed to a red eye male (XRY), the F1 generation offspring had white eyed males while the female offspring bad red eyes. Instead of crossing of a white eyed female (Xr Xr} to a red eyed male (XRY), white eye female (XrXr) to white eye male (XrY) is crossed, the F1 generation will have the following phenotypes and genotype.
Analyse the following statements with respect to complete sex linkage and select the correct option.
- It is exhibited by genes located on non-homologous regions of X and Y chromosomes
- Y-linked trait is hypertrichosis.
- X-linked traits are haemophilia, red-green colour blindness, myopia (near sightedness).
The distance between the genes is measured by ______.
Which of the following is suitable for experiment on linkage?
Linkage groups can be separated during ______ in meiosis.
