Question

Explain how a single gene effects two or more independent pathways using the example of an white eye phenotype for a fruit fly. Propose three hypothesis with details and explanation.

Answer 1

A single gene is able to show multiple effects and changes with using two or more independent pathways because in some the genes are dominant, in some recessive and in some there is slight alteration or mutation in the gene. The genes function in an organism using two or more independent pathways leading to particular phenotypic characteristics. This can at times even be determined by studying the organisms by knocking off the gene. One example is the white eye phenotype in the fruit flies.

In this it is normal for the fruit fly to have red eye which is the usual phenotype. This is one of the independent pathways that are followed by the gene that gives red eye color to the fruit fly. However in the mutant variant of the fruit fly, the eyes are brown in color. However in some it is seen that they inherit white eye which is a mutant variety. It is seen found that the wild type flies carry the gene for white allele and the white eyed flies also carry the gene for white allele. But, in the former, mostly the red eye is more dominant. The white eyed phenotype has evolved and come into picture due to some sort of mutation.

Three hypotheses            

1. Chromosome theory of Inheritance states that in different and specific location of the chromosome, genes are found and hence it shows the Mendel’s law of inheritance. This was associated with a mutation that made the color of the eyes of the fly white instead of the normal brown. It was found that it has a strong association with sex linked genes as it is inherited in different pattern in male and female.
2. The color of the eye is associated with “sex limited” inheritance pattern. The first white eyed fly was a male and when it was crossed with a normal red-eyed female, the offspring was red-eyed. This means that the white allele was recessive but on crossing the FI generation, female were red eyed but half male were white eyes. This states that in both male and female, the trait is being inherited in different pattern.
3. Principle of segregation is another hypothesis where two members of a gene pair or allele are separated from each other while forming gametes. The gametes carry one allele and other half carries the other allele. This is also one of the factors that leads to the formation of the white eyed fly due to pattern of segregation.