Researchers have found a population of blind cave salamanders and would like to

Question

Researchers have found a population of blind cave salamanders and would like to know

which gene has been mutated to cause the loss of sight. They have generated an F2

mapping population by crossing a blind cave individual with an individual from a closely

related population that inhabits open streams (and can still see). The researchers observe

a 3:1 ratio of sighted to blind salamanders in the F2s from this cross and conclude that

blindness is recessive and caused by a single gene. By genotyping blind individuals from

the F2 mapping population, they have narrowed down the location of the gene and

obtained the following data for 7 markers in this region. For each marker, “Hom”

indicates that the individual is homozygous for the “cave” allele, and “Het” indicates that

the individual is heterozygous (one “cave” allele and one “open stream” allele).

a) The gene responsible for blindness must be between markers #___ and #___.

[Provide the narrowest possible window that correctly completes this statement.

Briefly explain the logic you used to narrow down the location of the gene to

being between these markers.]

b)

To further narrow down the window for the gene, would it be more important in

this particular scenario for the researchers to genotype more blind F2 individuals

or to generate more markers? In your answer, describe how the data and the

spacing of the markers led you to your conclusion

Explanation / Answer

a) The gene responsible for blindness must be between markers # 6-7 and # 1-2.

This is due to the fact that marker #3-5 are common in all the scenarios and thus this indicates that they play the least/ no part in this case and therfore the gene must actually be present in between marker 6 and 7, as the variation here leads to 6 F2 progeny in the 2nd genotype and 1 F2 individual in the 3rd genotype.

And the variation in between markers 1 and 2 leas to variation where their are 1 F2 progeny in the 4th genotype and 4 F2 progeny in the 5th genotype.

b) Pertaining to this case, it is more important to generate more markers betwenn markers 1 and 2 and markers 6 and 7.

This will lead to specific narrowing down of the loci of the gene in question.

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