Question

In a high elevation lake in Peru lives a population of guppies. There are 75 guppies in this lake, 60 of which have blue tails, while the remaining 15 have yellow tails. Tail color in guppies is controlled by a single gene. Which of the following statements about this population of guppies is true?

	Blue guppies can be either homozygous dominant or heterozygotes.
	The yellow guppies exhibit the recessive phenotype.
	Tail color in this population can evolve.
	All of these statements are true.

Answer 1

This question is an example of mendelian trait: This is an example of monohybrid cross i.e single gene is controlling the trait.

Let us assume that the dominant genotype of this trait is TT, which is responsible for blue colour tail of the guppies and recessive genotype is tt, which is responsible for yellow tail of the guppies. The phenotypic ratio of these types of monohybrid crosses are 3:1, i.e. 3 out of 4 guppies will be showing blue tail and 1 out of 4 will be showing yellow tail.

1.So being dominant (blue colour tail) can be possible if the genotype is either homozygous dominant (TT) or heterozygotes (Tt). As a single dominant allele is sufficient to show the dominant phenotype according to the law of dominance by Mendel. (Option one is true)

For the calculation of all Dominant phenotype in the population = 3/4 * 75

                                    = 56.25 (which is near to 60) as observed frequency is always approximate

For the calculation of all recessive phenotype = 1/4 * 75

                                                                         = 18.75 (which is near to 15)

2. Being present in low number in the population yellow guppies must be recessive phenotype (Option two is also true)

3. As in the natural environment, the population is always in some kind of selection pressure. So there is always a possibility to evolve. (Option three is also true)

4. The correct answer is option four, as all the statements are correct