Question

7. Back at your Hogwarts Genetics internship, you are working with Hagrid studying a
population of blast-ended skrewts. The skrewts can be blue, green, or orange. Hagrid has been
picking random skrewts from the population to cross with each other. He is confused by the
results.
Below is the data for five crosses done with individual skrewts from the population, and the
progeny from each cross.
a. Describe a model for the genetic basis of skrewt body color in the Hogwarts skrewt
population.
b. Following your model, for each cross, write the genotypes of all parents and progeny as
completely as possible. Make up any gene symbols you need.
Write out all of your work so that we can follow your train of thought. (14 points)

Cross Parents Progeny (offspring)
1 blue x blue 3⁄4 blue : 1⁄4 orange
2 green x green 3⁄4 green : 1⁄4 orange
3 blue x blue 3⁄4 blue : 1⁄4 green
4 blue x green 6/16 blue : 6/16 green : 4/16 orange
5 orange x orange All orange

Answer 1

a.

The genetic basis of skrewts body color in Hogwarts skrewts is showing Epistasis.

Epistasis is a phenomenon in which, the phenotype of one gene locus masks the phenotype of a second gene locus.

b.

Here, Blue body color is dominant and it masks all other colors. When Dominant allele B present in the genotype, the body color will be blue. A single dominant allele is sufficient to express the blue phenotype.  When the recessive allele,  b present at both the locus it can not masks the effect of other gene.

Green coloration occurs due to another dominant allele G.

When all the alleles are recessive the phenotype is orange.  

B_gg , B_Gg, B_GG = Blue color

bbGg, bbGG = Green color

bbgg = Orange

Cross1.

Cross2.

Cross 3.

Cross 4.

The given ratio is not possible.

Cross 5.