2. G.5 pts) Research on the Folsom Fruit Fly. D folsomus, identified the pigment

Question

2. G.5 pts) Research on the Folsom Fruit Fly. D folsomus, identified the pigment that is responsible for the black color in its Based on chemical analysis of the pigment, researchers hypothesized that three enzymes were involved in synthesizing the pigment from a colorless precursor compound. Furthermore, each of the e is produced by the dominant alleles, named c r and p of their respective genes. In mating experiments with mutant flies, the following recessive alleles (and their respective phenotypes) were also identified: c (cc confers a colorless wing phenotype) r (rr confers a red wing phenotype) a) Propose and draw a detailed metabolic pathway, showing each reaction, enzyme and pigment or compound, which could account for the wild type and mutant phenotypes described above. If more than one possibility exists, choose only one and use it for part b-e below as well. b According to your proposal, describe in detail what the protein product, if any, of each of the 6 alleles does to create the 4 phenotypes observed, AND what likely causes the mutant alleles to be recessive. c) Based on your model above, which genes are epistatic to which?

Explanation / Answer

a) Lets suppose,

the enzyme encoded by c+ gene is X

the enzyme encoded by r+ gene is Y

the enzyme encoded by p+ gene is Z.

According to the question, the action of all these three enzymes on the colorless precurson compound produces black pigment in the wing. Using the information from the mutant phenotypes given by recessive alleles, a pathway can be established as follows:

Colorless precursor + X--> Red wing product + Y--> Purple wing product + Z ---> Black wing product (wild type)

cc genotype denotes the absence of the enzyme c+ i.e. X. Similarly,

rr genotype denotes the absence of the enzyme r+ i.e Yand,

pp genotype denotes the absence of the enzyme p+ i.e Z.

Now, absence of X in cc will give a colorless wing phenotype

absence of Y in rr will give a red wing phenotypes.

absence of Z in pp will give a purple wing product.

b) As mentioned the dominant genes encode for an enzyme that changes the wing color in the phenotype. Presence of atleast one dominant allele is required to code for the enzyme in order to complete the pathway to produce the wild phenotype i.e the black wing color. For example a fly with the genotype c+c would still produce the enzyme X required for the complete pathway giving black phenotype but the quantity of the enzyme produced will be less than that produced in c+c+. The mutant alleles cc, rr and pp do not code for their respective enzyme obstructing the metabolic pathway for the black pigment of the wings.

Pathway in c+c+/r+r+/p+p+

Colorless precursor + X--> Red wing product + Y--> Purple wing product + Z ---> Black wing product (wild type)

Pathway in cc

Colorless precursor + Absence of X--> Colorless wings

Pathway in rr

Colorless precursor + X--> Red wing product + Absence of Y--> Red wing phenotype

Pathway in pp

Colorless precursor + X--> Red wing product + Y--> Purple wing product + Absence of Z ---> Purple wing product.

C) Epistasis is the interaction of genes at phenotypic level to produce a particular phenotype. In simpler words, interaction of gene products to produce a particular phenotype.

A fly with all the dominant alleles as in c+c+/r+r+/p+p+ will produce black wings.

A fly with the genotype cc/r+r+/p+p+ will produce colorless wings.

A fly with the genotype c+c+/rr/p+p+ will produce red wings.

A fly with the genotype c+c+/r+r+/ppwill produce purple wings.

Therefore, r+ is epistatic to c+ whereas p+ is epistatic to r+

Related Questions

Navigate

• Browse (All)
• Browse 2
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.