Question

A geneticist from an alien planet that prohibits genetic research brought with him two true-breeding lines of frogs. One frog line croaks by uttering "rib-it rib-it" and has purple eyes. The other frog line croaks by muttering "knee- deep knee-deep" and has green eyes. He mated the two frog lines, producing \(F_{1}\) frogs that were all utterers with blue eyes. A large \(\mathrm{F}_{2}\) generation then yielded the following ratios: \(27 / 64\) blue, utterer \(12 / 64\) green, utterer \(9 / 64\) blue, mutterer \(9 / 64\) purple, utterer \(4 / 64\) green, mutterer \(3 / 64\) purple, mutterer (a) How many total gene pairs are involved in the inheritance of both eye color and croaking? (b) Of these, how many control eye color, and how many control croaking? (c) Assign gene symbols for all phenotypes, and indicate the genotypes of the \(P_{1}, F_{1},\) and \(F_{2}\) frogs. (d) After many years, the frog geneticist isolated true-breeding lines of all six \(\mathrm{F}_{2}\) phenotypes. Indicate the \(\mathrm{F}_{1}\) and \(\mathrm{F}_{2}\) phenotypic ratios of a cross between a blue, mutterer and a purple, utterer.

Short answer

Based on the analysis and solution, we can summarize the answers to the questions as follows: a) There are 2 total gene pairs involved in the inheritance of both eye color and croaking in frogs. b) 1 gene pair controls eye color, with alleles B (blue), G (green), and P (purple), and 1 gene pair controls croaking, with alleles U (utterer) and M (mutterer). In the F1 generation, all frogs have the genotype BbUu, meaning they are blue-eyed utterers. In the F2 generation, there are 6 different phenotypes with their respective genotypes, as indicated in Step 3. When crossing a blue-eyed, mutterer frog with a purple-eyed, utterer frog, the expected phenotypic ratios of the F2 offspring are: - 9/16 blue-eyed, utterer - 3/16 green-eyed, utterer - 3/16 blue-eyed, mutterer - 1/16 purple-eyed, utterer

Step-by-step solution

Observe the phenotypic ratios in the F2 generation

The ratios of frogs in the F2 generation are given as follows: - 27/64 blue, utterer - 12/64 green, utterer - 09/64 blue, mutterer - 09/64 purple, utterer - 04/64 green, mutterer - 03/64 purple, mutterer We can see that these numbers are close to multiples of 3, so this suggests that the inheritance is a result of two gene pairs, each with two alleles (dihybrid inheritance).

Determine the number of gene pairs involved

There are two traits in consideration: eye color and croaking. We can infer that there are three possible eye colors (blue, green, and purple) and two types of croaking (utterer and mutterer), which are determined by two gene pairs. So, the answer to (a) is 2 total gene pairs involved in the inheritance of both eye color and croaking. Now we need to determine how many of these pairs control eye color and croaking separately: - Eye color phenotypes: blue, green, and purple (determined by 1 gene pair) - Croaking phenotypes: utterer and mutterer (determined by 1 gene pair) The answer to (b) is 1 gene pair for eye color and 1 gene pair for croaking.

Assign gene symbols and identify genotypes

We will use the following symbols to represent the traits: - Eye color: B = blue, G = green, P = purple (uppercase = dominant) - Croaking: U = utterer, M = mutterer (uppercase = dominant) Next, we can identify the genotypes of the P1, F1, and F2 frogs: - P1 (rib-it, purple-eyed): PPUU - P1 (knee-deep, green-eyed): GGMM - F1 (all blue-eyed utterers): BbUu In the F2 generation, we have the following phenotypes and genotypes: - 27/64 blue-eyed, utterer (BBUU, BBUu, BbUU) - 12/64 green-eyed, utterer (BbUu, bbUU, BbUu) - 09/64 blue-eyed, mutterer (BBuu, BBuU, BbUu) - 09/64 purple-eyed, utterer (PPUU, PPUU, PPUu) - 04/64 green-eyed, mutterer (Bbuu, bbUu, bbUu) - 03/64 purple-eyed, mutterer (PPUu, PPuu, PPuu) F2 genotypes are given above in the parentheses (in any order).

Calculate F1 and F2 phenotypic ratios for a specific cross

We are asked to cross a blue-eyed, mutterer frog with a purple-eyed, utterer frog. From the F2 genotypes, we can identify the possible genotypes for these: - Blue-eyed, mutterer: BBuu, BBuU, BbUu - Purple-eyed, utterer: PPUU, PPUU, PPUu Using a Punnett square for the cross, we will get the following F1 and F2 offspring phenotypes and their respective ratios: F1 offspring: BU (blue-eyed, utterer) F2 offspring ratios: - 9/16 blue-eyed, utterer - 3/16 green-eyed, utterer - 3/16 blue-eyed, mutterer - 1/16 purple-eyed, utterer