University:
University of Cincinnati
Course:
BIOL 1081 | Biology I
Academic year:

2023
Views:

298

Pages:

2
Author:

Albert Huffman

BIOLOGY FREE-RESPONSE QUESTION A new species of fly was discovered on an island in the South Pacific. Several different crosses were performed, each using 100 females and 100 males. The phenotypes of the parents and the resulting offspring were recorded. Cross I: True-breeding bronze-eyed males were crossed with true-breeding red-eyed females. All the F1 offspring had bronze eyes. F1 flies were crossed, and the data for the resulting F2 flies are given in the table below. F2 Phenotype Male Female Bronze Eyes 3,720 3,800 Red Eyes 1,260 1,320 Cross II: True-breeding normal-winged males were crossed with true-breeding stunted-winged females. All the F1 offspring had stunted wings. F1 flies were crossed, and the data for the resulting F2 flies are given in the table below. F2 Phenotype Male Female Normal Wings 1,160 1,320 Stunted Wings 3,600 3,820 Cross III: True-breeding bronze-eyed, stunted-winged males were crossed with true-breeding redeyed, normalwinged females. All the F1 offspring had bronze eyes and stunted wings. The F1 flies were crossed with truebreeding red-eyed, normal-winged flies, and the results are shown in the table below. Phenotype Male Female Bronze Eyes, Stunted Wings 2,360 2,220 Bronze Eyes, Normal Wings 220 300 Red Eyes, Stunted Wings 260 220 Red Eyes, Normal Wings 2,240 2,180 a) What conclusions can be drawn from Cross I and Cross II? Explain how the data support your conclusions for each cross. In Cross I, it is apparent that there bronze eyes were dominant to the red eyes, as per Mendelian inheritance (autosomal, non-sex-linked) with an approximate ratio of 3:1 and an equal distribution between the males and females for the F2 phenotypes. In Cross II, it is apparent that the stunted wings were dominant to the normal wings, as per Mendelian inheritance (autosomal, non-sex-linked) with an approximate ratio of 3:1 and an equal distribution between the males and females for the F2 phenotypes. b) What conclusions can be drawn from the data from Cross III? Explain how the data support your conclusions. The genes for bronze eyes are linked to the genes for stunted wings and the genes for red eyes are linked to normal wings; however, the genes were far enough apart that a noticeable rate of crossover occurred because they were at least 10 gene units apart. We can deduce this because the phenotypes were not a 1:1:1:1 ratio (as they would be by independent assortment) and the parental phenotypes were present in 90 percent of the offspring, as per the Hardy Weinberg equation. c) Identify and discuss TWO different factors that would affect whether the island’s fly population is in Hardy-Weinberg equilibrium for the traits above. The population would need to be large enough for there to be no genetic drift among the flies and they would need to mate randomly, so that there would be no change in the gene pool due to mating preferences. Additionally, there would have to be no mutations so that no new alleles are introduced to the population, no emigration/immigration from the area to keep the gene pool from changing due to the addition or loss of alleles, and natural selection could not be occuring so that no alleles are favored or disfavored by the environment.