Question

7. Consider the following crosses in Drosophila. The two traits being investigated involve eye color and the presence or absence of wing crossveins. The outcomes of four crosses are shown below. Number of offspring of each phenotype Parents of cross orange, crossveins red. crossveins red crossveinless orange. crossveinless orange. crossveins orange, crossveins 83 26 red, crossveins red. crossveinless 63 20 18 65 red. crossveinless 71 81 0 0 red, crossveins red crossvens red. crossveins 34 93 28 11 Which eye color is dominant and which is recessive? (a) (b) Which wing vein type is dominant and which is recessive? What is the most likely genotype of each parent for cach of the four crosses? (c) 8. In peas, axillary flowers (A) is dominant to terminal flowers (a) and colored flowers (R) is dominant to white (r). A true-breeding plant with white, terminal flowers is crossed with a true-breeding plant having colored, axillary flowers. The Fi plants are then allowed to self-pollinate. (a) Using a punnet square to illustrate, determine all possible Fa phenotypes and calculate the probability of each. (b) The F2 generation consisted of 308 plants with axillary, colored flowers; 34 plants with terminal, white flowers; 118 plants with axillary, white flowers; and 132 plants with terminal, colored flowers. Using the chi-square test, determine if this outcome is consistent with the predicted ratios for this cross.

Answer 1

7.a) Red eye colour is dominant and orange eye color is recessive. Explanation- From cross 4, it can be observed that the result resembles the dihybrid cross ratio i.e. 9 (red crossveins) : 3 (red crossveinless) : 3 (orange crossveins) : 1 (orange crossveinless).

b) Crossvein wing type is dominant and crossveinless wing type is recessive. Explanation- From cross 4, it can be observed that the result resembles the dihybrid cross ratio i.e. 9 ( red crossveins) : 3 ( red crossveinless) : 3 ( orange crossveins) : 1 (orange crossveinless).

c) If we denote red allele as 'R', orange allele as 'r' and crossvein allele as 'C', crossveinless allele as 'c', then the parental genotypes are as follows.:

Cross 1- rrCc, rrCc

Cross 2- RrCc, Rrcc

Cross 3- RRcc, RRCc

Cross 4- RrCc, RrCc

8.

A.
Parent hauete reaa X rea RRAA (RA) Rre Aa F XF Caneles Rretta Ralaltica X Rr Aa A Roccabra (RA) RRAA RR Aa RL AA hr Aa Colour, Anillany colon, pillary Colonn, Brillary Colour, Arillary RR Aa RRaa Ruta Ruda Colaug Arillary Colow, Ferminal Colom, Anillarn Colow, Terminal EA ROAA Rnta in AA reneta Colon, Anillary Coloen, Hillary allite Anillam ullute, Anillary Cro Rh Aa Rraa ren Aareraa colour pillary Colon, Terminal White Anillary White, Terninal Probability of Colored, Arillary flowen = 9/16 o colored, Teruemal flowers = 3116 White , Anillarry flowen = 3/16 White, Terenimal flower - 1/16.
B.
d ď b) Enfected obserwed Expected Dermation Ratio Value (0) Value (E) (d=0-E) 916 308 333 -25 3/ 118 11 +7 3/26 132 11 tu 1/16 34 37 -3 Total -592 625 1.876 49 0.441 441 3.972 9 0.243 x² = 6.532 - Degnee of freedom = n-1 = 9-1=3 Probaleétity of n = 6.532 at d. o.f 3 = 0.10 As the probability value is more than creetical value cooos), this controme is consisfent with predicted reatio.