Question

The snapdragon flower in Tennessee and Alabama are both white. When these two strains of snapdragon were crossed, the resulting F₁ produces purple-color flower. When the F1 was self-crossed, the F2 progeny were 540 purple and 420 white.

16. What kind of inheritance pattern is this?

A. recessive epistasis

B. complete dominance

C. dominant epistasis

D. codominance

E. complementation

17. What is the genotype of the F1 progeny? (let’s assume two involved genes are BB and DD)

A. BBdd

B. bbDD

C. BbDd

D. BBDD

E. Bbdd

18. To calculate the frequency of this inheritance pattern, we used the following branching-diagram method. Fill out the empty parenthesis. In the parentheses of phenotype section, which one is Purple phenotype?

                                                      Frequency      Phenotypes

                              3/4 D_             ( I   ) B_D_        (       A         )

      3/4 B_

                              1/4 dd            ( II ) B_dd       (       B         )

                              3/4 D_             ( III ) bb_D_    (       C         )                           

     1/4 bb

                              1/4 dd            ( IV ) bbdd       (       D        )

19. In the above diagram, the combined frequency of which categories will give you 7/16 frequency of the Colorless phenotype

A. I, II, III

B. II, III, IV

C. I, II, IV

D. I, III, IV

E. none of the above

                                                                                   

20. If you select randomly and cross again two white flowers among the F2 progeny, what is the probability of producing only purple flowers at F3 (just like two parental strains producing all purple at F1)?

A. 1/3

B. 1/7

C. 3/7

D. 9/49

E. 1/49

Answer 1

The answer to the given question has been solved below :

16. Option E : complementation; If the parental generation involved a cross between the genotype BBdd and bbDD (both colorless), resulting F1 offspring would be BbDd (purple). We assume, both dominant B and D allele are required for flower colour purple.

17. Option C : BbDd

18. Option A : B_D_ gives the 9/16 proportion of purple colour flower phenotype.

19. Option B : II, III and IV together (7/16) give the colourless phenotype.

20. Option E : 1/49. Probability of picking B_dd is 3/7 and the gamete being Bd is 1/3. Again, probability of picking bbD_ is 3/7 and the gamete being bD is 1/3. Therefore, probability of getting purple flower is 3/7×3/7×1/3×1/3=1/49.