Question

You decide to conduct a genetic analysis of these mutant lines by crossing each with a pure-breeding wild-type line. The numbers in the F2 indicate the number of progeny in each phenotypic class. Three crosses between pure lines. Cross 1 between plants with twisted and wild-type leaves results in plants with twisted leaves. An F1 F1 cross results in 53 plants with twisted leaves and 18 wild-type plants. Cross 2 between plants with forked and wild-type leaves results in plants with forked leaves. An F1 F1 cross results in 49 forked and 16 wild-type plants. Cross 3 between plants with pale and wild-type leaves results in plants with leaves of intermediate color. An F1 F1 cross results in 34 plants with intermediate leaves, 17 wild-type plants, and 16 plants with pale leaves. From these results, determine the relationship between the mutant allele and its corresponding wild-type allele in each line. Label each mutant line with the best statement from the list below. Labels may be used once, more than once, or not at all

Answer 1

Complete question:

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Answer:

• For the twist trait: The mutant allele is dominant to its corresponding wild-type allele
• For the forked trait: the mutant allele is dominant to its corresponding wild-type allele
• For the pale trait: The mutant allele is neither dominant nor completely recessive to its corresponding wild-type allele

Explanation:

• Cross 1:  twisted x wild-type ----> Pure lines

Parentals)    TT   x      tt

F1) twisted leaves, Tt. ---> Heterozygous

Parentals) Tt    x    Tt

Punnett square)    T     t

                       T    TT   Tt

                        t    Tt    tt

F2) 53 twisted, 18 wild-type

Total number of individuals in the F2 = 53 + 18 = 71

71 plants -------- 100% of the F2

53 twisted------X = 75% TT + Tt

18 wild-type----X = 25% tt

Phenotypic ratio 3:1

The phenotype of the F1 and F2 progeny tells us that the twist trait is dominant over the wild type. The fact that the whole F1 generation was twisted is enough information to assume that the wild type is recessive and the twisted is dominant. Also, the phenotypic ratio of the F2 corroborates this assumption.

• Cross 2: forked x wild-type ---> Pure Lines

Parentals)  FF     x     ff

F1) 100% forked, Ff----> Heterozygous

Parentals)  Ff     x     Ff

Punnett square)    F      f

                    F       FF    Ff

                    f        Ff     ff

F2) 49 forked and 16 wild-type plants

Total number of individuals in the F2 = 49 + 16 = 65

65 plants -------- 100% of the F2

49 forked------X = 75% FF + Ff

16 wild-type----X = 25% ff

Phenotypic ratio 3:1

The phenotype of the F1 and F2 progeny tells us that the twist trait is dominant over the wild type. The fact that the whole F1 generation was forked is enough information to assume that the wild type is recessive and the forked is dominant. Also, the phenotypic ratio of the F2 corroborates this assumption.

• Cross 3: pale x wild-type ---> Pure lines

Parentals) PP    x    pp

F1) 100% Pp, intermediate color.

Parentals) Pp   x   Pp

Punnett square)   P       p

                      P    PP    Pp

                       p    Pp    pp

F2) 34 intermediate, 17 wild-types, and 16 pale.

Total number of individuals in the F2 = 34 + 17  + 16 = 67

67 plants -------------- 100% of the F2

34 intermediate ------X = 51% Pp

17 wild-type-------------X = 25% pp

16 pale -------------------X = 24% PP

Phenotypic ratio 1:2:1

The phenotype of the F1 and F2 progeny tells us that the pale trait is not dominant neither recessive to the wild type. The fact that the whole F1 generation was intermediate is enough information to assume that none of the traits dominates over the other. This is a case of incomplete dominance.  The heterozygous individual express an intermediate phenotype between both the parentals´ one. Also, the phenotypic ratio of the F2 corroborates this assumption.  

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