Question

You are studying leaf development in a member of the mustard family. You identify several mutants of interest in this plant and make pure (true-breeding) lines of each mutant for further study. You decide to conduct a genetic analysis of these mutant lines by crossing each with a pure wild-type line. The numbers in the F2 indicate the number of progeny in each phenotypic class. Three crosses between pure lines of flowers. The first cross is between twist and wild type flowers. F1 flowers have twisted leaves. When F1 flowers were crossed with each other, 53 twisted and 18 wild type flowers were obtained. The second cross is between forked and wild type flowers. The F1 generation is all forked, and when they are crossed with each other, 49 forked and 16 wild type flowers were obtained. The third cross is between pale and wild type flowers. The F1 generation was of middle coloring and when they were crossed with each other, 17 wild type, 16 pale, and 34 middle type flowers were obtained. From these results, determine the relationship between the mutant allele and its corresponding wild-type allele in each line.

Answer 1

Answer:

•The relationship between the twist and the wild type flower in the first crossing is known as a COMPLETE DOMINANCE

•The relationship between the forked and the wild type flower in the second crossing is also known as a COMPLETE DOMINANCE

•The relationship between the pale and the wild type flower in the third crossing is known as an INCOMPLETE DOMINANCE

Explanation:

A complete dominance is characterised by having one of the genes (the dominant gene) in an heterozygous condition, completely masking the effect of the other (the recessive gene) of thesame allelic pair. E.g. if the genes in allelic is represented with Aa, "A" is said to completely dominate "a" if it does not allow "a" to Express itself phenotypically.

The heterozygous condition is always the result of the F1 generation

and the F2 generation of a Complete dominance is always characterised by a phenotypic ratio of 3:1 which is in line with the results gotten from the first crossing and the second crossing as stated in the question.

An complete dominance is characterised by having an intermediate progeny in the F1 generation which was evident in the result of the third crossing. Also a phenotypic ratio of 1:2:1 in the F2 generation is also a characteristic feature of an Incomplete dominance relationship which was also evident in the third crossing.