question_answer

(i)  In monohybrid cross of red and white flower, Mendel got only red flower. On setting the \[{{F}_{1}}\]plants having red flower he got both plants with red and white flower. Explain the basis of using RR and rr symbols to represent the genotype of plants of parental generation

(ii) A, B, D are three independently assorting genes with their recessive alleles a, b, d, respectively. A cross was made between individuals of AabbDD genotype with aabbdd. Explain the type of genotypes of the offspring produced

(iii) A progeny of \[{{F}_{1}}\] is crossed with the homozygous recessive parent. What is this cross called? Work out how is it useful?

 

Answer:

(i)  On crossing red and white flower only red colour flower appeared in the \[{{F}_{1}}\] generation. But the white colour flower again appear in the \[{{F}_{2}}\] generation which is raised out of the \[{{F}_{1}}\] individuals only. Mendel found that there is factor of each and every character. Accordingly, there has to be one factor (R) for red flower and other one factor (r) for white flower. In case, an organism possess only one copy of the gene then the possibility of reappearance of white flower in the K generation of the given cross is not there. Also the ratio (3:1 or red and white) indicates that each organism must possess two copies of a particular gene.

(ii) The given cross is Aa bb DDX aa bb dd

Accordingly the type of offspring produced would be

(iii) When a progeny of \[{{F}_{1}}\] is crossed with the homozygous recessive parent, it is called test cross. Such a cross is useful to determine the genotype of an unknown i.e. whether it is heterozygous, or homozygous dominant for the trait.