In the $F_2$-generation of a Mendelian dihybrid cross the number of phenotypes and genotypes are
phenotypes-4, genotypes-16
phenotypes-9, genotypes-4
phenotypes-4, genotypes-8
phenotypes-4, genotypes-9
Mother and father of a person with ' 0 ' blood group have ' $A$ ' and ' $B$ ' blood group respectively. What would be the genotype of both mother and father?
Mother is homozygous for ' A ' blood group and father is heterozygous for ' B '
Mother is heterozygous for ' A ' blood group and father is homozygous for ' B '
Both mother and father are heterozygous for ' A ' and ' B ' blood group respectively
Both mother and father are homozygous for ' A ' and ' B ' blood group respectively
What is the cross between the progeny of $F_1$ and the homozygous recessive parent called? How is it useful?
When a progeny of $F_1$ is crossed with the homozygous recessive parent, it is called test cross.
Test cross between pure dominant $(\mathrm{A})$ and hybrid dominant $(\mathrm{B})$ individuals with recessive parent is shown below
Such a cross is useful to determine the genotype of an unknown trait, i.e., whether it is heterozygous or homozygous dominant for the trait.
Do you think Mendel's Laws of inheritance would have been different in the characters that he chose were located on the same chromosome.
If the characters are present on the same chromosome they would not assort independently as they are linked on the same chromosome. Percentage of linkage depends on the distance between the genes. With linkage no conclusive laws can be drown.
Enlist the steps of controlled cross-pollination. Would emasculation be needed in a cucurbit plant? Give reasons for your answer.
Steps of controlled cross-pollination are
(i) Selection of parents with desired characters.
(ii) Emasculation, i.e., if the female parent bears bisexual flowers, before dehiscence anther should be removed by forceps.
(iii) Bagging, i.e., emasculated flowers have to be covered with a bag of suitable size, generally made up of butter paper, to prevent contamination of its stigma with unwanted pollen.
(iv) When the stigma of bagged flower attains receptivity, mature pollen grains collected from anthers of the male parent are dusted on the stigma
(v) The flowers are rebagged and the fruits are allowed to develop.
Emasculation is not always needed in a cucurbit plant. Emasculation is essential only in case of bisexual flowers to prevent self-pollination. In case of cucurbit plant, female parent produces usually unisexual flowers but may sometimes have bisexual flowers.