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.
A person has to perform crosses for the purpose of studying inheritance of a few traits/characters. What should be the criteria for selecting the organisms?
The criteria for selecting the organism to study inheritance are
(i) Easily visible and different traits
(ii) Short life span
(iii) Simple pollination procedure
(iv) Organisms must be true breeds
(v) Mating of gametes has to be random
(vi) Can be easily manipulated
The pedigree chart given below shows a particular trait which is absent in parents but present in the next generation irrespective of sexes. Draw your conclusion on the basis of the pedigree.
The pedigree chart shows that the trait is autosome linked and recessive in nature. But, the parents are carriers (i.e., heterozygous) hence, among the offsprings only few show the trait irrespective of sex. The other offsprings are either normal or carrier.
In order to obtain the $F_1$-generation Mendel pollinated a pure-breeding tall plant with a pure-breeding dwarf plant. But for getting the $\mathrm{F}_2$-generation, he simply self-pollinated the tall $\mathrm{F}_1$ plants. Why?
Characters segregate during gamete formation. Pure-breeding parents give rise to $F_1$ with heterozygous conditions. Only self-pollination of heterozygotes can result in all possible recombinations of characters in progeny as mating is random.
'Genes contain the information that is required to express a particular trait.' Explain.
Genes contain the information required to express a particular trait can be explained by the following experiment.
G Beadle and E Tatum set an experiment to prove that one gene possess a particular trait and is responsible for the production of one enzyme or protein. They performed their experiment on Neurospora crassa which were nutritionally mutant.
It was proved that a single protein contains several polypeptide and each polypeptide is controlled by separate gene. Thus, each gene expresses a particular trait. This theory was called one-gane-one enzyme or one gene-one polypeptide hypothesis.
But after the discovery of cistron (the functional unit of gene), the theory was named as one-cistron-one polypeptide hypothesis.