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Practice each question, then open the answer or worked solution.
What is the cross between the progeny of F1 and the homozygous recessive parent
called? How is it useful?
Ans: The cross between the progeny of F1 and the homozygous recessive parent is called test cross. The progenies of a test cross are studied to determine the phenotype in F1 generation.
Do you think Mendel’s laws of inheritance would have been different if the characters that he chose were located on the same chromosome.
Ans: If the characters were located on some chromosome, then results would have been different. It was seen by Morgan’s experiments on Drosophilla. He observed that phenotype in the F1 generation was in a different ratio than something which was observed by Mendel previously because the characters were located on the same chromosome.
Enlist the steps of controlled cross pollination. Would emasculation be needed in a cucurbit plant? Give reasons for your answer.
Ans: The steps of controlled cross pollination are:
Emasculation → Transfer of pollen from a different flower → Pollination → Fertilisation
Plants of cucurbitaceae have unisexual flowers, so cross pollination is the norm and emasculation is not needed. But in case of a monoecious plant, emasculation would be necessary.
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?
Ans: For such type to studies, the organism should meet following criteria:
They must possess easily identifiable sets of contrasting characters.
Life cycle of the organism should be short so that their study can be conveniently completed within a couple of years.
Hybridization should be easy to induce in the organism.
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.
Ans: The first row shows mating between parents. The next row shows the number of progenies. There are three male and 2 female children. One boy and one girl are affected with some genetic disorder. Thus, the trait is autosomal linked and recessive in nature.
In order to obtain the F1 generation Mendel pollinated a pure-breeding tall plant with a pure breeding dwarf plant. But for getting the F2 generation, he simply self-pollinated the tall F1 plants. Why?
Ans: When plants of F1 generation plants were produced, all of them were tall. Then Mendel wanted to understand fate of recessive characters. He did not want any other character set to mask the effect of inheritance to the F2 generation so , he self pollinated tall F1 plants
“Genes contain the information that is required to express a particular trait.” Explain.
Ans: During Mendel’s period, genes were not known but after the discovery of chromosomes, scientists discovered that genes are present on chromosomes and they were responsible for inheritance of characters. Hence, it is understood that genes contain all the information required to express a particular trait.
How are alleles of particular gene differ from each other? Explain its significance.
Ans: Genes which code for a pair of contrasting characters are alleles which are slightly different from each other in the form of absence or presence of an extra molecule of a particular substance. Alleles are significant in the sense that a particular trait can be dominant or recessive. In some instances, co-dominance can also be observed.
In a monohybrid cross of plants with red and white flowered plants, Mendel got only red flowered plants. On self-pollinating these F1 plants got both red and white flowered plants in 3:1 ratio. Explain the basis of using RR and rr symbols to represent the genotype of plants of parental generation.
Ans: Symbols RR and rr are used for the sake of convenience and using a particular alphabet has no scientific basis. Usually, the first letter of a particular trait is used to describe that character and the contrasting character is shown by the same letter but in a different case.
As per convention, dominant trait is shown by capital letter and recessive trait is shown by lower case letter.
For the expression of traits genes provide only the potentiality and the environment provides the opportunity. Comment on the veracity of the statement.
Ans: Genes are the carriers of inheritable traits and hence it can be said that the genes provide the potentiality for the expression of a particular trait. Expression of a particular trait is termed as phenotype and it is dependent on many factors. A particular trait may become recessive if it gets combined with a dominant trait. Moreover, survival of a particular trait also depends on the fact whether the trait passes the natural selection. Hence, it can be said that the environment provides the opportunity for expression of a particular trait.