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Practice each question, then open the answer or worked solution.
A, B, D are three independently assorting genes with their recessive alleles a, b, d, respectively. A cross was made between individuals of Aa bb DD genotype with aa bb dd. Find out the type of genotypes of the offspring produced.
Ans: The following Punnett Square shows the genotype of F1 generation:
abd | |
AbD | AabbDd |
abD | aabbDd |
In our society, a woman is often blamed for not bearing male child. Do you think it is right? Justify.
Ans: From the concept of sex determination in humans, it is clear that Y chromosome which is present in males comes from the father and not from the mother. Hence, it is the man who should be blamed for not having a male child rather than the woman. But chances of an X or Y chromosome ending up in the zygote is equal, i.e. 50: 50. So, it is purely a chance that a girl or a boy is born and no one should be blamed or rewarded for the same.
Discuss the genetic basis of wrinkled phenotype of pea seed.
Ans: Seeds dry before they are ready for dispersal and subsequent germination. If there is enough starch in the seed, then the seed is round otherwise wrinkled seeds are produced. Relative amount of starch in the seed is controlled by a gene. A mutant gene in pea plants results in enzymes which lessen the amount of starch in seeds and thus seeds become wrinkled.
Even if a character shows multiple allelism, an individual will only have two alleles for that character. Why?
Ans: Most of the organisms are diploid and thus alleles can only be present in pairs. Hence, in spite of multiple allelism; an individual will only have two alleles for that character. Example: IA, IB and i alleles which govern the ABO blood grouping in humAns:
How does a mutagen induce mutation? Explain with example.
Ans: Mutagens are chemical and physical factors which can induce mutation. They do so by altering the base pair sequence in the DNA during replication.