Preparing for the UPSC Prelims can be an arduous task, especially when it comes to mastering the intricacies of biology, particularly genetics and evolution. In this realm, understanding the fundamental principles and the intricate nuances of genetic inheritance, mutation, natural selection, and the broader mechanisms of evolution is paramount. The UPSC Prelims Topic Wise Questions in Biology delve deep into these subjects, challenging aspirants to not only grasp theoretical concepts but also to apply them in real-world scenarios. With a blend of theoretical knowledge and practical understanding, aspirants can navigate through these questions, laying a strong foundation for success in the competitive examination.
Q1. Which of the following professional(s) are more likely to run the risk of a permanent change in their cell’s DNA? (1996)
1. Researchers using carbon-14 isotope
2. X-ray technician
3. Coal miner
4. Dyer and painter
Select the correct answer using the codes given below
(a) Only 2
(b) 1, 2 and 3
(c) 1, 2 and 4
(d) 1, 3 and 4
Ans. (b)
The Carbon-14 isotope, X-ray technicians, and coal miners are all susceptible to a potential permanent alteration in their DNA. X-rays possess the capacity to harm cells and tissues, potentially inducing mutations. Excessive exposure to X-rays can result in cellular damage and increase the risk of cancer. Researchers utilizing C-14 isotopes and coal miners, even when exposed to lower concentrations of radiation over time, face the prospect of DNA mutations.
Conversely, dyers and painters are not subject to the same risk of permanent DNA alteration. Paints and dyes typically do not contain mutagens, thus reducing the likelihood of cellular mutations in these professions.
Q2. Haemophilia is a genetic disorder which leads to
(a) decrease in haemoglobin level
(b) rheumatic heart disease
(c) decrease in WBC
(d) non-clotting of blood
Ans. (d)
Hemophilia, a genetic disorder, disrupts the blood clotting process, leading to prolonged bleeding. This condition is caused by a recessive gene on the X chromosome, meaning it manifests when the dominant gene is absent. Consequently, it primarily affects males who inherit the gene from carrier females. The disorder impacts a key protein crucial for clotting, causing even minor injuries to result in persistent bleeding in affected individuals.
Q3. Match List-I with List II and select the correct using the codes given below the lists: (1998)
List I – List II
A. Theory of mutation – 1. Beadle and Tatum
B. Theory of evolution – 2. Jacob and Monod
C. One gene one enzyme hypothesis – 3. Darwin
D. Operon concept – 4. de vries
Codes
ABCD
(a) 3 4 1 2
(b)4 3 1 2
(c) 4 3 2 1
(d) 3 4 2 1
Ans. (b)
The accurate pairing is as follows: A-4, B-3, C-1, D-2. The theory of mutation was hypothesized by Hugo de Vries in 1901. Darwin proposed the theory of evolution in the 19th century. Beadle and Tatum formulated the one gene one enzyme hypothesis following their experiments on Neurospora crassa. The concept of operon was introduced by Jacob and Monod.
Q4. Which one of the following genetic diseases is sex-linked? (1999)
(a) Royal haemophilia
(b) Tay-Sachs disease
(c) Cystic fibrosis
(d) Hypertension
Ans. (a)
Royal hemophilia, also known as the “Royal disease,” is a sex-linked condition that has been notably prevalent among European royal families. It traces its spread back to Queen Victoria’s descendants (1819-1901). This condition, characterized by impaired blood clotting, is a recessive trait linked to the X chromosome. In contrast, Tay-Sachs disease, an autosomal recessive disorder, is located on non-sex chromosomes.
Q5.
Assertion (A) In human beings, the female plays a major role in determining the sex of the offspring.
Reason (R) Women have two ‘X’-chromosomes. (2000)
Codes
(a) Both A and R are true and R is the correct explanation of A
(b) Both A and R are true, but R is not a correct explanation of A
(c) A is true, but R is false
(d) A is false, but R is true
Ans. (d)
Assertion: Exp. A is false, but R is true. The assertion can be corrected as follows: In human beings, males play the major role in determining the sex of the offspring because they carry both X and Y chromosomes, whereas females carry two X chromosomes. Therefore, it is the sperm, whether carrying an X or Y chromosome, that fuses with the egg and determines the sex of the fetus.
Q6. In the context of organic evolution, the loss of limbs in snakes is explained by the phenomenon of (2002)
(a) use and disuse of organs
(b) adaptation to living in burrows
(c) natural selection
(d) inheritance of acquired characters
Ans. (a)
In the realm of organic evolution, the absence of limbs in snakes is elucidated by the principle of organ use and disuse. Lamarck posited that in evolution, body parts utilized more frequently tend to strengthen and improve, whereas those underutilized or unused tend to diminish over time. Hence, the loss of limbs in snakes exemplifies the concept of organ use and disuse.
Q7. When one gene controls two or more different characters simultaneously, the phenomenon is called (2002)
(a) apomixis
(b) pleiotropy
(c) polyploidy
(d) polyteny
Ans. (b)
Pleiotropy occurs when a single gene governs multiple distinct traits concurrently. This phenomenon, exemplified by conditions like Tay-Sachs disease, demonstrates how one genetic element can impact various characteristics simultaneously.
Q9. Among living organisms, which one of the following is the most responsible factor for bringing about the origin of a new species? (2002)
(a) Isolation
(c) Natural selection
(b) Mutation
(d) Sexual reproduction
Ans. (a)
The primary catalyst for the emergence of new species is isolation. Speciation, the process through which new and distinct species evolve, entails the division of a single evolutionary lineage into multiple genetically independent ones. There are two principal forms of speciation:
- Allopatric speciation arises from geographical isolation, leading to the subsequent divergence of separated populations due to factors like genetic drift or natural selection.
- Sympatric speciation occurs through ecological isolation, where populations diverge within the same geographic area, often driven by rapid chromosomal changes like polyploidy.
While factors like mutation, natural selection, and sexual reproduction contribute to species variation, isolation stands out as the most crucial factor in initiating the formation of new species among the provided options.
Q10. Which of the following features of DNA makes it uniquely suited to store and transmit genetic information from generation to generation? (2002)
(a) Complementrity of the two strands
(b) Double helix
(c) Number of base-pairs per turn
(d) Sugar-phosphate backbone
Ans. (a)
The distinctive attribute of DNA, enabling it to efficiently store and pass on genetic information across generations, lies in the complementary nature of its two strands. To safeguard against degradation by cytoplasmic enzymes, DNA possesses the remarkable ability of replication, ensuring the faithful production of carbon copies. This process is vital for the seamless transfer of genetic material from parent cells to their offspring and perpetuates the transmission of information from one generation to the next.
Q11. Match List I with List II and select the correct answer using the codes given below (2002)
List I (Achievement in Genetics) List II (Scientists)
A. Discovery of transduction and conjugation in bacteria 1. Khorana
B. Establishing the sex-linked inheritance 2. Komberg
C. Isolation of DNA polymerase from Ecoli 3. Lederberg
D Establishing the complete genetic code 4. Morgan
5. Ochoa
Codes
ABCD
(a) 4 3 2 1
(b) 3 4 2 5
(c) 4 3 1 5
(d) 3 4 2 1
Ans. (d)
The accurate pairings are: A-3, B-4, C-2, D-1. Lederberg (1952) unveiled the discoveries of transduction and conjugation in bacteria, while T.H. Morgan popularized theories on sex-linked inheritance around 1808. Arthur Kornberg isolated DNA polymerase from E. coli, and Har Gobind Khorana elucidated the complete genetic code, a set of three-letter nucleotide combinations, earning him the Nobel Prize in 1968.
Q12. Among the following, which one is not an ape? (2008)
(a) Gibbon
(b) Gorilla
(c) Langur
(d) Orangutan
Ans. (c)
Among these options, langurs are not classified as apes. Grey langurs, a collective of Old World monkeys, constitute the entire genus Semnopithecus.
Q13. Nobel Prize winning scientist James D Watson is known for his work in which area? (2008)
(a) Metallurgy
(b) Meteorology
(c) Environmental protection
(d) Genetics
Ans. (d)
Renowned Nobel laureate James D. Watson made indelible contributions to the field of genetics, particularly renowned for his groundbreaking discovery of the DNA molecule, symbolized by its initials. Together with his collaborator Francis Crick, they unveiled the elegant double helix model, a revelation that echoed globally. This seminal work revolutionized the study of biology and the genetics of DNA molecules, laying the groundwork for modern biotechnology practices such as recombinant DNA techniques. In acknowledgment of their pioneering achievement, Watson and Crick were jointly awarded the 1962 Nobel Prize in Physiology and Medicine, alongside Maurice Wilkins.
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