Biology MCQs
Topic Notes: Biology
MCQs and preparation resources for competitive exams, covering important concepts, past papers, and detailed explanations.
Plato
- Biography: Ancient Greek philosopher (427–347 BCE), student of Socrates and teacher of Aristotle, founder of the Academy in Athens.
- Important Ideas:
- Theory of Forms
- Philosopher-King
- Ideal State
1
Which of the following factors is known to influence the strength of genetic linkage?
Answer:
X-rays
Genetic linkage refers to the tendency of genes located close together on the same chromosome to be inherited together. Environmental factors such as X-rays or high temperatures can induce chromosomal breaks or increase the frequency of crossing over, thereby reducing the strength of linkage between specific gene loci.
2
What characterizes an autopolyploid organism?
Answer:
Duplication of the same genome
Autopolyploidy occurs when an organism possesses more than two complete sets of chromosomes, all derived from the same ancestral species. This is distinct from allopolyploidy, which involves the combination of chromosome sets from different species through hybridization followed by genome doubling.
3
How is the strength of genetic linkage between two genes related to the physical distance between them on a chromosome?
Answer:
Inversely proportionate to the distance between them
Genetic linkage refers to the tendency of genes located close together on the same chromosome to be inherited together. As the physical distance between two genes increases, the probability of a crossover event occurring between them also increases, which reduces the strength of their linkage. Therefore, linkage strength is inversely proportional to the distance.
4
Where are linked genes located within the cellular structure of an organism?
Answer:
same chromosome
Genetic linkage occurs when genes are situated in close proximity on the same chromosome. Because they are physically connected, these genes tend to be inherited together during meiosis, violating the principle of independent assortment. The frequency of recombination between linked genes can be used to map their relative positions on the chromosome.
5
Who defined genetic linkage as the tendency of genes on the same chromosome to remain in their original combination and enter the same gamete together?
Answer:
Morgan (1910)
Thomas Hunt Morgan is credited with the discovery and definition of genetic linkage through his extensive work with Drosophila melanogaster. He observed that certain traits did not follow Mendel's law of independent assortment because the genes were physically located close together on the same chromosome, causing them to be inherited as a single unit.
6
What term describes a polyploid organism that typically arises from hybridization between parents of different ploidy levels?
Answer:
Secondary polyploid
Secondary polyploids are generally formed through the hybridization of species with different chromosome numbers or ploidy levels, often followed by chromosome doubling. This process contributes to the complexity of plant genomes and evolutionary diversification.
7
What is the term for the phenomenon where the occurrence of one crossover event reduces the likelihood of another crossover occurring in the immediate vicinity?
Answer:
Interference
Chromosomal interference is a genetic phenomenon where a crossover event in one region of a chromosome decreases the probability of a second crossover occurring nearby. This is quantified by the coefficient of coincidence, which measures the ratio of observed double crossovers to expected double crossovers.
8
Which researcher published the paper titled 'Nondisjunction as a Proof of Chromosome Theory of Heredity' in 1916?
Answer:
Bridges in 1916
Calvin Bridges, a student of Thomas Hunt Morgan, provided definitive evidence for the Chromosome Theory of Heredity. His 1916 paper on nondisjunction in Drosophila melanogaster demonstrated that the abnormal segregation of chromosomes during meiosis directly correlated with specific inheritance patterns, confirming that genes are physically located on chromosomes.
9
In genetic mapping, which relative distance between loci typically results in the highest level of crossover interference?
Answer:
Very close to each other
Crossover interference refers to the phenomenon where a crossover event in one region of a chromosome reduces the probability of a second crossover occurring nearby. This effect is most pronounced when loci are physically very close to each other on the chromosome.
10
Why are chromosomal inversions sometimes described as 'cross-over suppressors'?
Answer:
Cross-over suppressors
Inversions are called crossover suppressors because any crossover event occurring within the inverted segment during meiosis typically results in unbalanced gametes (deletions or duplications). Consequently, offspring inheriting these recombinant chromosomes are often non-viable, effectively reducing the recovery of crossover products.