50. In Mendel’s experiments, when he crossed a tall (TT) pea plant with a short (tt) pea plant, what did he observe in the first generation (F1)?
[RRB Group D, 28 November 2025 (Shift 3)]
(a) Half were tall and half were short.
(b) All were tall.
(c) All were of medium height.
(d) All were short.
Answer: (b) All were tall.
Explanation: Every F1 offspring has genotype Tt, receiving T from the tall parent and t from the dwarf parent. Because tallness is dominant in Mendel’s chosen pea lines, all F1 plants appear tall even though they carry the recessive allele.
49. The observable expression of the genotype is known as __________.
[DSSSB TGT (Natural Science), 6 September 2025 (Shift 1)]
(a) Genotype
(b) Genome
(c) Gene
(d) Phenotype
Answer: (d) Phenotype
Explanation: Phenotype refers to measurable or observable features of an organism, such as flower colour or body height. It arises through interaction between genetic makeup and environment. Genotype denotes inherited alleles, whereas a genome comprises the organism’s overall genetic material.
48. The process by which traits are passed from parents to offspring is known as __________.
[RRB NTPC (Undergraduate) CBT-I, 28 August 2025 (Shift 3)]
(a) Mutation
(b) Heredity
(c) Hybridisation
(d) Linkage
Answer: (b) Heredity
Explanation: Heredity is the transmission of characteristics between generations through inherited genetic material. A mutation changes genetic information; hybridisation involves crossing different types; and linkage describes genes tending to travel together. Only heredity names the general parent-to-offspring transfer of traits.
47. What is the study of heredity and variation called?
[RRB NTPC (Undergraduate) CBT-I, 18 August 2025 (Shift 3)]
(a) Evolution
(b) Mutation
(c) Genetics
(d) Biology
Answer: (c) Genetics
Explanation: Genetics investigates genes, the transmission of traits, and differences among individuals. It includes inheritance patterns and molecular mechanisms. Biology is the broader study of life; mutation refers to alteration of genetic material, and evolution concerns population changes over generations.
46. A single gene can often have multiple effects on the phenotype of an organism, affecting a number of apparently unrelated traits. This phenomenon is known as:
[MH SET (Life Sciences), 2025]
(a) Epistasis
(b) Polygenic inheritance
(c) Pleiotropy
(d) Epigenetic effect
Answer: (c) Pleiotropy
Explanation: Pleiotropy occurs when one gene influences several distinct traits. Sickle-cell disease is a familiar example, affecting red cells and multiple organs. It contrasts with polygenic inheritance, in which many genes contribute to one characteristic, and epistasis, involving interactions between genes.
45. Which structure within the nucleus contains genetic information in the form of DNA?
[SSC MTS, 11 November 2024 (Shift 1)]
(a) Ribosome
(b) Chromosome
(c) Nucleolus
(d) Vacuole
Answer: (b) Chromosome
Explanation: Chromosomes consist principally of DNA packaged with proteins and contain many genes. In eukaryotic cells, they occupy the nucleus and become particularly conspicuous during cell division. Ribosomes synthesize proteins, while nucleoli participate in ribosome production rather than serving as chromosomes.
44. Which specific chemical can be applied to achieve staining of chromosomes?
[SSC MTS, 23 October 2024 (Shift 1)]
(a) Ethanol
(b) Hydrochloric acid
(c) Acetocarmine
(d) Methanol
Answer: (c) Acetocarmine
Explanation: Acetocarmine stains chromosomal material and helps make dividing-cell chromosomes visible under a microscope. It is commonly used in plant cytology and chromosome preparations. The alternative chemicals listed are not the standard chromosomal stain required by this question.
43. Select the INCORRECT statement.
[SSC MTS, 9 October 2024 (Shift 3)]
(a) Functional segments of DNA are called genes.
(b) Chromatin forms rod-shaped chromosomes when a cell approaches division.
(c) Chromosomes are composed of DNA and carbohydrates.
(d) DNA carries information needed to build and organise cells.
Answer: (c) Chromosomes are composed of DNA and carbohydrates.
Explanation: Eukaryotic chromosomes consist of DNA associated primarily with proteins, especially histones, not carbohydrates as a principal structural component. Genes are functional DNA sequences, and chromatin condenses into visible chromosomes for cell division. Accordingly, the third statement is incorrect.
42. Which of the given options is rod-shaped, carries genetic information, is visible especially during cell division and is present in the nucleus?
[SSC MTS, 8 October 2024 (Shift 2)]
(a) Chromosomes
(b) Lysosomes
(c) Ribosomes
(d) Cytoplasm
Answer: (a) Chromosomes
Explanation: During mitosis, chromatin condenses into distinct chromosomes that can appear rod-shaped under a microscope. Chromosomes carry genes and ensure orderly distribution of DNA to daughter cells. Lysosomes digest cellular material, ribosomes translate RNA, and cytoplasm is the surrounding cellular region.
41. Which of Mendel’s laws states that a diploid organism passes one allele for a trait to its offspring, so the offspring receive one allele from each parent?
[SSC CHSL Tier-I, 5 July 2024 (Shift 2)]
(a) Law of independent assortment
(b) Law of paired factor
(c) Law of dominance
(d) Law of segregation
Answer: (d) Law of segregation
Explanation: The law of segregation states that the two alleles at a gene locus separate during gamete formation. Each gamete normally receives one allele, and fertilisation combines parental contributions. This explains the characteristic 3:1 phenotypic ratio of a standard monohybrid F2 cross.
