Inheritance

The governing principle is sexual reproduction and chromosome inheritance. The mother’s ovum and the father’s sperm are haploid, so each contributes 23 chromosomes. At fertilisation, 23 + 23 = 46 chromosomes in the zygote, giving the offspring one set from each parent. Therefore option C is correct. Options A and B wrongly assign the entire set to one parent, and food does not supply chromosomes.

The governing concept is inheritance across generations. Reproductive cells carry genetic information to offspring, allowing a heritable variation to be transmitted and possibly become more or less common through selection or other evolutionary processes. A trait that exists only in body cells, such as many acquired changes, normally cannot be passed through reproduction, so it contributes little directly to evolutionary change. Therefore A is correct; dominance, fossils, and chromosome-number increase do not explain transmission.

The governing concept is the combined action of heredity and variation. Heredity transfers genetic information from parents, producing resemblance. During reproduction and genetic copying, differences can arise through recombination or small copying changes, producing variation. Therefore option B explains both similarity and difference. Food, soil, or weather alone cannot account for the inherited pattern in offspring.

Mendel needed traits that could be observed and compared clearly across generations. Pea plants offered distinct contrasting characteristics, such as tall versus dwarf stems and round versus wrinkled seeds. They also reproduce readily and can be self-pollinated or cross-pollinated. Therefore option A gives a valid main reason; the remaining choices are factually incorrect.

The reappearance of a recessive trait in the second generation supports Mendel’s view that hereditary factors, now called alleles, are transmitted as distinct units rather than permanently blending. A recessive allele may be hidden when paired with a dominant allele in F1, but it remains present and can combine with another recessive allele in F2. Gamete formation and fertilisation are essential to this pattern. Therefore option A is correct.

Muscle enlargement caused by continuous exercise is an acquired modification of the wrestler’s body. It may change muscle size and strength in his somatic cells, but it does not normally change the genes in his sperm-producing cells. Inheritance transfers genetic information through reproductive cells, not the effects of ordinary training. Thus option A is correct. Muscles can grow, children inherit traits from both parents, and exercise does not destroy chromosomes.

DNA is the molecule that stores biological information. Specific sections of DNA are called genes, and genes contain instructions that help determine proteins and inherited characteristics. During reproduction, DNA is copied and transmitted through reproductive cells, allowing offspring to receive genetic information from their parents. Thus option A is correct. DNA has many functions beyond any single trait, while producing energy and digesting food are not its defining roles.

In eukaryotic cells, chromosomes are thread-like structures in the nucleus, made largely of DNA and associated proteins. A gene is a functional segment of DNA, and many genes are arranged at particular locations on chromosomes. This physical organisation allows genetic information to be copied and passed to daughter cells and offspring. Therefore option A is correct. Chromosomes and genes are closely related, and both plants and animals possess them.

Cutting a mouse’s tail changes its body but does not normally change the hereditary information in its sperm or eggs. If tailless parents continue to produce offspring with tails, the observation refutes the idea that every bodily alteration becomes an inherited trait. It supports the distinction between acquired changes and heritable genetic variation. Therefore option A states the misconception being rejected; B, C, and D are compatible with genetics.

The governing concept is the difference between acquired and inherited variation. A colour change caused by sunlight affects the organism during its lifetime, but it does not normally alter the DNA of its gametes. Since gametes carry hereditary information to offspring, the change is not transmitted and cannot accumulate through generations. Therefore option A is correct; sunlight does not erase all genes, and the change does not pass to every child.

The governing concept is heritable variation followed by natural selection. A change in a gamete can be transmitted to offspring because gametes carry genetic information. If the change improves survival or reproduction, individuals possessing it may leave more offspring, causing the trait to become more common over generations. Hence option A is correct; the other choices deny inheritance or confuse a genetic change with fossil formation.

The governing concept is the distinction between acquired and inherited traits. Exercise can enlarge muscles during an individual’s lifetime, but this body change normally does not alter the DNA of the reproductive cells. Since evolution across generations depends on heritable genetic variation, the exercised muscles are not transmitted as a programmed trait to offspring. Thus A is correct; B, C and D confuse acquired changes with genes or fossils.

The governing distinction is between somatic changes acquired during life and hereditary information carried by reproductive cells. Exercise, scars or learned abilities may alter body cells or behaviour, but they usually do not change the genes in sperm or eggs. Without a change in reproductive-cell DNA, the trait is not transmitted genetically. Option B is correct; usefulness, fossils and dominance do not explain inheritance.

Heredity transmits genetic information and traits from parents to offspring, whereas variation creates differences among offspring. Evolution requires both: variation provides alternative traits, and heredity preserves and passes advantageous heritable traits to later generations. Natural selection can therefore change the frequency of traits in a population. Heredity alone would copy traits, and acquired traits alone do not adequately explain genetic evolution.