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.

Heredity is the biological transmission of characteristics from parents to their offspring through genetic material. For example, certain features may be inherited because offspring receive genes from both parents. Therefore option A is correct. Digestion breaks food into simpler substances, respiration releases energy from food, and excretion removes metabolic wastes; none of these processes means the transfer of traits between generations.

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.

A dihybrid cross follows two pairs of contrasting traits at the same time. Mendel’s principle of independent assortment states that, during gamete formation, the allele pair for one trait is distributed independently of the allele pair for another trait, when the relevant conditions apply. This produces combinations not seen in the original parents. Therefore option A is correct; blending, acquired-trait inheritance and chromosome destruction do not explain the result.

Natural selection can influence evolution only when a beneficial difference is heritable. A trait may help one individual survive, but if it is not transmitted to offspring, it will not become more common through reproduction. Evolutionary change requires inherited variation to persist and alter the composition of a population over generations. Option A is correct. Survival is relevant, but without inheritance its advantage generally ends with that individual rather than spreading through the lineage.

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.

When offspring display combinations of traits that were not present together in the parents, the hereditary factors for the two traits are not being transmitted as one inseparable package. During gamete formation, allele pairs for different traits can assort independently and then recombine during fertilisation. This is Mendel’s law of independent assortment, so option A is correct. The other choices concern unrelated or scientifically unsupported ideas.

For a useful variation to become common, it generally must be heritable so that it can pass to offspring, and it must improve survival or reproductive success under the relevant conditions. Natural selection can then increase its frequency over generations, although chance and population structure also matter. Option A gives the essential requirements. B ignores inheritance and selection, C is false because variations may be beneficial, neutral or harmful, and D contradicts heredity.

Evolution is a population-level change that becomes visible across generations. A useful characteristic can help one individual survive, but it can influence the future of a population only if the genetic basis of that characteristic is transmitted to offspring. Without inheritance, the change usually ends with the individual and cannot accumulate through reproduction. Thus option A is correct. B is false because usefulness does not guarantee inheritance, while C and D contradict basic evolutionary biology.

Heredity transmits genetic information from parents to offspring, allowing particular variations to persist in a population. When heritable variations affect survival or reproduction, natural selection can change their frequency over many generations. This population-level, long-term change is evolution. Therefore option A correctly connects heredity with evolution. Acquired traits are not automatically inherited, heredity does not always prevent change, and evolution is not completed within the lifetime of one organism.

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.

The governing concept is inheritance through germ cells. Reproductive cells, such as sperm and ova, contribute genetic material to offspring during sexual reproduction. Therefore, a gene present in such a cell has a route to enter the next generation and influence an inherited trait. It is not restricted to digestion, destined to become a fossil, or unable to pass on. Hence option A correctly states its importance.

A dihybrid cross follows two pairs of contrasting traits at the same time. During gamete formation, the allele pair for one trait can separate independently of the allele pair for the other, producing parental and non-parental combinations. This observation supports Mendel’s law of independent assortment. It does not support acquired inheritance, chromosome destruction, or permanent blending of traits.

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.