Heredity and Evolution

Biological classification groups organisms according to shared characteristics and reveals patterns of similarity and difference. Organisms with more fundamental similarities may share a more recent common ancestor, while major differences can indicate greater evolutionary separation. Classification alone is not the only evidence; fossils, comparative anatomy, embryology and molecular data also strengthen conclusions. Thus option A is correct, while the other choices describe unrelated or impossible effects.

In evolutionary biology, shared structural, developmental or molecular features can indicate common ancestry. When two organisms show more significant similarities, they may have diverged from a relatively recent common ancestor and therefore have a closer evolutionary relationship. However, one superficial feature is not enough; several lines of evidence should be compared. Option A is correct. The other options wrongly deny relationships, equate species, or deny the presence of genes.

External appearance can be misleading because unrelated organisms may face similar environmental demands and evolve similar shapes or functions. These are analogous similarities and do not necessarily indicate close ancestry. For example, wings of birds and insects both support flight but have different structural plans. Evolutionary relationships should therefore be assessed with internal anatomy, fossils, embryology and molecular evidence as well. Option A is correct; the other choices make absolute or false claims.

Darwin used the idea of struggle for existence to explain competition among organisms for limited food, space, shelter, and mates. Individuals in the same population vary, and some variations provide an advantage in a particular environment. Such organisms are more likely to survive and reproduce, passing those useful inherited traits to offspring. Therefore, option A is correct; the other choices incorrectly describe struggle as total death or as unrelated to biology.

Adaptation refers to a heritable feature that improves an organism’s chances of surviving or reproducing in a particular environment. Natural selection acts on existing variation: organisms with advantageous inherited traits tend to leave more offspring, so those traits may become more common in the population over generations. Thus option A correctly states the relationship. Adaptation is not produced instantly, and selection does not destroy every trait.

If green colour provides camouflage, birds may detect green insects less easily. The insects that survive more often have a greater opportunity to reproduce, and the trait may be passed to their offspring if it is inherited. Across many generations, the proportion of green insects can therefore increase in the population. Option A is correct; natural selection is gradual, does not instantly change every insect, and does not cause birds to lose chromosomes.

Natural selection changes the composition of a population across generations, not merely the condition of one individual. A variation that improves survival or reproduction can influence evolution only when it is transmitted to offspring. If the variation is not inherited, it disappears when the individual dies and cannot become more frequent in the population. Therefore option A is correct; digestion and chromosome destruction are unrelated to this requirement.

A plant with one dominant allele and one recessive allele is heterozygous and usually appears tall because the dominant allele masks the recessive one. It can nevertheless pass the recessive allele to a gamete. If an offspring receives one recessive allele from each parent, its genotype is homozygous recessive, so the dwarf phenotype is expressed. Thus option A is correct; receiving no gene is impossible and a dominant allele masks dwarfness.

Evolution is a change in the inherited characteristics of a population over successive generations. An individual may change during its lifetime because of growth, learning, exercise, or environmental effects, but such acquired changes generally do not alter the population’s hereditary makeup. Evolution requires heritable variation, reproduction, and changes in trait frequencies over time. Therefore option A is correct; the other choices confuse individual development with population evolution.

Fossils are preserved remains or traces that provide a record of organisms living in the past and can show changes through geological time. Homologous organs have the same basic structural plan in different organisms, even when their functions differ, suggesting inheritance from a common ancestor followed by modification. Together, these forms of evidence support evolutionary relationships. Thus option A is correct; the other choices are unrelated to fossils or comparative anatomy.

Inheritance allows a variation to pass from parents to offspring. If a small change improves survival or reproductive success, natural selection may make it more common in later generations. Other variations can accumulate with it, and the combined shift in trait frequencies can gradually produce a major difference in the population. Therefore option A is correct. The distractors contradict inheritance or incorrectly treat evolutionary change as immediate or unrelated to populations.

Natural selection is context-dependent: a trait that is advantageous in one environment may provide little benefit or even become disadvantageous when conditions change. For example, a change in climate, food availability, or predators can alter which variations improve survival and reproduction. Consequently, the direction of selection may shift toward different traits. Option A is correct; identical organisms provide no variation for selection, and without reproduction or chromosomes the proposed process cannot operate normally.

Heredity explains how genetic information and traits pass from parents to offspring, while evolution describes changes in inherited characteristics in populations over many generations. Heritable variation is essential because natural selection, genetic drift, and other processes can act on it. Thus, the two topics are scientifically connected. Option A is correct; the other choices deny their biological relationship or confuse them with unrelated processes.

A scar is an acquired characteristic produced by injury during an individual’s lifetime. It generally affects somatic, or body, cells and does not alter the DNA of the germ cells that form eggs or sperm. Since hereditary information is transmitted through germ cells, the scar is not normally inherited by offspring. Therefore option A is correct; dominance, absence of chromosomes, and fossilisation are unrelated explanations.

Natural selection changes the frequency of heritable variations when environmental conditions give some individuals a survival or reproductive advantage. Individuals with a beneficial inherited trait are more likely to survive, reproduce, and pass its alleles to their offspring. Over generations, the trait can therefore become more common in the population. A weakness, a non-heritable scar, or a trait not transmitted through reproductive cells will not explain this process. Option A is correct.

In the usual human chromosomal pattern, a mother has XX sex chromosomes and her egg contributes an X chromosome. A father has XY chromosomes and his sperm may carry either X or Y. Fertilisation by an X-bearing sperm produces XX, while fertilisation by a Y-bearing sperm produces XY. Thus the sex chromosome contributed by the father determines the chromosomal combination. This does not mean that either parent is responsible in a moral sense; it describes random biological inheritance. Option A is correct.

A family tree, also called a pedigree, records the occurrence of a characteristic among members of successive generations. By comparing parents, children, and other relatives, it helps researchers trace whether a trait tends to be transmitted and infer possible inheritance patterns. Therefore option A is correct. Fossil fuel, the water cycle, and digestion concern energy resources, environmental processes, and nutrition respectively, not the transmission of a family trait.

The governing concept is dominance and recessiveness in a monohybrid cross. If the parental plants are pure yellow YY and green yy, all first-generation plants are Yy and appear yellow because Y is dominant. Crossing Yy × Yy gives YY, Yy, Yy and yy; the yy combination expresses green seeds in the second generation. Thus the recessive trait is hidden in F1 but can reappear in F2.

The governing concept is Mendel’s law of segregation. In a monohybrid cross such as Yy × Yy, the alleles separate during gamete formation, and the offspring genotypes occur as 1 YY : 2 Yy : 1 yy. Because YY and Yy show the dominant phenotype while yy shows the recessive phenotype, the observable F2 ratio becomes 3 dominant : 1 recessive. The ratio therefore reflects separation and recombination of alleles.

The governing concept is natural selection. Individuals in a population show heritable differences, and some of these variations may provide better survival or reproductive success in a particular environment. Natural selection favours such advantageous variants, allowing their associated traits to become more common over generations. Variation is not always harmful, and it does not stop reproduction or remove chromosomes. Without differences among individuals, selection would have little material on which to act.

The governing concept is natural selection acting on an advantageous adaptation. Bark-like colour provides camouflage, making the insect less visible to predators. If it survives more often, it has a greater chance to reproduce and pass any heritable basis of that colour to its offspring. Over generations, the trait may become more frequent in the population. Excretion, digestion and transpiration are physiological processes and do not explain this survival advantage.

The governing concept is that the value of an adaptation depends on environmental conditions. White fur can camouflage an animal against snow, reducing detection by predators and improving survival. In a green forest, the same white colour may make the animal more visible, so its advantage can disappear or become a disadvantage. Thus usefulness is relative to the environment; environments are not identical, and traits can influence survival and reproduction.

The governing concept is divergent evolution. Homologous organs have the same basic structural plan because they were inherited from a common ancestral pattern, although their functions may have become different in different organisms. For example, the forelimbs of humans, bats and whales contain corresponding bones but serve different purposes. Similar function is not required, and these organs are not restricted to insects or without genetic material. Therefore option A is correct.

The governing concept is homology and common ancestry. The human arm is mainly adapted for grasping and handling objects, whereas the bat wing is adapted for flight. Despite this functional difference, both contain a corresponding arrangement of bones such as the upper arm, forearm and hand elements. Their similar basic structural plan indicates inheritance from a common ancestral limb, so they are homologous organs. The other options contradict their anatomy or definition.

Analogous organs perform similar functions but arise from different structural plans and evolutionary origins. A bird wing contains bones and muscles, whereas an insect wing is an extension of the exoskeleton. Both enable flight, so option A is correct. Option B describes neither their structure nor origin, option C refers incorrectly to homologous organs, and option D is biologically impossible.