Heredity and Evolution

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 heredity: an inherited trait is transmitted from parents to offspring through genetic information. Eye colour may be determined partly by genes received from both parents, so it is an appropriate example of an inherited trait. Learning to cycle is a learned behaviour, while a wound and exercise-built muscles are acquired changes that are not normally passed genetically to children.

The governing concept is the difference between inherited and acquired traits. Darkening of skin after exposure to sunlight develops during an individual’s lifetime because of an environmental influence, so it is an acquired change. Blood group and genetically controlled eye colour are inherited characteristics, while chromosome number is a genetic feature rather than a lifetime-acquired trait. Sun tanning normally does not alter reproductive-cell DNA in a heritable way.

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.

Fossils are preserved remains, impressions, or traces of organisms that lived in the past. Fossils from different rock layers reveal the kinds of organisms that existed at different times and show gradual structural changes. Therefore option A correctly describes their value as evolutionary evidence. Weather, blood groups, and food taste are not established by fossils in this way.

In undisturbed sedimentary rock, layers are usually deposited one above another, so deeper layers formed earlier than upper layers. Fossils preserved in those deeper layers therefore generally belong to organisms that lived earlier. Option A is correct. The other choices reverse the relative-age principle or do not describe biological fossils at all.

Genetic drift is a random change in the frequency of alleles, and sampling effects are proportionally larger in a small population. If only a few individuals reproduce or survive, their alleles can become common or disappear simply by chance. Therefore option A is correct. Small populations do have genes, can reproduce, and are not necessarily identical.

Evolution refers to inherited changes in populations across successive generations, not to temporary changes in one individual's body. These changes can alter traits and population characteristics over long periods. Option A gives the correct definition. Muscle growth is an individual lifetime change, evolution does not always produce greater complexity, and cooking has no biological connection to the term.

Evolution means change in inherited characteristics over generations, not movement toward a fixed idea of superiority or complexity. A simple organism may be very well adapted to its environment and survive successfully, while a complex organism may not. Thus option A is correct. The other statements deny evolution, assume universal superiority, or wrongly restrict it to humans.

A variation is inherited only when the relevant genetic change is present in reproductive cells or their genetic material, because these cells contribute hereditary information to offspring. A wound, exercise-built muscle, or learned habit affects the individual but does not normally alter the genes passed to children. Therefore option A is correct.

Copying genetic material can occasionally introduce a small change, or mutation, creating variation. Its effect depends on the gene and the environment: it may be neutral, harmful, or sometimes beneficial. Therefore option A is correct. A copying error does not automatically kill the organism, remove chromosomes, or stop reproduction in every case.