Heredity and Evolution

Natural selection depends on the relationship between a trait and environmental conditions. A feature that improves survival in one setting may become neutral or disadvantageous after the surroundings change, while another feature may become useful. Individuals with the newly advantageous heritable trait may leave more offspring, shifting its frequency. Thus A is correct; B, C, and D deny environmental effects or biological variation.

Green colour can provide camouflage on green leaves, making those insects less visible to birds. If the colour is heritable, better survival can lead to greater reproduction, so the green variant may become more frequent in later generations. This differential survival and reproduction is natural selection, making A correct. The example does not show acquired-trait inheritance, blending, or chromosome loss.

The governing concept is the distinction between homologous and analogous organs. Analogous organs may perform a similar function because organisms face similar environmental demands, but their basic structure and evolutionary origin are different. Thus wings of insects and birds both help in flight, yet they do not by themselves indicate a common structural origin. Therefore option A is correct; colour, lack of function, and occurrence only in humans are unrelated claims.

Homologous organs share a basic structural plan and common evolutionary origin, even if their functions differ. A bird wing is a modified, bony forelimb, whereas an insect wing is an outgrowth of the body wall with a different construction and origin. Their shared function, flight, therefore represents analogy rather than homology. Option A is correct; the other choices deny flight or incorrectly claim a shared bone plan or organism.

Distance can reduce contact, but it does not by itself prove that two populations have become separate species. If separated groups meet again and produce fertile, viable offspring, gene flow can continue. Reproductive isolation—before mating, during fertilisation, or after offspring formation—prevents successful gene exchange and makes divergence biologically meaningful. Therefore option A is correct; the other statements incorrectly describe distance or isolation.

Classification groups organisms according to observable and, increasingly, structural, developmental, and molecular similarities. Shared detailed features can suggest common ancestry and help scientists construct evolutionary relationships. However, classification is an organised interpretation of similarities, not independent proof by itself. Fossils, comparative anatomy, embryology, and molecular evidence strengthen the conclusion. Option A is correct; the other choices wrongly deny its evolutionary value or oversimplify its basis.

External resemblance may result from analogous adaptation: unrelated organisms can develop similar shapes or parts because they perform similar functions in comparable environments. This is called convergent evolution and does not necessarily indicate close ancestry. Reliable evolutionary comparison also considers internal anatomy, development, fossils, and molecular evidence. Option A is correct because it identifies the difference between functional similarity and shared structural origin; the other choices are false or overgeneralised.

Evolution means a change in the inherited characteristics or allele frequencies of a population across generations. An individual can grow, learn, or acquire a change during its lifetime, but such an acquired change is not automatically inherited by offspring. When inherited variation affects survival and reproduction, its frequency may increase or decrease in the population. Therefore option A is correct; the distractors incorrectly deny individual changes, reproduction, or the timescale of evolution.

Darwin’s concept of struggle for existence follows from the fact that populations can produce more offspring than available food, space, shelter, and other resources can support. Because resources are limited, individuals compete, and those with heritable traits better suited to the environment are more likely to survive and reproduce. Their traits may become more common. Option A is correct; limited resources do not create identical organisms, erase genes instantly, or cause immortality.

The governing concept is natural selection acting on heritable variation. An adaptive trait gives some organisms an advantage in survival or reproduction under particular environmental conditions. Those organisms are more likely to leave offspring, so the associated trait may become more common over generations. Natural selection does not create every adaptation instantly or remove useful traits; therefore option A correctly describes the relation.

Fossils provide a time-ordered record of organisms and can reveal changes in forms that lived in the past. Homologous organs have a similar basic structural plan, even when their functions differ, suggesting common ancestry. When both types of evidence are considered together, they support change over generations and relationships among organisms. Thus option A is correct; the other choices confuse evolutionary evidence with feeding, acquired traits, or sex determination.

Evolution concerns changes in inherited characteristics of populations across generations. A colour difference can be useful, but it contributes to evolution only if the genetic information responsible for it can pass through reproductive cells to offspring. A change acquired during an individual’s lifetime is generally not inherited merely because it is useful. Therefore option A is correct; options B, C and D prevent the trait from being reliably transmitted between generations.

Natural selection depends on the interaction between existing variation and environmental conditions. Different environments present different challenges, such as temperature, food availability, predators or disease. A trait that improves survival or reproduction in one environment may provide little benefit, or even a disadvantage, in another. Over generations, selection can therefore increase different heritable traits in the two populations. Hence option A is correct; the other options deny variation or misunderstand selection.

Homologous organs are identified by a common basic structural plan and evolutionary origin, not by identical present-day use. The bones of the human forelimb and bird forelimb correspond in arrangement, but natural selection has modified them for different functions. A human hand is mainly adapted for grasping and manipulation, whereas a bird wing is adapted for flight. Therefore option A is correct; homology does not require functional identity.

Natural selection changes trait frequencies through differential reproductive success. A useful trait may help an organism avoid predators, obtain food or tolerate conditions, which supports survival. However, the trait can become more common only if the surviving organism reproduces and passes the relevant heritable information to offspring. Survival without reproduction does not increase the next generation’s frequency, and reproduction without survival cannot occur. Therefore option A correctly combines both requirements.

The governing concept is that heredity transmits genetic information from parents to offspring, while variation creates differences among individuals. Some of these variations are inherited and may become more common through natural selection, genetic drift, or isolation. Across many generations, such changes can produce evolution. Therefore, option A is correct; the other options deny the role of inheritance or confuse these biological processes with digestion.

A balanced conclusion must include both continuity and change. Genes transmit information for traits from one generation to the next, establishing heredity. At the same time, inherited variation produces differences in a population. Natural selection, genetic drift, and reproductive or geographical isolation can change the frequency of these differences over many generations, producing evolution. Thus option A is correct; the other choices contradict established genetic principles.

Let T represent the dominant tall allele and t the recessive dwarf allele. A hybrid tall plant has genotype Tt. In the cross Tt × Tt, the possible combinations are TT, Tt, Tt, and tt. The tt offspring receive the recessive allele from both parents and therefore show the dwarf phenotype. Thus option A is correct; tallness is not destroyed and the environment does not create this inherited combination.

The 3:1 phenotypic ratio in the F2 generation is characteristic of a monohybrid cross between two heterozygotes, such as Tt × Tt. The alleles separate when gametes form, and fertilisation recombines them. The genotypic ratio is 1 TT:2 Tt:1 tt, which produces a 3 tall:1 dwarf phenotype ratio when T is dominant. Hence option A is correct; recessive alleles are hidden, not erased.

In the Mendelian pea example, tallness is dominant and dwarfness is recessive. A dominant allele would mask a recessive dwarf allele in a heterozygous plant, so a plant showing the dwarf phenotype cannot contain a dominant tall allele for that trait. Its genotype must therefore be tt, with two recessive alleles. Option A is correct; genes are present, and the phenotype is not explained as merely an acquired change.