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Q1. Mendel’s inheritance mechanism applies to
Sexually reproducing organismsMendel’s laws of inheritance (segregation, independent assortment) apply to all sexually reproducing, diploid organisms, including plants, animals, and humans. They do not apply to asexually reproducing organisms because there is no gamete fusion. The principles are universal for eukaryotic sexual reproduction.
Q2. Sex determination differs among
Different speciesSex determination mechanisms vary across species. Humans use XY system (males XY, females XX); birds use ZW system (females ZW, males ZZ); some reptiles use temperature-dependent sex determination; some plants have separate male/female individuals (dioecious). It is not uniform across all plants, chromosomes, or cells.
Q3. One gene set in a plant is inherited from
Each parentIn sexually reproducing plants (and animals), offspring inherit one set of genes (haploid set) from the male parent (pollen) and one set from the female parent (egg). Thus, each parent contributes equally. Environment does not contribute genetic material.
Q4. Variation during reproduction occurs due to
DNA errors and sexual reproductionVariations arise from two main sources: (1) DNA copying errors (mutations) that occur in all types of reproduction, and (2) sexual reproduction (crossing over, independent assortment, gamete fusion) which generates new combinations of existing alleles. Growth alone does not produce heritable variation.
Q5. Evolution is driven by
VariationEvolution requires heritable variation upon which natural selection acts. Without variation, all individuals would be identical, and no change in population characteristics could occur over generations. Uniformity, growth, and nutrition are not driving forces of evolutionary change.
Q6. A child inheriting X chromosome from father will be a
GirlHuman sex determination: females are XX, males are XY. The mother always contributes an X chromosome. If the father contributes an X (sperm with X), the child is XX (female). If the father contributes a Y, the child is XY (male). Intersex conditions are rare exceptions.
Q7. The Y chromosome is
Shorter than XThe human Y chromosome is significantly shorter than the X chromosome and contains fewer genes (approximately 200 vs. 1100 on X). It carries the SRY gene (sex-determining region Y) which triggers male development. It is not absent; it is present only in males.
Q8. Green beetles survive better because
They are camouflagedIn the classic beetle example, green beetles living on green leaves are less visible to predators (birds, lizards) than red beetles. Camouflage reduces predation, increasing survival and reproduction. This illustrates natural selection. Poison, speed, and reproduction rate are not the stated reason.
Q9. Evolution results in
Adapted populationsOver generations, natural selection increases the frequency of traits that enhance survival and reproduction in a given environment. This leads to populations becoming better adapted (fit) to their environment. Evolution does not reduce survival or create uniformity; it increases adaptation.
Q10. Probability of a child being a boy or a girl is
50% eachHuman sex determination: half of sperm carry X and half carry Y. The egg always carries X. The chance of X sperm fertilizing the egg (girl) is ~50%, and Y sperm (boy) is ~50%. The ratio is approximately equal. The mother does not fix the sex; it is determined by the father’s sperm.
Q11. Reduction of gene sets in germ cells is necessary to
Maintain chromosome numberMeiosis reduces the diploid (2n) chromosome number to haploid (n) in gametes. When two gametes fuse during fertilization, the diploid number is restored. Without this reduction, chromosome number would double each generation, which is unsustainable. Variation is a consequence, not the primary necessity.
Q12. During sexual reproduction, both parents contribute
Equal DNAEach parent contributes one haploid set of chromosomes (n) via gametes. Thus, the nuclear DNA contribution is equal (50% from each). Mitochondrial DNA is usually maternal only, but nuclear DNA is equal. “Only chromosomes” is too narrow (they contribute genes on chromosomes); “only traits” is vague.
Q13. Each germ cell receives
One chromosome from each pairDuring meiosis, homologous chromosomes separate. Each germ cell (gamete) receives one chromosome from each homologous pair, resulting in a haploid set (n). It does not receive only maternal or only paternal; it receives a mix. It does not receive all pairs (that would be diploid).
Q14. Predators of beetles in the example are
CrowsIn the standard textbook example of natural selection (often from NCERT), crows are the predators that eat red beetles more easily because they are visible on green leaves. Lizards, frogs, and snakes are possible predators but not the classic example.
Q15. Green colour in beetles is an example of
VariationGreen colour (versus red) is a heritable variation among beetles. Variations can arise from mutations or genetic recombination. “Mutation only” is too narrow because variation also comes from sexual reproduction. Acquired traits are not heritable; disease is incorrect.
Q16. Independent inheritance is possible because
Genes are on separate chromosomesMendel’s law of independent assortment applies to genes located on different chromosomes (or far apart on the same chromosome). These chromosomes segregate independently during meiosis. If genes are on the same chromosome and close together, they are linked (not independent). Chromosomes do exist; DNA in eukaryotes is linear, not circular.
Q17. Number of autosome pairs in humans is
22Humans have 23 pairs of chromosomes: 22 pairs of autosomes (non-sex chromosomes) and 1 pair of sex chromosomes (XX in females, XY in males). Total pairs = 23; autosome pairs = 22. 24, 23, and 21 are incorrect.
Q18. Asexual organisms also follow
Similar inheritance rulesAsexual organisms also pass genetic material from parent to offspring (inheritance), though without the recombination seen in sexual reproduction. The basic principle that traits are inherited via DNA applies. They do have DNA copying; inheritance is not random or absent.
Q19. Combination of two germ cells restores
Normal chromosome numberTwo haploid (n) germ cells (sperm and egg) fuse to form a diploid (2n) zygote, restoring the normal chromosome number for the species. Half chromosomes would be n; double DNA is vague (2n is normal, not double the normal). “No chromosomes” is incorrect.
Q20. Chromosomes exist in cells as
PairsIn diploid somatic cells, chromosomes exist as homologous pairs (one from each parent). Gametes have one copy (not pairs). Random fragments and many identical threads are incorrect descriptions. Pairs are the characteristic organization in most body cells.
Q21. If a gene produces a less efficient enzyme, the plant will be
ShorterIn pea plants, the recessive allele (t) produces a less efficient or non-functional enzyme for gibberellin (growth hormone) synthesis. Reduced gibberellin leads to shorter (dwarf) plants. This is a classic example of how gene function affects phenotype. Unchanged, dead, or taller are not correct.
Q22. In the beetle example, beetles reproduce by
Sexual reproductionIn the standard natural selection example, beetles reproduce sexually, producing offspring with genetic variation (green and red). This variation is essential for natural selection to act. Budding, asexual reproduction, and fragmentation produce clones with minimal variation.
Q23. Genes control characteristics mainly by
Controlling proteinsThe central dogma: genes (DNA) are transcribed to mRNA, which is translated into proteins. Proteins (enzymes, structural proteins, hormones) carry out cellular functions that ultimately determine characteristics (traits). Genes do not directly change chromosomes, alter tissues, or “make cells.”
Q24. Evolution occurs over
Many generationsEvolution is the change in allele frequencies in a population over successive generations. It is not observable in a single generation, season, or lifetime (except in very fast-reproducing organisms like bacteria under selection). It requires accumulation of heritable changes across many generations.
Q25. Humans have how many pairs of chromosomes?
23Humans have 23 pairs of chromosomes (46 total). This includes 22 pairs of autosomes and 1 pair of sex chromosomes. 24 pairs would be 48 (found in some apes), 22 pairs would be 44 (found in some other species). 21 is incorrect.
Q26. All children inherit which chromosome from their mother?
XMothers have two X chromosomes (XX). They always pass one X chromosome to all children (both sons and daughters). The father contributes either X (daughter) or Y (son). Thus, every child inherits an X from the mother. Y comes only from father.
Q27. Asexually reproducing organisms show
Limited variationAsexual reproduction produces genetically identical offspring (clones). Variation is limited to rare mutations that occur during DNA replication. This is much lower than the variation generated by sexual reproduction. “No variation” is incorrect because mutations do occur; “high variation” is false.
Q28. Each chromosome pair contains
One maternal and one paternal copyHomologous chromosomes are pairs consisting of one chromosome inherited from the mother and one from the father. They carry the same genes but may have different alleles. Two maternal or two paternal copies would indicate abnormal chromosome complement. Only dominant genes is false.
Q29. Beetles live on bushes with
Green leavesIn the classic natural selection example, green beetles survive better because they are camouflaged on green leaves. Red beetles stand out and are eaten more by predators. The leaf color is green, matching the advantageous beetle color. Red, yellow, or brown leaves would change the selection pressure.
Q30. Red beetles are eaten more because
They are visibleOn green leaves, red beetles are highly visible to predators (crows), while green beetles are camouflaged. Visibility leads to higher predation. Size, genes (they have genes), and weakness are not the primary reasons in this example.
Q31. Traits that help survival are
SelectedTraits that increase survival and reproduction are “selected” by the environment (natural selection). They become more common in the population over generations. Harmful traits are eliminated. Neutral traits may be ignored. Selected traits are not destroyed.
Q32. This beetle example explains
Natural selectionThe beetle example (green vs. red beetles on green leaves, with crows eating more red beetles) is a classic illustration of natural selection: variation, differential survival, and inheritance leading to change in population over time. It does not primarily explain reproduction, growth, or nutrition.
Q33. Genes are present as parts of
ChromosomesGenes are specific sequences of DNA located on chromosomes within the nucleus (and also in mitochondria/chloroplasts). Cytoplasm contains organelles but not genes as organized structures; proteins and enzymes are products of genes, not locations.
Q34. Sex of the child is determined by
FatherIn humans, the mother always contributes an X chromosome. The father contributes either X (producing a girl) or Y (producing a boy). Thus, the sex of the child is determined by which sex chromosome the father’s sperm carries. Environment and nutrition do not determine sex in humans.
Q35. Chromosomes ensure
Orderly inheritanceChromosomes are the physical structures that carry genes. Their behavior during meiosis (segregation, independent assortment) and fertilization ensures that genetic material is transmitted in an orderly, predictable manner from parents to offspring. Loss of traits is not ensured; inheritance is not random or absent.
Q36. Each pea plant has
Two sets of genesPea plants, like most eukaryotes, are diploid. They have two sets of genes (2n), one inherited from the male parent (pollen) and one from the female parent (egg). Each set is a complete haploid genome. No genes is false; multiple random sets is incorrect (they have exactly two).
Q37. Some animals like snails can
Change sexSome animals, including certain snails (e.g., slipper limpets), are sequential hermaphrodites that can change sex during their lifetime (e.g., from male to female or vice versa). Colour change, stopping reproduction, and changing genes (mutation) are not the specific example referenced.
Q38. Sex chromosomes in males are
XYIn humans and most mammals, males have one X and one Y chromosome (XY). Females have XX. YY is non-viable in humans. XO is Turner syndrome (female with one X). XX is female. XY is the normal male karyotype.
Q39. Sex determination in humans is an example of
Genetic determinationHuman sex determination is genetically determined by the presence or absence of the Y chromosome (specifically the SRY gene). It is not influenced by environment (unlike some reptiles where temperature determines sex). It is not a mutation or acquired trait.
Q40. Harmful variations are usually
EliminatedHarmful (deleterious) variations reduce survival or reproduction. Natural selection acts against them, causing them to be eliminated from the population over generations. They are not inherited forever (though they can persist at low frequency if recessive), not selected for, and not necessarily dominant.
Q41. Selection by environment forms the basis of
EvolutionNatural selection (environment selecting advantageous variations) is the primary mechanism of evolution. Genetics is the study of inheritance, growth is increase in size, heredity is transmission of traits. While related, selection specifically drives evolutionary change.
Q42. In humans, sex is mainly determined by
GenesHuman sex determination is genetic, primarily by the SRY gene on the Y chromosome. Hormones are downstream products of gene expression. Environment and nutrition do not determine sex in humans (unlike some reptiles). The correct answer is “Genes.”
Q43. Germ cells contain
One gene setGerm cells (gametes: sperm and egg) are haploid (n), containing one set of genes (one copy of each chromosome). Two gene sets (2n) is the diploid condition in somatic cells. No genes or three sets are incorrect.
Q44. Advantageous variations lead to
SurvivalAdvantageous (beneficial) variations increase an organism’s chance of surviving and reproducing in its environment. Over generations, these traits become more common. Reduced population, extinction, and no change are opposite outcomes.
Q45. A child inheriting Y chromosome from father will be a
BoyThe Y chromosome carries the SRY gene, which triggers male development. A child who inherits Y from the father (and X from the mother) is XY and develops as male (boy). Girls inherit X from father. Hermaphrodite and sterile are not the general outcome.
Q46. Over generations, green beetles become
More numerousIn the beetle example, green beetles are camouflaged and survive better. They reproduce more, and their offspring (also green) increase in proportion. Over generations, the green population becomes more numerous, while red beetles decrease. Extinction of red may occur if selection is strong.
Q47. Stability of species DNA is maintained by
Equal chromosome contributionSexual reproduction with equal chromosome contribution from each parent (via meiosis and fertilization) maintains the species-specific chromosome number and genetic makeup across generations. Environmental changes and mutations disrupt stability; unequal inheritance would cause instability.
Q48. Sex chromosomes in females are
XXIn the human XY sex-determination system, females have two X chromosomes (XX). XO is Turner syndrome (females with one X). YY is non-viable. XY is male. Thus, XX is the normal female karyotype.
Q49. The combined study of heredity and evolution explains
Diversity of lifeHeredity (inheritance of traits) and evolution (change over time) together explain how diverse life forms arose from common ancestors through variation, selection, and speciation. Respiration, excretion, and digestion are physiological processes, not explained by heredity+evolution.
Q50. In some animals, sex is determined by
TemperatureIn many reptiles (alligators, turtles, some lizards) and some fish, sex is determined by the temperature during egg incubation (temperature-dependent sex determination, TSD). Food, size, and “genes only” are not correct for these species; they have genetic sex determination (e.g., XY, ZW) but TSD is a notable exception.