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Q1. In the F₂ generation, short plants appeared in the ratio of
One quarterIn Mendel’s monohybrid cross (TT × tt → all Tt in F₁; F₁ self-cross Tt × Tt → F₂ genotypic ratio 1 TT : 2 Tt : 1 tt). Short plants (tt) appear in 1 out of 4 offspring, i.e., one quarter (25%). Half would be 2/4, three quarters would be 3/4, and all would be 4/4.
Q2. Mendel is known as the
Father of geneticsGregor Mendel established the fundamental laws of inheritance through his pea plant experiments. Darwin is the father of evolution, Aristotle is often called father of biology, and Theophrastus is father of botany.
Q3. Independent inheritance explains why traits
Appear in new combinationsIndependent assortment (Mendel’s second law) states that alleles of different genes segregate independently during gamete formation. This produces new combinations of traits in offspring (e.g., tall-wrinkled, short-round) not seen in parents. Traits do not disappear, mix permanently, or always remain linked.
Q4. The trait expressed in presence of another contrasting trait is called
DominantA dominant trait is expressed (visible) even when only one copy of its allele is present, i.e., in the presence of a contrasting (recessive) allele. Example: Tt plant is tall because T (tall) is dominant over t (short). Recessive traits require two copies.
Q5. Absence of medium-height plants in F₁ generation shows that
Only one trait is expressedWhen Mendel crossed tall (TT) and short (tt), all F₁ were tall (Tt). No medium plants appeared, proving that traits do not blend; instead, one trait (dominant) masks the other (recessive). Genes are not destroyed or lost; the recessive trait reappears in F₂.
Q6. Mendel selected pea plants because they
Show clear contrasting traitsPea plants have easily observable, distinct contrasting traits (e.g., tall/short, round/wrinkled, yellow/green). They also grow quickly, are annuals, and are easy to cultivate. Slow growth, perennial nature, and large size are not reasons; many plants are large but not suitable for genetic study.
Q7. The first generation produced by crossing parents is called
F₁ generationP (parental) generation is the original parents. F₁ (first filial) generation is the offspring of the P cross. F₂ is the offspring of crossing F₁ individuals. “Hybrid generation” is not a standard term; F₁ are hybrids but the specific name is F₁.
Q8. Which of the following is a contrasting trait studied by Mendel?
Tall and short plantsMendel studied seven contrasting traits in peas: stem height (tall/short), seed shape (round/wrinkled), seed color (yellow/green), flower position (axial/terminal), pod shape (inflated/constricted), pod color (green/yellow), and flower color (purple/white). Thick/thin stems, green/yellow leaves, and long/short roots were not among them.
Q9. A short pea plant appears only when the genotype is
ttShortness (dwarf) is recessive in pea plants. It is expressed only when both alleles are recessive (homozygous recessive, tt). Tt and TT produce tall plants because one T (dominant) is sufficient for tallness. TtTt is not a valid genotype notation.
Q10. Tallness and round seeds are considered
Dominant traitsIn Mendel’s experiments, tall stem (over short) and round seed shape (over wrinkled) are dominant traits. They are expressed in heterozygous condition. Recessive traits (short, wrinkled) appear only in homozygous recessive condition. They are not acquired or inherently harmful.
Q11. Efficient enzymes lead to
More hormoneEnzymes catalyze biochemical reactions, including hormone synthesis. Efficient (highly active or abundant) enzymes produce more hormone product. Less enzyme efficiency reduces hormone production. This explains how dominant alleles often produce functional enzymes leading to trait expression.
Q12. New combinations of traits arise mainly due to
Sexual reproductionSexual reproduction generates new trait combinations through crossing over (prophase I), independent assortment (metaphase I), and random fertilization. Mutations create new alleles but not new combinations. Asexual reproduction (including vegetative propagation) produces clones with no new combinations.
Q13. Mendel’s experiments were important because they
Explained inheritance scientificallyMendel’s work provided the first scientific, mathematical explanation of how traits are passed from parents to offspring, establishing the laws of segregation and independent assortment. He did not study respiration or growth primarily, and his work supported evolution (not disproved it).
Q14. Traits that are expressed only when both copies are identical are called
RecessiveRecessive traits require two identical copies of the recessive allele (homozygous recessive, e.g., tt) for expression. If one dominant allele is present, the dominant trait masks the recessive. Dominant traits require only one copy. Acquired and hybrid are not relevant.
Q15. The genetic makeup of an organism is called
GenotypeGenotype refers to the specific allelic composition of an organism (e.g., TT, Tt, tt). Phenotype is the physical appearance (tall or short). Variation is differences among individuals. Trait is a characteristic (e.g., height).
Q16. Each sexually reproducing organism inherits
Two copies of each traitDiploid organisms inherit two copies (alleles) of each gene—one from each parent. These two copies may be identical or different. One copy is present in gametes (haploid), but the offspring (zygote) receives two. Multiple random copies is incorrect; two is fixed.
Q17. Recessive traits are expressed only when
Both alleles are recessiveRecessive expression requires homozygosity (both alleles recessive, e.g., tt). If one dominant allele is present (Tt), the dominant trait masks the recessive. Hormone levels and enzyme efficiency are mechanisms but not the direct condition for expression.
Q18. Mendel conducted his experiments mainly on
Pea plantsMendel used Pisum sativum (garden pea) for his experiments due to its contrasting traits, self-pollination ability, ease of cross-pollination, short generation time, and large number of offspring. Wheat, rice, and maize were not his primary subjects.
Q19. Mendel was the first scientist to
Count individuals showing traitsMendel’s key innovation was quantitative analysis—counting large numbers of offspring and calculating ratios (e.g., 3:1, 9:3:3:1). He did not use microscopes extensively, did not study mutations, and DNA was discovered much later (1869 by Miescher, but its role in heredity was unknown).
Q20. All plants in the F₁ generation were
TallIn Mendel’s monohybrid cross (TT tall × tt short), all F₁ offspring were Tt (heterozygous). Since tall is dominant over short, all F₁ plants appeared tall. No medium or short plants appeared; wrinkled is a seed shape trait, not height.
Q21. Tall plants with genotype Tt are called
HeterozygousTt means the two alleles for the height gene are different (one T, one t). This is heterozygous. TT and tt are homozygous (pure). Recessive refers to the t allele, not the plant when T is present.
Q22. Mendel crossed plants with two different traits like
Height and seed shapeIn his dihybrid cross experiments, Mendel studied two traits simultaneously, e.g., seed shape (round/wrinkled) and seed color (yellow/green), or plant height and seed shape. He did not study leaf size, root length, or “height and colour” as a standard pair.
Q23. The tallness trait (T) in pea plants is
DominantTallness (T) is dominant over shortness (t). This means that a plant with at least one T allele (TT or Tt) will be tall. The t allele (short) is recessive and expressed only when homozygous (tt).
Q24. The amount of hormone produced depends on
Enzyme efficiencyHormone production is controlled by enzymatic reactions. Efficient (functional) enzymes produce normal or high levels of hormones; inefficient or non-functional enzymes (often from recessive alleles) produce reduced or no hormone. This explains dominance at the molecular level. Environment (temperature, soil, sunlight) influences but is not the primary determinant.
Q25. Tall plants of F₁ generation were tested by
Self-pollinationMendel allowed the F₁ tall plants (Tt) to self-pollinate to produce the F₂ generation. This revealed the reappearance of short plants (tt), proving that the recessive trait had not been lost. Cross-pollination is used for controlled crosses, not for producing F₂ from F₁.
Q26. All F₁ progeny from tall-round × short-wrinkled plants were
Tall and roundIn Mendel’s dihybrid cross, tall (T) is dominant over short (t), and round (R) is dominant over wrinkled (r). Parental: TTRR × ttrr → all F₁ are TtRr, expressing both dominant traits: tall and round. No wrinkled or short appear in F₁.
Q27. Mendel studied science and mathematics at
University of ViennaAfter joining the Augustinian monastery in Brno (now Czech Republic), Mendel was sent to the University of Vienna (1851-1853) where he studied physics, mathematics, and natural sciences. This training was crucial for his quantitative approach to heredity.
Q28. Which of the following combinations appeared in F₂ generation?
Tall-wrinkled and short-roundIn the F₂ of a dihybrid cross (TtRr × TtRr), the 9:3:3:1 ratio includes: 9 tall-round, 3 tall-wrinkled, 3 short-round, 1 short-wrinkled. Thus, new combinations (tall-wrinkled and short-round) appear that were not present in the original parents. Medium-height plants never appear.
Q29. Mendel’s work showed that inheritance is
Rule-basedMendel demonstrated that inheritance follows predictable mathematical laws (segregation, independent assortment), not blending (where traits mix) or pure randomness. While there is random chance in which gametes fuse, the overall patterns are rule-based. Environment influences expression but not the fundamental inheritance pattern.
Q30. A section of DNA that codes for one protein is called
GeneA gene is the basic functional unit of heredity—a specific sequence of DNA that codes for a polypeptide (protein) or functional RNA. Chromosomes contain many genes. Enzymes are proteins (gene products). Traits are characteristics influenced by genes.
Q31. Gregor Johann Mendel lived during the period
1822–1884Mendel was born in 1822 in Heinzendorf, Austria (now Czech Republic) and died in 1884. His famous pea plant experiments were conducted between 1856 and 1863, with publication in 1865-1866. 1900 is when his work was rediscovered (posthumously).
Q32. Mendel was initially educated in a
MonasteryMendel entered the Augustinian monastery in Brno (St. Thomas’s Abbey) in 1843, where he began his scientific work. He later studied at university (Vienna), but his initial education beyond basic schooling was within the monastery, which provided intellectual freedom and resources.
Q33. The physical appearance of a trait is called
PhenotypePhenotype is the observable physical or biochemical characteristic of an organism (e.g., tall, short, round, wrinkled). Genotype is the genetic makeup. A gene is a DNA segment. An allele is a variant form of a gene.
Q34. High hormone levels result in plants being
TallIn pea plants, the dominant allele (T) produces functional enzymes that synthesize gibberellins (plant growth hormones). High gibberellin levels promote stem elongation, resulting in tall plants. Recessive (tt) plants have non-functional enzymes, low hormone levels, and remain short.
Q35. Traits like seed shape and plant height are
Independently inheritedMendel’s law of independent assortment states that alleles of different genes (e.g., seed shape and plant height) segregate independently during gamete formation, provided they are on different chromosomes (or far apart on same chromosome). They are not always linked and are not acquired or purely environmental.
Q36. Mendel’s laws explain inheritance across
Many generationsMendel’s laws (segregation, independent assortment) apply to inheritance patterns across multiple generations. They predict ratios in F₁, F₂, F₃, and beyond. The principles are universal for sexually reproducing diploid organisms, not limited to one or two generations.
Q37. Appearance of short plants in F₂ generation proves that
Both traits were inheritedThe reappearance of short plants in F₂ (despite all F₁ being tall) proves that the short trait (recessive) was not lost or destroyed. It was inherited but masked in F₁. Both tall and short alleles were transmitted through the F₁ generation. DNA was not lost; short did not disappear permanently.
Q38. In the F₂ generation, new trait combinations appeared because
Traits were independently inheritedIn dihybrid crosses, new combinations (e.g., tall-wrinkled, short-round) arise due to independent assortment of alleles of different genes during gamete formation. Blending would not produce new combinations; mutations and DNA destruction are incorrect explanations.
Q39. Inefficient enzymes cause
Reduced hormone productionInefficient (non-functional or low-activity) enzymes catalyze reactions poorly, leading to reduced product formation. In pea plants, the recessive allele (t) produces a non-functional enzyme for gibberellin synthesis, resulting in low hormone levels and short stature. Extra chromosomes and increased growth are not direct effects.
Q40. TT and Tt genotypes both show
Tall plantsSince tall (T) is dominant over short (t), both homozygous dominant (TT) and heterozygous (Tt) genotypes produce the tall phenotype. Only the homozygous recessive (tt) produces short plants. Medium plants do not occur; wrinkled seeds are determined by a different gene.
Q41. Mendel’s experiment involving two traits is called
Dihybrid crossA dihybrid cross involves two traits (e.g., seed shape and seed color). A monohybrid cross involves one trait. A test cross is crossing an unknown dominant phenotype with a homozygous recessive. A back cross is crossing F₁ with one of the parents.
Q42. Dominant traits are expressed when
At least one dominant allele is presentA dominant trait is expressed in both homozygous dominant (TT) and heterozygous (Tt) conditions because the dominant allele produces a functional product (e.g., enzyme) sufficient for the trait. Recessive expression requires two recessive alleles. Hormone absence or enzyme inactivity would produce recessive phenotype.
Q43. Mendel’s failure in teaching examinations
Did not suppress his scientific zealMendel failed his teaching certification examinations twice (at the University of Vienna). Despite this setback, he continued his scientific research in the monastery with dedication, conducting his landmark experiments on pea plants. He did not quit science or lose interest.
Q44. Genes control traits by directing the formation of
ProteinsGenes (DNA sequences) are transcribed into mRNA and translated into proteins. These proteins (including enzymes, structural proteins, and hormones) carry out cellular functions that ultimately determine traits. While hormones are one type of protein signal, the broader answer is proteins. Cells and chromosomes are not directly “formed” by genes in this context.
Q45. Mendel’s careful counting helped him to
Formulate laws of inheritanceMendel’s quantitative approach—counting thousands of offspring and calculating precise ratios (3:1, 1:2:1, 9:3:3:1)—allowed him to deduce the laws of segregation and independent assortment. Chromosomes were identified later by others; evolution was Darwin’s domain; natural selection was not proven by Mendel.
Q46. Mendel crossed a tall pea plant with a
Short plantIn his classic monohybrid cross, Mendel crossed a tall pea plant (TT) with a short (dwarf) pea plant (tt). This produced the F₁ generation (all Tt, tall), followed by self-pollination to produce F₂. Weak, bushy, and medium plants were not standard contrasting traits.
Q47. Independent inheritance means
Traits are inherited separatelyIndependent inheritance (law of independent assortment) states that alleles of different genes segregate independently of each other during gamete formation. Thus, traits are inherited separately unless genes are linked on the same chromosome. Traits are not always linked, do not control each other, and do not disappear.
Q48. Plant height depends on
Plant hormonesPlant height is primarily regulated by hormones, particularly gibberellins. In peas, the T allele produces functional gibberellin synthesis enzymes, leading to tall growth. Leaf size, water, and root length can influence growth but are not the direct molecular determinant of the tall/short difference.
Q49. A single copy of ‘T’ makes a plant
TallThe T allele is dominant. A single copy (in heterozygous Tt condition) produces enough functional enzyme for gibberellin synthesis, making the plant tall. Medium plants do not occur in this system; wrinkled is a seed shape trait; short requires two copies of t.
Q50. The inheritance pattern of one trait is studied in
Monohybrid crossA monohybrid cross involves a single trait (e.g., plant height only or seed shape only). Dihybrid involves two traits. Polygenic cross involves multiple genes controlling one trait. Back cross is crossing F₁ with a parent. The basic 3:1 ratio in F₂ comes from a monohybrid cross.