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Tamil Nadu HSE Second Year Biology study materials
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Tamil Nadu HSE Second Year Biology practice questions

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Question 1Reproduction (sexual and asexual reproduction in plants and animals, human reproductive system, reproductive health)

In the life cycle of a flowering plant, which structure develops directly from the zygote after double fertilization?

  1. The nucellus of the ovule
  2. The embryo of the seed Correct answer.
  3. The integument of the ovule
  4. The endosperm of the seed

Explanation

Double fertilization produces a diploid zygote and a triploid primary endosperm nucleus. The zygote undergoes mitotic divisions to form the embryo, while the primary endosperm nucleus gives rise to the nutritive endosperm. Integuments become the seed coat and the nucellus is the tissue enclosing the embryo sac.

Question 2Reproduction (sexual and asexual reproduction in plants and animals, human reproductive system, reproductive health)

Which of the following is a characteristic feature of asexual reproduction in organisms such as Hydra and yeast?

  1. Fusion of gametes from two parents
  2. Production of offspring genetically identical to the parent Correct answer.
  3. Recombination of genes during crossing over
  4. Formation of haploid spores by meiosis

Explanation

Asexual reproduction involves a single parent and no fusion of gametes, so the offspring are genetically identical clones of the parent. Hydra reproduces by budding and yeast by budding as well, both mitotic processes. Gamete fusion, meiotic spore formation and crossing over all introduce genetic variation and belong to sexual reproduction.

Question 3Reproduction (sexual and asexual reproduction in plants and animals, human reproductive system, reproductive health)

The transfer of pollen grains from the anther of a flower to the stigma of another flower on a different plant of the same species is called

  1. Cleistogamy
  2. Autogamy
  3. Xenogamy Correct answer.
  4. Geitonogamy

Explanation

Xenogamy is cross-pollination between two different plants of the same species, bringing genetically different pollen to the stigma. Geitonogamy is pollen transfer between flowers of the same plant, and autogamy is self-pollination within the same flower. Cleistogamy refers to flowers that never open and are obligately self-pollinated.

Question 4Reproduction (sexual and asexual reproduction in plants and animals, human reproductive system, reproductive health)

In humans, the secondary oocyte is released from the ovary at ovulation while arrested at which stage of meiosis?

  1. Anaphase I
  2. Prophase I
  3. Telophase II
  4. Metaphase II Correct answer.

Explanation

The oocyte completes the first meiotic division just before ovulation, producing a secondary oocyte that remains arrested at metaphase II. Meiosis II is completed only if a sperm penetrates the secondary oocyte, releasing the second polar body. Prophase I arrest occurs much earlier, during fetal life, in the primary oocyte.

Question 5Reproduction (sexual and asexual reproduction in plants and animals, human reproductive system, reproductive health)

Which hormone surge directly triggers ovulation in the human menstrual cycle?

  1. Progesterone
  2. Prolactin
  3. Luteinising hormone Correct answer.
  4. Follicle-stimulating hormone

Explanation

A sharp mid-cycle surge of luteinising hormone from the anterior pituitary ruptures the mature Graafian follicle and releases the oocyte. FSH mainly stimulates follicular growth, progesterone supports the luteal phase, and prolactin promotes milk secretion.

Question 6Reproduction (sexual and asexual reproduction in plants and animals, human reproductive system, reproductive health)

The surgical procedure in which the vas deferens is cut and tied to prevent sperm from reaching the urethra is known as

  1. Vasectomy Correct answer.
  2. Laparoscopy
  3. Tubectomy
  4. Hysterectomy

Explanation

Vasectomy is a male sterilisation method in which each vas deferens is cut and ligated so that sperm cannot enter the ejaculate. Tubectomy is the corresponding female procedure involving the fallopian tubes. Hysterectomy removes the uterus and laparoscopy is only a visualisation technique.

Question 7Reproduction (sexual and asexual reproduction in plants and animals, human reproductive system, reproductive health)

Which of the following sexually transmitted infections is caused by a bacterium rather than a virus?

  1. Hepatitis B
  2. Genital herpes
  3. Genital warts
  4. Gonorrhoea Correct answer.

Explanation

Gonorrhoea is caused by the bacterium Neisseria gonorrhoeae and responds to antibiotic therapy. Genital herpes, genital warts and hepatitis B are all viral infections caused by herpes simplex, human papillomavirus and hepatitis B virus respectively.

Question 8Reproduction (sexual and asexual reproduction in plants and animals, human reproductive system, reproductive health)

In a dicot embryo, the part that develops into the future root is the

  1. Epicotyl
  2. Plumule
  3. Radicle Correct answer.
  4. Cotyledon

Explanation

The embryonic axis of a dicot seed has a radicle at the lower end that grows into the primary root, and a plumule at the upper end that forms the shoot. Cotyledons are food-storing seed leaves, and the epicotyl is the region above the cotyledonary node.

Question 9Reproduction (sexual and asexual reproduction in plants and animals, human reproductive system, reproductive health)

A pollen grain that lands on a compatible stigma germinates and produces a pollen tube. Which tissue does the tube normally traverse to reach the ovule?

  1. The style and transmitting tissue Correct answer.
  2. The seed coat of the ovule
  3. The cotyledons of the embryo
  4. The endosperm of the ovule

Explanation

After germination on the stigma, the pollen tube grows down through the style, often along the transmitting tissue, and enters the ovary to reach the micropyle of the ovule. Endosperm, seed coat and cotyledons are post-fertilisation structures that do not exist when the tube is growing.

Question 10Reproduction (sexual and asexual reproduction in plants and animals, human reproductive system, reproductive health)

Which structure of the human male reproductive system secretes an alkaline fluid that neutralises the acidity of the vagina and contributes to semen?

  1. Seminal vesicles
  2. Bulbourethral glands
  3. Epididymis
  4. Prostate gland Correct answer.

Explanation

The prostate gland secretes a slightly alkaline fluid that helps neutralise vaginal acidity and supports sperm motility in semen. The seminal vesicles contribute fructose-rich fluid, bulbourethral glands secrete a lubricating mucus, and the epididymis stores and matures sperm without adding alkaline secretion.

Question 11Reproduction (sexual and asexual reproduction in plants and animals, human reproductive system, reproductive health)

The site of fertilisation in the human female reproductive tract is normally the

  1. Cervix
  2. Ampulla of the fallopian tube Correct answer.
  3. Fundus of the uterus
  4. Cervical canal

Explanation

Fertilisation usually occurs in the ampullary region of the fallopian tube, where sperm meet the secondary oocyte after ovulation. The zygote then travels to the uterus for implantation. The cervix and fundus are not the normal site of gamete fusion.

Question 12Reproduction (sexual and asexual reproduction in plants and animals, human reproductive system, reproductive health)

Implantation of the human blastocyst into the endometrium normally begins about how many days after fertilisation?

  1. Day 21 to day 22
  2. Day 6 to day 7 Correct answer.
  3. Day 1 to day 2
  4. Day 14 to day 15

Explanation

The zygote undergoes cleavage while travelling down the fallopian tube and reaches the uterus as a blastocyst. Implantation into the prepared endometrium begins around the sixth to seventh day after fertilisation. By day 14 the embryo is already implanted and the decidual reaction is established.

Question 13Reproduction (sexual and asexual reproduction in plants and animals, human reproductive system, reproductive health)

Which of the following is a natural method of contraception that relies on avoiding intercourse during the fertile window of the menstrual cycle?

  1. Condom use
  2. Rhythm method Correct answer.
  3. Lactational amenorrhoea
  4. Coitus interruptus

Explanation

The rhythm or calendar method avoids coitus during the days when ovulation is likely, based on the regularity of the menstrual cycle. Lactational amenorrhoea depends on breastfeeding-induced suppression of ovulation, coitus interruptus withdraws before ejaculation, and condoms are barrier devices.

Question 14Reproduction (sexual and asexual reproduction in plants and animals, human reproductive system, reproductive health)

In angiosperms, the megaspore mother cell undergoes meiosis to produce four megaspores. In the typical Polygonum type of embryo sac, how many of these megaspores remain functional?

  1. Four
  2. Two
  3. Three
  4. One Correct answer.

Explanation

In the monosporic Polygonum type, only the chalazal megaspore survives while the other three degenerate. The functional megaspore undergoes three mitotic divisions to form the eight-nucleate, seven-celled embryo sac. All four megaspores remaining functional would describe a tetrasporic type, which is not typical.

Question 15Reproduction (sexual and asexual reproduction in plants and animals, human reproductive system, reproductive health)

Which of the following pairs correctly matches an animal with its mode of asexual reproduction?

  1. Planaria - budding
  2. Yeast - multiple fission
  3. Amoeba - binary fission Correct answer.
  4. Hydra - fragmentation

Explanation

Amoeba reproduces asexually by binary fission, in which the parent cell divides into two daughter cells. Hydra reproduces mainly by budding, Planaria by regeneration and fragmentation, and yeast by budding rather than multiple fission.

Question 16Reproduction (sexual and asexual reproduction in plants and animals, human reproductive system, reproductive health)

A student observes that a flower has large, brightly coloured petals, a sweet scent and nectar, but its stigma is sticky and hangs outside the anther. Which pollinating agent is most likely involved?

  1. Wind
  2. Water
  3. Bats only at night
  4. Insects Correct answer.

Explanation

Bright petals, scent and nectar are classic adaptations to attract insect pollinators, which transfer pollen as they forage. Wind-pollinated flowers are small, dull and nectarless with feathery stigmas, and water-pollinated flowers release pollen into water. The combination described therefore points to entomophily.

Question 17Reproduction (sexual and asexual reproduction in plants and animals, human reproductive system, reproductive health)

In humans, the corpus luteum of the ovary is maintained by which hormone during the luteal phase?

  1. Luteinising hormone Correct answer.
  2. Follicle-stimulating hormone
  3. Oxytocin
  4. Antidiuretic hormone

Explanation

After ovulation, luteinising hormone supports the corpus luteum, which secretes progesterone and oestrogen to maintain the endometrium. If pregnancy does not occur, the corpus luteum degenerates and menstruation follows. FSH acts earlier on follicular growth, while oxytocin and antidiuretic hormone are unrelated to luteal maintenance.

Question 18Reproduction (sexual and asexual reproduction in plants and animals, human reproductive system, reproductive health)

In humans, the gametes are produced by meiosis, and a primary spermatocyte gives rise to how many functional spermatozoa?

  1. Eight
  2. Two
  3. One
  4. Four Correct answer.

Explanation

One primary spermatocyte completes meiosis I and II to yield four haploid spermatids, all of which mature into functional spermatozoa. In oogenesis, by contrast, one primary oocyte yields only one functional ovum plus polar bodies. The number four reflects the two successive meiotic divisions without further multiplication.

Question 19Reproduction (sexual and asexual reproduction in plants and animals, human reproductive system, reproductive health)

Which of the following statements about the human placenta is correct?

  1. It is derived purely from maternal tissue.
  2. It first appears in the second trimester.
  3. It allows direct mixing of maternal and fetal blood.
  4. It secretes human chorionic gonadotropin, which maintains the corpus luteum. Correct answer.

Explanation

The placenta is a chorioallantoic structure with both fetal and maternal components and secretes human chorionic gonadotropin, which sustains the corpus luteum in early pregnancy. Maternal and fetal blood are separated by placental membranes and never mix directly. The placenta is functional from early in pregnancy.

Question 20Reproduction (sexual and asexual reproduction in plants and animals, human reproductive system, reproductive health)

Which of the following is an assisted reproductive technique in which sperm is directly injected into the cytoplasm of an oocyte under a microscope?

  1. Intrauterine insemination
  2. Intracytoplasmic sperm injection Correct answer.
  3. Zygote intrafallopian transfer
  4. Gamete intrafallopian transfer

Explanation

Intracytoplasmic sperm injection involves microinjection of a single sperm directly into the cytoplasm of a mature oocyte, and is used when sperm count or motility is very poor. Intrauterine insemination places semen in the uterus, while ZIFT and GIFT involve transfer of zygotes or gametes into the fallopian tube.

Question 21Reproduction (sexual and asexual reproduction in plants and animals, human reproductive system, reproductive health)

A couple is advised to use a barrier method that also provides protection against sexually transmitted infections. Which method best fits this advice?

  1. Oral contraceptive pills
  2. Copper intrauterine device
  3. Condom Correct answer.
  4. Tubectomy

Explanation

Condoms are physical barriers that prevent sperm from meeting the oocyte and also reduce transmission of many sexually transmitted pathogens. Hormonal pills, intrauterine devices and sterilisation prevent pregnancy but do not protect against infection. Hence only the barrier method satisfies both requirements.

Question 22Reproduction (sexual and asexual reproduction in plants and animals, human reproductive system, reproductive health)

In a flowering plant, the endosperm of a typical angiosperm seed is triploid because it is formed by the fusion of

  1. One male gamete with two polar nuclei Correct answer.
  2. The egg cell with a synergid
  3. Two male gametes with the egg cell
  4. One male gamete with the egg cell

Explanation

Triple fusion in double fertilisation joins one male gamete with the two polar nuclei of the central cell, giving a triploid primary endosperm nucleus. Fusion of a male gamete with the egg cell produces the diploid zygote, not endosperm. Fusion of egg with synergid is not a normal fertilisation event.

Question 23Reproduction (sexual and asexual reproduction in plants and animals, human reproductive system, reproductive health)

In the human menstrual cycle, the endometrium enters the proliferative phase and thickens mainly in response to

  1. Falling progesterone after corpus luteum regression
  2. Rising oestrogen from developing follicles Correct answer.
  3. Rising prolactin from the anterior pituitary
  4. Falling luteinising hormone after ovulation

Explanation

After menstruation, developing ovarian follicles secrete increasing oestrogen, which stimulates proliferation and thickening of the endometrium. Progesterone from the corpus luteum later converts it to the secretory phase. Falling progesterone causes shedding of the endometrium, not its proliferation.

Question 24Reproduction (sexual and asexual reproduction in plants and animals, human reproductive system, reproductive health)

Which of the following correctly explains why self-pollination reduces genetic variation in a plant population?

  1. It involves the fusion of gametes carrying identical alleles from the same plant. Correct answer.
  2. It always results in polyploid offspring that cannot reproduce.
  3. It prevents the formation of pollen grains in the anther.
  4. It produces seeds without fertilisation and therefore without meiosis.

Explanation

In self-pollination, the male and female gametes come from the same plant, so many loci are homozygous and the offspring closely resemble the parent. This reduces the reshuffling of alleles that cross-pollination provides. Self-pollination does not bypass fertilisation or meiosis, nor does it prevent pollen formation.

Question 25Reproduction (sexual and asexual reproduction in plants and animals, human reproductive system, reproductive health)

A woman with a regular 28-day menstrual cycle has her last menstrual period begin on day 1. Ovulation is most likely to occur around which day?

  1. Day 14 Correct answer.
  2. Day 28
  3. Day 21
  4. Day 7

Explanation

In a regular 28-day cycle, ovulation occurs approximately midway, around day 14, about 14 days before the next menstruation. The follicular phase precedes it and the luteal phase follows it. Day 7 is still follicular, day 21 is luteal, and day 28 marks the onset of the next menstruation.

Question 26Reproduction (sexual and asexual reproduction in plants and animals, human reproductive system, reproductive health)

In the human female reproductive system, which structure is the narrow lower portion of the uterus that opens into the vagina?

  1. Fundus
  2. Myometrium
  3. Cervix Correct answer.
  4. Fimbriae

Explanation

The uterus has a broad upper body (with the fundus above the openings of the fallopian tubes) and a narrow neck-like lower part, the cervix, which projects into the vagina. The cervix contains the cervical canal that connects the uterine cavity with the vaginal lumen and secretes mucus whose consistency changes across the menstrual cycle.

Question 27Reproduction (sexual and asexual reproduction in plants and animals, human reproductive system, reproductive health)

A plant species reproduces by producing bulbils in the axils of its leaves; each bulbil detaches and grows into a new plant. Which statement best describes the genetic outcome of this mode of reproduction?

  1. The offspring differ from the parent because bulbils develop from unfertilised egg cells
  2. The offspring are genetically identical to the parent because the bulbils arise by mitosis from somatic tissue Correct answer.
  3. The offspring are haploid throughout their life because no fusion of gametes occurs
  4. The offspring show new gene combinations because bulbils are formed after meiosis and fertilisation

Explanation

Bulbils are vegetative propagules produced by mitotic division of somatic tissue of the parent plant, so they carry the same chromosome complement and alleles as the parent. Because no meiosis, gamete fusion or recombination is involved, the resulting plants are clones and the mode is asexual.

Question 28Reproduction (sexual and asexual reproduction in plants and animals, human reproductive system, reproductive health)

In a flowering plant, a mutation makes the synergids unable to release calcium signals and prevents the pollen tube from bursting. Which event of double fertilisation would be blocked first?

  1. Differentiation of the integuments into the seed coat after fertilisation
  2. Meiosis of the megaspore mother cell to produce four megaspores
  3. Discharge of the two male gametes into the embryo sac, so neither syngamy nor triple fusion can occur Correct answer.
  4. Formation of the pollen tube by the generative cell within the style

Explanation

The pollen tube enters the embryo sac through the filiform apparatus of a synergid and bursts there, releasing the two male gametes into the sac. Only after this discharge can one male gamete fuse with the egg (syngamy) and the other with the two polar nuclei (triple fusion). If tube rupture fails, both fusion events are prevented.

Question 29Genetics and Evolution (Mendelian genetics, molecular basis of inheritance, evolution)

In a dihybrid cross between two heterozygous pea plants (RrYy × RrYy), what is the expected phenotypic ratio of the offspring?

  1. 1:1:1:1
  2. 9:3:3:1 Correct answer.
  3. 1:2:1
  4. 3:1

Explanation

When two genes assort independently and both parents are heterozygous, the F2 phenotypic ratio is 9:3:3:1, where 9 shows both dominant traits, 3 shows one dominant and one recessive, another 3 shows the reciprocal, and 1 shows both recessive traits.

Question 30Genetics and Evolution (Mendelian genetics, molecular basis of inheritance, evolution)

Which molecule serves as the genetic material in the majority of viruses that infect plants, such as tobacco mosaic virus?

  1. Polysaccharide
  2. RNA Correct answer.
  3. Protein
  4. DNA

Explanation

Tobacco mosaic virus and many plant viruses carry RNA as their genetic material, as demonstrated by the classic experiments showing that RNA alone from TMV can cause infection. Protein and polysaccharide are not genetic materials.

Question 31Genetics and Evolution (Mendelian genetics, molecular basis of inheritance, evolution)

According to the Hardy–Weinberg principle, which condition must be satisfied for allele frequencies in a population to remain constant across generations?

  1. Frequent mutation introducing new alleles
  2. Random mating with no selection, mutation, or migration Correct answer.
  3. Strong directional selection acting on a trait
  4. Significant migration between populations

Explanation

Hardy–Weinberg equilibrium requires a large population, random mating, and the absence of mutation, migration, and natural selection. Under these conditions allele and genotype frequencies stay constant from generation to generation.

Question 32Genetics and Evolution (Mendelian genetics, molecular basis of inheritance, evolution)

In a monohybrid cross, the F1 heterozygous offspring all show the dominant trait. Which term describes the allele that is not expressed in the F1 phenotype?

  1. Dominant
  2. Recessive Correct answer.
  3. Epistatic
  4. Codominant

Explanation

The recessive allele is masked in the heterozygote because the dominant allele's product determines the phenotype. It reappears in the F2 generation when two recessive alleles come together.

Question 33Genetics and Evolution (Mendelian genetics, molecular basis of inheritance, evolution)

Which enzyme unwinds the DNA double helix ahead of the replication fork during DNA replication?

  1. Helicase Correct answer.
  2. Ligase
  3. DNA polymerase
  4. Primase

Explanation

Helicase breaks the hydrogen bonds between complementary base pairs, separating the two strands so that replication can proceed. DNA polymerase then adds nucleotides to the exposed template strands.

Question 34Genetics and Evolution (Mendelian genetics, molecular basis of inheritance, evolution)

Which of the following is a homologous structure that provides evidence for common ancestry between humans and whales?

  1. Forelimbs with the same basic bone plan Correct answer.
  2. Streamlined bodies of fish and dolphins
  3. Eyes of octopuses and mammals
  4. Wings of insects and birds

Explanation

The forelimbs of humans and whales share the same underlying arrangement of bones (humerus, radius, ulna, carpals), showing descent from a common tetrapod ancestor despite different functions. Such structures are homologous.

Question 35Genetics and Evolution (Mendelian genetics, molecular basis of inheritance, evolution)

Which nitrogenous base pairs with adenine in a DNA molecule?

  1. Thymine Correct answer.
  2. Cytosine
  3. Guanine
  4. Uracil

Explanation

In DNA, adenine pairs with thymine through two hydrogen bonds, while guanine pairs with cytosine through three. Uracil replaces thymine only in RNA, not in DNA.

Question 36Genetics and Evolution (Mendelian genetics, molecular basis of inheritance, evolution)

In a cross between a heterozygous black guinea pig (Bb) and a white guinea pig (bb), what proportion of the offspring is expected to be white?

  1. One quarter
  2. One half Correct answer.
  3. All offspring
  4. Three quarters

Explanation

The Bb parent produces B and b gametes in equal proportions, while the bb parent produces only b gametes. Half the offspring are Bb (black) and half are bb (white), so one half are expected to be white.

Question 37Genetics and Evolution (Mendelian genetics, molecular basis of inheritance, evolution)

A woman with blood group AB marries a man with blood group O. Which blood groups are possible among their children?

  1. A and B only Correct answer.
  2. O only
  3. AB and O only
  4. A, B, AB and O

Explanation

The AB mother produces gametes carrying either IA or IB, while the O father produces only i gametes. The children are therefore either IAi (group A) or IBi (group B); neither AB nor O can appear because the father cannot donate IA or IB.

Question 38Genetics and Evolution (Mendelian genetics, molecular basis of inheritance, evolution)

In the lac operon of E. coli, what is the role of the repressor protein encoded by the lacI gene?

  1. It transports lactose across the cell membrane
  2. It binds the operator and blocks transcription when lactose is absent Correct answer.
  3. It cleaves lactose into glucose and galactose
  4. It activates transcription by binding the promoter when lactose is present

Explanation

In the absence of lactose, the lac repressor binds to the operator region and prevents RNA polymerase from transcribing the structural genes. When lactose is present, its inducer (allolactose) binds the repressor and releases it from the operator, allowing transcription.

Question 39Genetics and Evolution (Mendelian genetics, molecular basis of inheritance, evolution)

Which feature distinguishes the leading strand from the lagging strand during DNA replication?

  1. It is synthesised in the 3′ to 5′ direction
  2. It is synthesised continuously in the direction of fork movement Correct answer.
  3. It requires RNA primers more frequently than the lagging strand
  4. It is synthesised in short Okazaki fragments

Explanation

The leading strand is synthesised continuously because its template runs in the direction that allows DNA polymerase to move with the replication fork. The lagging strand is made discontinuously as Okazaki fragments because its template is oriented the other way.

Question 40Genetics and Evolution (Mendelian genetics, molecular basis of inheritance, evolution)

A mutation that changes a single nucleotide in a codon from GAG to GUG in the coding region of a gene would most likely be classified as which type of mutation?

  1. Silent mutation
  2. Nonsense mutation
  3. Frameshift mutation
  4. Missense mutation Correct answer.

Explanation

GAG codes for glutamic acid and GUG codes for valine, so the substitution changes one amino acid to another. Such a change is a missense mutation. It is not silent because the amino acid is altered, and not a frameshift because the reading frame stays intact.

Question 41Genetics and Evolution (Mendelian genetics, molecular basis of inheritance, evolution)

Which observation from the Meselson–Stahl experiment supported the semi-conservative model of DNA replication?

  1. After one generation, two separate heavy and light bands appeared
  2. After one generation, only a heavy band appeared
  3. After one generation in 15N, DNA formed a single hybrid band of intermediate density Correct answer.
  4. After two generations, only a heavy band appeared

Explanation

After one round of replication in 15N medium, all DNA molecules contained one old 14N strand and one new 15N strand, forming a single band of intermediate density. This hybrid band is consistent with semi-conservative replication and inconsistent with conservative or dispersive models.

Question 42Genetics and Evolution (Mendelian genetics, molecular basis of inheritance, evolution)

In a population of 1000 individuals, 360 show the recessive phenotype for a trait controlled by a single gene with two alleles. Assuming Hardy–Weinberg equilibrium, what is the frequency of the dominant allele?

  1. 0.6
  2. 0.36
  3. 0.64
  4. 0.4 Correct answer.

Explanation

The recessive phenotype frequency q² = 360/1000 = 0.36, so q = 0.6. The dominant allele frequency p = 1 − q = 0.4.

Question 43Genetics and Evolution (Mendelian genetics, molecular basis of inheritance, evolution)

Which of the following best describes the process of natural selection as proposed by Darwin?

  1. All individuals in a population reproduce at equal rates regardless of traits
  2. Acquired characteristics during an individual's lifetime are inherited by offspring
  3. Individuals with favourable heritable variations survive and reproduce more successfully Correct answer.
  4. Genetic drift randomly fixes alleles independently of their usefulness

Explanation

Darwin proposed that heritable variations giving an advantage in a particular environment lead to greater survival and reproduction, so those traits increase in frequency over generations. Acquired characteristics and random drift describe different mechanisms.

Question 44Genetics and Evolution (Mendelian genetics, molecular basis of inheritance, evolution)

Which type of RNA carries amino acids to the ribosome during translation?

  1. tRNA Correct answer.
  2. miRNA
  3. rRNA
  4. mRNA

Explanation

Transfer RNA (tRNA) has an anticodon loop that pairs with the mRNA codon and an attachment site for a specific amino acid, delivering amino acids to the growing polypeptide chain. mRNA carries the coding sequence and rRNA forms part of the ribosome.

Question 45Genetics and Evolution (Mendelian genetics, molecular basis of inheritance, evolution)

In a plant, red flower colour (R) is incompletely dominant over white (r), and heterozygotes are pink. If two pink-flowered plants are crossed, what phenotypic ratio is expected?

  1. 9 red : 3 pink : 4 white
  2. 3 red : 1 white
  3. 1 red : 2 pink : 1 white Correct answer.
  4. 1 red : 1 white

Explanation

With incomplete dominance, the heterozygote shows an intermediate phenotype. Crossing Rr × Rr gives genotypes 1 RR : 2 Rr : 1 rr, which correspond to 1 red : 2 pink : 1 white because each genotype has a distinct phenotype.

Question 46Genetics and Evolution (Mendelian genetics, molecular basis of inheritance, evolution)

Which of the following provides the strongest molecular evidence that all living organisms share a common ancestor?

  1. Presence of analogous wings in insects and birds
  2. Universality of the genetic code and ATP as an energy carrier Correct answer.
  3. Similar body shapes among unrelated aquatic animals
  4. Similar behaviour patterns in unrelated mammals

Explanation

The genetic code is virtually universal and the same energy currency (ATP) is used by all organisms, which is best explained by inheritance from a common ancestor. Analogous structures and similar behaviours can arise by convergence and do not indicate shared ancestry.

Question 47Genetics and Evolution (Mendelian genetics, molecular basis of inheritance, evolution)

In a cross involving two genes on the same chromosome, the observed frequency of recombinants is much lower than the 50% expected for independent assortment. What does this indicate?

  1. The genes assort independently on different chromosomes
  2. One gene is lethal in the homozygous condition
  3. The genes are located on the sex chromosomes
  4. The genes are linked and crossing over occurs between them Correct answer.

Explanation

Linked genes tend to be inherited together because they lie close on the same chromosome, so recombinant types appear less often than the 50% expected under independent assortment. The recombination frequency reflects the distance between the genes.

Question 48Genetics and Evolution (Mendelian genetics, molecular basis of inheritance, evolution)

Which of the following is the correct sequence of events in the central dogma of molecular biology?

  1. Protein → RNA → DNA
  2. DNA → Protein → RNA
  3. RNA → DNA → Protein
  4. DNA → RNA → Protein Correct answer.

Explanation

The central dogma states that genetic information flows from DNA to RNA through transcription and then to protein through translation. Reverse transcription (RNA to DNA) is an exception seen in retroviruses, not the general pathway.

Question 49Genetics and Evolution (Mendelian genetics, molecular basis of inheritance, evolution)

A colour-blind man marries a woman who is a carrier of the colour-blindness allele. What proportion of their sons is expected to be colour-blind?

  1. No sons
  2. One half Correct answer.
  3. All sons
  4. One quarter

Explanation

Colour blindness is X-linked recessive. The carrier mother produces X-bearing gametes with either the normal or the affected allele, while the father contributes a Y chromosome to sons. Half the sons therefore inherit the affected X and are colour-blind.

Question 50Genetics and Evolution (Mendelian genetics, molecular basis of inheritance, evolution)

In the lac operon, what happens when both lactose and glucose are present in the medium?

  1. Transcription is maximal because both the inducer and glucose are available
  2. Transcription is low because the catabolite activator protein is not bound Correct answer.
  3. Transcription is absent because lactose cannot enter the cell
  4. Transcription is maximal because the repressor is permanently bound

Explanation

Lactose removes the repressor, but high glucose lowers cAMP levels, so catabolite activator protein (CAP) does not bind the promoter and transcription stays low. Maximal lac operon expression requires lactose and low glucose.