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RBSE SS Biology study materials
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RBSE SS Biology practice questions

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Question 1Reproduction

In flowering plants, which structure develops into the fruit after fertilisation?

  1. The ovule
  2. The anther
  3. The stigma
  4. The ovary wall Correct answer.

Explanation

After double fertilisation the ovary enlarges and its wall becomes the pericarp of the fruit, while the ovules inside become seeds. The stigma and style usually wither, and the anther belongs to the male stamen and plays no part in fruit formation.

Question 2Reproduction

Which of the following is the correct sequence of events in the human male reproductive tract?

  1. Epididymis, testis, urethra, vas deferens
  2. Testis, vas deferens, epididymis, urethra
  3. Vas deferens, testis, epididymis, urethra
  4. Testis, epididymis, vas deferens, urethra Correct answer.

Explanation

Sperm are produced in the seminiferous tubules of the testis, mature and are stored in the epididymis, then travel through the vas deferens and finally the urethra during ejaculation. This order reflects the anatomical pathway of sperm from production to exit.

Question 3Reproduction

A pollen grain lands on the stigma of a flower of the same species. Which structure does the pollen tube grow through to reach the ovule?

  1. The filament
  2. The style Correct answer.
  3. The pedicel
  4. The sepal

Explanation

The pollen tube grows down through the style, which connects the stigma to the ovary, and then enters the ovule through the micropyle. The filament supports the anther, the pedicel attaches the flower to the stem, and sepals protect the bud.

Question 4Reproduction

Which hormone is responsible for the surge that triggers ovulation in the human menstrual cycle?

  1. Oxytocin
  2. Prolactin
  3. Luteinising hormone Correct answer.
  4. Progesterone

Explanation

A sharp rise in luteinising hormone (LH) around mid-cycle causes the mature Graafian follicle to rupture and release the oocyte. Progesterone dominates the luteal phase, oxytocin acts on uterine muscle during labour, and prolactin promotes milk secretion.

Question 5Reproduction

In the human female reproductive system, where does fertilisation normally occur?

  1. In the cervix
  2. In the ampulla of the fallopian tube Correct answer.
  3. In the vagina
  4. In the uterus

Explanation

Fertilisation usually takes place in the widened upper part of the oviduct, the ampulla, where sperm meet the descending oocyte. The resulting zygote then travels to the uterus for implantation.

Question 6Reproduction

Which type of asexual reproduction involves a new organism growing from a small outgrowth of the parent's body?

  1. Binary fission
  2. Budding Correct answer.
  3. Spore formation
  4. Fragmentation

Explanation

In budding, a small protrusion forms on the parent body and may detach as a new individual, as seen in Hydra and yeast. Binary fission divides the parent into two, fragmentation uses body pieces, and spore formation uses specialised reproductive cells.

Question 7Reproduction

What is the ploidy of the endosperm formed during double fertilisation in angiosperms?

  1. Tetraploid
  2. Diploid
  3. Triploid Correct answer.
  4. Haploid

Explanation

One male gamete fuses with the two polar nuclei of the central cell, giving a triploid (3n) primary endosperm nucleus. The zygote formed from the egg and the other male gamete is diploid, and gametes themselves are haploid.

Question 8Reproduction

Which structure in the human male produces testosterone?

  1. Sertoli cells of the testis
  2. The prostate gland
  3. The seminal vesicle
  4. Leydig cells of the testis Correct answer.

Explanation

Leydig (interstitial) cells lie between the seminiferous tubules and secrete testosterone under the influence of luteinising hormone. Sertoli cells support and nourish developing sperm, while the prostate and seminal vesicles add secretions to semen.

Question 9Reproduction

A gardener wants to propagate a rose plant that will be genetically identical to the parent. Which method should be chosen?

  1. Stem cutting Correct answer.
  2. Seed sowing after selfing
  3. Cross-pollination
  4. Raising seedlings from hybrid seed

Explanation

Vegetative propagation by stem cutting produces clones because only mitotic divisions occur in the growing tissues. Sexual methods such as pollination and seed sowing involve meiosis and recombination, so the offspring vary and need not match the parent.

Question 10Reproduction

A woman's corpus luteum fails to develop after ovulation. Which immediate consequence is most likely?

  1. The oocyte fails to complete meiosis II
  2. Progesterone falls and the endometrium is shed Correct answer.
  3. Follicle-stimulating hormone stops being secreted by the pituitary
  4. Oestrogen rises and blocks the pituitary completely

Explanation

The corpus luteum secretes progesterone, which maintains the thickened endometrium. Without it, progesterone levels fall, the endometrium breaks down, and menstruation follows because the hormonal support for pregnancy is lost.

Question 11Reproduction

Which statement best explains why cross-pollination generally increases genetic variation in a plant population?

  1. It brings together gametes from two different plants, so new allele combinations arise Correct answer.
  2. It produces seeds without meiosis
  3. It avoids the need for any pollinating agent
  4. It guarantees that every seed will germinate successfully

Explanation

Cross-pollination fuses gametes from genetically different parents, and because each gamete arises through meiosis, the offspring receive novel combinations of alleles. Self-pollination restricts this mixing, and pollination never bypasses meiosis.

Question 12Reproduction

In a species where the male is heterogametic (XY), which statement about gamete sex chromosomes is correct?

  1. All sperm carry X, so the mother determines the sex
  2. Half the sperm carry X and half carry Y, so the father determines the sex of the offspring Correct answer.
  3. The egg carries either X or Y, so the mother determines the sex
  4. All sperm carry Y, so the father determines the sex

Explanation

During meiosis the X and Y chromosomes separate, so a male produces equal numbers of X-bearing and Y-bearing sperm. The egg always carries an X, so the sperm's chromosome determines whether the zygote is XX or XY.

Question 13Reproduction

Which of the following correctly describes the role of the placenta?

  1. It stores the embryo until birth without any exchange
  2. It allows exchange of nutrients, gases and wastes between maternal and fetal blood without mixing them Correct answer.
  3. It produces sperm and oestrogen for the fetus
  4. It mixes maternal and fetal blood so that antibodies are transferred directly

Explanation

The placenta brings fetal and maternal circulations close together so that materials diffuse across, but the two bloods remain separate. It also secretes hormones such as hCG and progesterone that support pregnancy.

Question 14Reproduction

A student observes that a Hydra reproduces by budding while a Planaria reproduces by fragmentation. Which feature distinguishes these two processes?

  1. In budding the new individual arises from an outgrowth of the parent, whereas in fragmentation it arises from a separated body piece Correct answer.
  2. In budding meiosis occurs, whereas in fragmentation it does not
  3. In budding the offspring are genetically different, whereas in fragmentation they are identical
  4. In fragmentation gametes fuse, whereas in budding they do not

Explanation

Budding produces a new individual from a small outgrowth that may remain attached, while fragmentation depends on a broken piece of the body regenerating into a whole organism. Both are asexual and therefore produce genetically identical offspring.

Question 15Reproduction

Which event marks the completion of the first meiotic division in a primary oocyte?

  1. Release of the first polar body Correct answer.
  2. Fusion of the sperm with the egg
  3. Formation of the zygote
  4. Implantation of the blastocyst

Explanation

Meiosis I in the primary oocyte produces a large secondary oocyte and a small first polar body, which is extruded. The secondary oocyte then arrests at metaphase II until fertilisation triggers completion of meiosis II.

Question 16Reproduction

In a flowering plant, the megaspore mother cell undergoes meiosis. What is the immediate product of this division?

  1. Four diploid polar nuclei
  2. Four haploid megaspores Correct answer.
  3. One diploid embryo sac
  4. Two haploid pollen grains

Explanation

The diploid megaspore mother cell undergoes meiosis to give four haploid megaspores, of which usually only one survives to form the embryo sac. The embryo sac itself is haploid and contains polar nuclei formed later by mitosis.

Question 17Reproduction

Which contraceptive method works primarily by preventing the release of an ovum from the ovary?

  1. Condoms
  2. Diaphragms
  3. Combined oral contraceptive pills Correct answer.
  4. Intrauterine devices

Explanation

Combined pills contain oestrogen and progestogen that suppress FSH and LH release, so follicular development and ovulation are inhibited. Barrier methods such as condoms and diaphragms physically stop sperm from meeting the egg.

Question 18Reproduction

A plant produces flowers that lack brightly coloured petals but have long feathery stigmas and large numbers of light pollen grains. Which pollination strategy does this indicate?

  1. Water pollination
  2. Insect pollination
  3. Self-pollination within a closed bud
  4. Wind pollination Correct answer.

Explanation

Feathery stigmas catch airborne pollen, and abundant light pollen is easily carried by wind, while the absence of showy petals reflects that no animal pollinator is attracted. Insect-pollinated flowers typically have bright petals and sticky pollen.

Question 19Reproduction

Which sequence correctly describes the development of a human embryo from fertilisation to implantation?

  1. Zygote, blastocyst, morula, implantation
  2. Blastocyst, zygote, morula, implantation
  3. Zygote, morula, blastocyst, implantation Correct answer.
  4. Morula, zygote, blastocyst, implantation

Explanation

The zygote undergoes cleavage to form a solid morula, which then becomes a hollow blastocyst with an inner cell mass. The blastocyst hatches from the zona pellucida and implants in the endometrium.

Question 20Reproduction

Which statement correctly compares spermatogenesis and oogenesis in humans?

  1. Spermatogenesis occurs only before birth, whereas oogenesis continues throughout life
  2. Spermatogenesis produces four functional sperm per meiosis, whereas oogenesis produces one functional ovum and polar bodies Correct answer.
  3. Both processes produce four functional gametes from each meiosis
  4. Spermatogenesis produces one functional sperm, whereas oogenesis produces four functional ova

Explanation

In males, cytoplasmic division during meiosis gives four viable sperm from each primary spermatocyte. In females, the cytoplasm is retained by one cell, so meiosis yields one large ovum and up to three polar bodies that degenerate.

Question 21Reproduction

A flower is described as having a superior ovary. Which floral feature is most consistent with this condition?

  1. The ovary develops into an accessory fruit
  2. The ovary lies embedded in the receptacle below the other floral parts
  3. The sepals, petals and stamens are attached below the ovary Correct answer.
  4. The ovary is enclosed by a fused hypanthium

Explanation

In a superior ovary the floral parts are inserted on the receptacle beneath the ovary, as in hypogynous flowers. An inferior ovary lies below the attachment of sepals, petals and stamens and is often associated with epigynous flowers.

Question 22Reproduction

In the human menstrual cycle, which hormonal change directly causes the endometrium to thicken during the follicular phase?

  1. Rising prolactin from the anterior pituitary
  2. A surge of luteinising hormone at mid-cycle
  3. Rising oestrogen secreted by the developing follicle Correct answer.
  4. Falling progesterone from the corpus luteum

Explanation

Oestrogen from the growing follicle stimulates proliferation of the endometrium during the follicular phase. Progesterone acts later, after ovulation, to make the endometrium secretory and receptive to implantation.

Question 23Reproduction

Which observation would best support the conclusion that a particular plant is wind-pollinated rather than insect-pollinated?

  1. The flowers have bright ultraviolet patterns visible to insects
  2. The flowers open only at night and secrete nectar
  3. The flowers have large scented petals and produce sticky pollen
  4. The flowers are small, dull-coloured, and produce large quantities of dry, light pollen Correct answer.

Explanation

Wind-pollinated flowers are typically inconspicuous and unscented, with abundant light dry pollen and exposed stigmas to catch airborne grains. Showy petals, scent, nectar and sticky pollen are adaptations that attract and attach pollen to animal visitors.

Question 24Reproduction

A mutation prevents the formation of the synergids in an angiosperm embryo sac. Which process is most directly affected?

  1. Guidance of the pollen tube to the egg and entry of the sperm into the embryo sac Correct answer.
  2. Development of the fruit from the ovary wall
  3. Formation of the seed coat from the integuments
  4. Formation of the endosperm after fertilisation

Explanation

Synergids lie at the micropylar end of the embryo sac and are involved in guiding the pollen tube and facilitating sperm entry during double fertilisation. Endosperm formation depends on the central cell's polar nuclei, and the seed coat and fruit arise from maternal tissues.

Question 25Reproduction

Which statement correctly explains why the corpus luteum is essential for the early weeks of pregnancy?

  1. It produces oestrogen that triggers ovulation again
  2. It secretes oxytocin that initiates labour
  3. It secretes hCG that directly stimulates the pituitary to release FSH
  4. It secretes progesterone that maintains the endometrium until the placenta takes over Correct answer.

Explanation

The corpus luteum secretes progesterone, which keeps the endometrium thick and prevents its breakdown during early pregnancy. Human chorionic gonadotrophin from the embryo maintains the corpus luteum until the placenta can produce sufficient progesterone itself.

Question 26Reproduction

In humans, which process directly produces the haploid cells that fuse during fertilisation?

  1. Mitosis in the zygote
  2. Budding in the ovary
  3. Meiosis in the gonads Correct answer.
  4. Binary fission in the uterus

Explanation

Gametes are formed by meiosis, a reduction division that halves the chromosome number so each gamete carries a single set of chromosomes. Their fusion at fertilisation restores the diploid number in the zygote. Mitosis and the other listed processes do not generate haploid gametes in humans.

Question 27Reproduction

A pollen grain lands on the stigma of a compatible flower and germinates. Which structure does the pollen tube ultimately deliver the male gametes to?

  1. The antipodal cells of the style
  2. The generative cell of the anther
  3. The nucellus of the integument
  4. The embryo sac within the ovule Correct answer.

Explanation

After germination the pollen tube grows down the style and enters the ovule through the micropyle, releasing male gametes into the embryo sac. There one fuses with the egg and another with the polar nuclei during double fertilisation. The style and anther are not the final destination of the tube.

Question 28Reproduction

A farmer wants a large number of uniform, disease-free banana plants quickly from a single superior parent. Which approach best meets these requirements?

  1. Cross-pollinating the parent with a wild variety
  2. Raising new plants from pollen grains in a nursery
  3. Growing plants from the seeds of the parent
  4. Propagating the parent vegetatively by tissue culture Correct answer.

Explanation

Tissue culture is a form of vegetative propagation in which many genetically identical plantlets are produced rapidly from the parent's somatic tissue. Because the offspring are clones of the selected parent, uniformity and desirable traits are preserved. Seed and pollen-based methods involve meiosis and recombination, so offspring vary.

Question 29Reproduction

A woman begins taking a combined oral contraceptive pill containing oestrogen and progestogen. Which hormonal effect most directly prevents ovulation?

  1. Rising FSH and LH stimulate follicle maturation
  2. Oestrogen triggers the mid-cycle LH surge
  3. Negative feedback suppresses FSH and LH release Correct answer.
  4. Progesterone directly degenerates the mature follicle

Explanation

The combined pill maintains steady levels of oestrogen and progestogen, which exert negative feedback on the hypothalamus and anterior pituitary. This suppresses FSH and LH secretion, so no dominant follicle matures and the LH surge that triggers ovulation does not occur. The pill therefore prevents ovulation through hormonal suppression rather than by stimulating the gonads.

Question 30Reproduction

In a human female, the secondary oocyte is released at ovulation while still arrested in a particular stage. Which stage is this?

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

Explanation

The secondary oocyte is released at ovulation arrested at metaphase of meiosis II, and it completes the division only if a sperm penetrates it. Meiosis I is already finished at ovulation, so prophase I describes the primary oocyte, not the released cell. This timing ensures the egg completes maturation only after fertilisation.

Question 31Reproduction

A student compares a wind-pollinated grass with an insect-pollinated flower. Which pair of features most reliably distinguishes the grass?

  1. Bright bracts and nectar-rich nectaries
  2. Exposed feathery stigmas and abundant light pollen Correct answer.
  3. Large sticky pollen and scented petals
  4. Heavy pollen and enclosed tubular corolla

Explanation

Wind-pollinated flowers rely on chance, so they produce large quantities of small, light pollen and expose feathery stigmas that trap airborne grains. They typically lack showy petals, scent and nectar because they do not need to attract animals. Insect-pollinated flowers instead invest in attractants and sticky pollen.

Question 32Reproduction

In a species where the female is heterogametic (ZW), a male and a female are crossed. Which statement about the sex of the offspring is correct?

  1. Sex is determined solely by environmental temperature
  2. The father's gamete determines the sex of each offspring
  3. The mother's gamete determines the sex of each offspring Correct answer.
  4. All offspring inherit a Z from the mother and are male

Explanation

In ZW systems the female has two different sex chromosomes and therefore produces two kinds of gametes, one carrying Z and one carrying W. The male is ZZ and contributes only Z-bearing sperm, so the mother's gamete determines whether the offspring is male (ZZ) or female (ZW). This is the mirror image of the XY situation in humans.

Question 33Genetics and Evolution

In Mendel's monohybrid cross between true-breeding tall (TT) and true-breeding dwarf (tt) pea plants, what phenotype and genotype ratio appears in the F2 generation?

  1. 9 tall : 3 dwarf phenotype, with genotype ratio 1 TT : 2 Tt : 1 tt
  2. All tall phenotype, with genotype ratio 1 TT : 1 Tt
  3. 1 tall : 1 dwarf phenotype, with genotype ratio 1 Tt : 1 tt
  4. 3 tall : 1 dwarf phenotype, with genotype ratio 1 TT : 2 Tt : 1 tt Correct answer.

Explanation

The F1 heterozygotes (Tt) are all tall because T is dominant. Selfing the F1 gives F2 offspring in a 3:1 phenotypic ratio of tall to dwarf, which corresponds to the genotypic ratio 1 TT : 2 Tt : 1 tt.

Question 34Genetics and Evolution

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

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

Explanation

The AB parent transmits either the IA or the IB allele, while the O parent transmits only the i allele. Children therefore have genotype IAi (group A) or IBi (group B), so only groups A and B can appear.

Question 35Genetics and Evolution

Which observation from a dihybrid cross most directly supports the law of independent assortment?

  1. A test cross of a heterozygote gives a 1:1 ratio for a single trait
  2. Reciprocal crosses produce identical results regardless of which parent supplies which trait
  3. New phenotypic combinations such as round-green and wrinkled-yellow appear in the F2 generation Correct answer.
  4. The F1 generation shows only the dominant phenotype for both traits

Explanation

Independent assortment predicts that alleles of different genes segregate independently, generating recombinant phenotypes not seen in the parents. The appearance of round-green and wrinkled-yellow F2 seeds in a 9:3:3:1 pattern is the classic evidence.

Question 36Genetics and Evolution

In a dihybrid cross between two heterozygotes (RrYy × RrYy) with independent assortment, what proportion of offspring is expected to be homozygous recessive for both traits?

  1. 9/16
  2. 1/16 Correct answer.
  3. 1/4
  4. 3/16

Explanation

Each parent produces the ry gamete with probability 1/4, so the double recessive offspring (rryy) occurs with probability 1/4 × 1/4 = 1/16. This matches the smallest class of the 9:3:3:1 ratio.

Question 37Genetics and Evolution

What is the chromosomal basis of incomplete dominance?

  1. The heterozygote produces an intermediate phenotype because one dominant allele does not fully mask the other Correct answer.
  2. Both alleles are expressed equally and separately in the same tissue
  3. The two alleles always segregate to the same gamete
  4. One allele is completely absent from the heterozygote's genome

Explanation

In incomplete dominance the dominant allele's product is insufficient to fully mask the recessive allele, so the heterozygote shows a phenotype between the two homozygotes. Neither allele is lost; they simply interact to give an intermediate expression.

Question 38Genetics and Evolution

A man with haemophilia (X-linked recessive) marries a homozygous unaffected woman. What is expected for their children?

  1. All children are affected
  2. Half the sons are affected and half the daughters are affected
  3. All daughters are affected and all sons are carriers
  4. All daughters are carriers and all sons are unaffected Correct answer.

Explanation

The affected father contributes his X chromosome (carrying the haemophilia allele) to every daughter, making them carriers, and his Y chromosome to every son. Sons receive a normal X from the mother, so no son is affected.

Question 39Genetics and Evolution

Why do X-linked recessive disorders appear more frequently in males than in females?

  1. Females have no copies of the affected gene
  2. The recessive allele is located on the Y chromosome in males
  3. Males inherit two X chromosomes, doubling their chance of receiving the allele
  4. Males are hemizygous, so a single recessive allele on their only X chromosome is expressed Correct answer.

Explanation

Males carry only one X chromosome, so a recessive allele on that chromosome has no homologous partner to mask it. Females need two copies of the allele to be affected, which is statistically less likely.

Question 40Genetics and Evolution

In a pedigree, a trait appears in every generation, affects about half the offspring of an affected parent, and affects males and females equally. Which mode of inheritance is most consistent with this pattern?

  1. Y-linked
  2. X-linked recessive
  3. Autosomal dominant Correct answer.
  4. Autosomal recessive

Explanation

Appearance in every generation with roughly equal sex distribution and transmission from an affected parent to about half the children fits autosomal dominant inheritance. Each affected heterozygote passes the allele to half its offspring.

Question 41Genetics and Evolution

A human somatic cell in G1 phase contains 46 chromosomes. What is the DNA content and chromosome number after S phase is complete, before mitosis begins?

  1. 23 chromosomes, each with two sister chromatids
  2. 92 chromosomes, each with one chromatid
  3. 46 chromosomes, each with one chromatid
  4. 46 chromosomes, each with two sister chromatids Correct answer.

Explanation

DNA replication in S phase duplicates each chromosome into two sister chromatids but does not change the chromosome count. The cell therefore still has 46 chromosomes, now each consisting of two chromatids.

Question 42Genetics and Evolution

Which event during meiosis is the principal source of genetic recombination between homologous chromosomes?

  1. Condensation of chromatin in prophase II
  2. Separation of sister chromatids in anaphase II
  3. Formation of the spindle apparatus in metaphase I
  4. Crossing over between non-sister chromatids at chiasmata in prophase I Correct answer.

Explanation

Crossing over exchanges segments between non-sister chromatids of homologous chromosomes at chiasmata during prophase I. This creates new allele combinations on the recombinant chromatids.

Question 43Genetics and Evolution

In a test cross, an organism showing the dominant phenotype is crossed with a homozygous recessive individual. What is the purpose of this cross?

  1. To determine whether the dominant-phenotype individual is homozygous or heterozygous Correct answer.
  2. To convert recessive alleles into dominant alleles
  3. To increase the number of dominant offspring
  4. To produce pure-breeding lines in one generation

Explanation

A test cross reveals the unknown genotype because the recessive parent contributes only recessive alleles. If any recessive offspring appear, the tested individual must be heterozygous; if none appear, it is likely homozygous dominant.

Question 44Genetics and Evolution

In snapdragon plants, red (RR) crossed with white (rr) gives pink (Rr) flowers. What phenotypic ratio results from crossing two pink-flowered plants?

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

Explanation

Because neither allele is completely dominant, each genotype has a distinct phenotype. The cross Rr × Rr yields 1 RR (red) : 2 Rr (pink) : 1 rr (white).

Question 45Genetics and Evolution

Which statement about the law of segregation is correct?

  1. Alleles of different genes always stay together in the same gamete
  2. Both alleles of a gene enter the same gamete
  3. Dominant alleles segregate while recessive alleles do not
  4. The two alleles of a gene separate from each other during gamete formation Correct answer.

Explanation

Segregation states that the paired alleles of a gene separate during meiosis so that each gamete receives only one allele. This explains why a heterozygote produces two kinds of gametes in equal numbers.

Question 46Genetics and Evolution

A cross between a heterozygous tall pea plant (Tt) and a dwarf plant (tt) produces 200 offspring. Approximately how many are expected to be dwarf?

  1. 200
  2. 50
  3. 150
  4. 100 Correct answer.

Explanation

The cross Tt × tt gives a 1:1 ratio of tall (Tt) to dwarf (tt) offspring. Half of 200 offspring, or about 100, are expected to be dwarf.

Question 47Genetics and Evolution

Which of these is a correct description of a polygenic trait?

  1. A trait controlled by a single gene with two alleles showing complete dominance
  2. A trait whose alleles are located on the Y chromosome
  3. A trait controlled by many genes, each contributing a small additive effect to the phenotype Correct answer.
  4. A trait determined only by environmental factors

Explanation

Polygenic traits such as human height and skin colour are governed by multiple genes whose alleles add up to produce continuous variation. The resulting phenotypes usually form a bell-shaped distribution.

Question 48Genetics and Evolution

In humans, the allele for brown eyes (B) is dominant over blue eyes (b). A brown-eyed man whose mother had blue eyes marries a blue-eyed woman. What is the probability that their first child will have blue eyes?

  1. 1/2 Correct answer.
  2. 0
  3. 3/4
  4. 1/4

Explanation

The man must be heterozygous (Bb) because his mother was bb. Crossing Bb with bb gives a 1:1 ratio of brown to blue, so the chance of a blue-eyed child is 1/2.

Question 49Genetics and Evolution

Which of the following best describes a mutation that can be inherited by offspring?

  1. A change in the amino acid sequence of a protein caused by enzyme activity
  2. A temporary change in gene expression without any DNA alteration
  3. A change in the DNA of a skin cell caused by ultraviolet light
  4. A change in the DNA sequence of germ-line cells Correct answer.

Explanation

Only mutations in germ-line cells, which give rise to gametes, can be passed to the next generation. Somatic mutations affect only the individual in which they occur.

Question 50Genetics and Evolution

A frameshift mutation occurs when a single nucleotide is inserted into a coding sequence. What is the most likely consequence?

  1. No change occurs because the genetic code is degenerate
  2. The reading frame is restored after three nucleotides
  3. All codons downstream of the insertion are read differently, usually producing a non-functional protein Correct answer.
  4. Only the codon at the insertion site is altered

Explanation

Inserting a nucleotide shifts the reading frame for every codon after the mutation site. The resulting amino acid sequence is completely different and often ends in a premature stop codon.