I85PREP
⌘ K
Pancyprian Biology study materials
Pancyprian Biology study resources

Pancyprian Biology practice questions

One question at a time. Build your Pancyprian Biology understanding.

First 50 of 190 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.

Continue in the practice tool above to load more questions, 50 at a time.

Question 1Biological inquiry and interpretation of evidence

A researcher predicts that tomato plants given a nitrogen-enriched fertilizer will produce more fruit than plants given a standard fertilizer. In this study, the amount of fruit produced is best described as which of the following?

  1. The hypothesis
  2. A controlled variable
  3. The dependent variable Correct answer.
  4. The independent variable

Explanation

The dependent variable is the measured outcome that responds to the manipulation, which here is fruit yield. The fertilizer type is the factor the researcher deliberately changes, so it is the independent variable rather than the measured result.

Question 2Biological inquiry and interpretation of evidence

A student measures the mass of the same sample five times and obtains nearly identical values, but the balance was never zeroed and reads 2.0 g too high. How should these measurements be described?

  1. Both accurate and precise
  2. Precise but not accurate Correct answer.
  3. Accurate but not precise
  4. Neither accurate nor precise

Explanation

Precision refers to how closely repeated measurements agree with one another, while accuracy refers to how close they are to the true value. Because the readings cluster tightly but are systematically offset by the unzeroed balance, they are precise but inaccurate.

Question 3Biological inquiry and interpretation of evidence

Which of the following best distinguishes a scientific hypothesis from a scientific theory?

  1. A hypothesis is a testable proposed explanation, while a theory is a well-supported explanatory framework built from extensive evidence Correct answer.
  2. A hypothesis is always correct once tested, while a theory remains an untested guess
  3. A hypothesis is a broad framework, while a theory is a single testable prediction
  4. A hypothesis applies only to biology, while a theory applies only to physics

Explanation

In science, a hypothesis is a testable proposed explanation for a specific observation, whereas a theory is a broad, well-substantiated explanation supported by many lines of evidence. The common usage of theory as a mere guess is incorrect in scientific contexts.

Question 4Biological inquiry and interpretation of evidence

A scientist repeats an experiment several times and obtains consistent results. Which conclusion is most justified?

  1. The findings are reliable and reproducible under the tested conditions Correct answer.
  2. The results now apply to all organisms everywhere
  3. The hypothesis has been proven true beyond any doubt
  4. The experiment has no remaining sources of error

Explanation

Reproducible results indicate reliability, meaning the procedure yields consistent outcomes under the tested conditions. Science does not establish absolute proof, and replication does not eliminate error or guarantee universal applicability.

Question 5Biological inquiry and interpretation of evidence

A graph plots plant height on the y-axis against days of growth on the x-axis. Which statement correctly identifies the placement of these variables?

  1. Days of growth is the independent variable on the x-axis, and height is the dependent variable on the y-axis Correct answer.
  2. Both variables are dependent and should share the x-axis
  3. Days of growth is the dependent variable because it is measured over time
  4. Height is the independent variable on the y-axis, and days of growth is the dependent variable on the x-axis

Explanation

By convention, the independent variable is placed on the x-axis and the dependent variable on the y-axis. Height responds to elapsed time, so time is independent and height is dependent.

Question 6Biological inquiry and interpretation of evidence

A student notices that mold grows on bread left in a warm, humid place but not on bread stored in a dry, cool place. Which of the following is the most appropriate next step in the scientific process?

  1. Formulate a testable hypothesis and design a controlled experiment to test it Correct answer.
  2. Conclude immediately that warmth and moisture cause mold growth
  3. Publish the observation as a confirmed scientific law
  4. Discard the observation because it was not made in a laboratory

Explanation

An observation generates questions that should be framed as a testable hypothesis and examined through a controlled experiment. Reaching a firm causal conclusion from a single uncontrolled observation is premature.

Question 7Biochemistry

Which property of water is most directly responsible for its ability to moderate temperature in living organisms and large bodies of water?

  1. Its low specific heat
  2. Its inability to form hydrogen bonds
  3. Its nonpolar covalent bonds
  4. Its high specific heat Correct answer.

Explanation

Water has a high specific heat because hydrogen bonds must absorb or release substantial energy before water molecules change temperature. This allows water and water-rich organisms to resist large temperature swings, helping maintain homeostasis.

Question 8Cell structure, membranes and division

Which structure is found in a typical plant cell but NOT in a typical animal cell?

  1. Mitochondrion
  2. Nucleus
  3. Ribosome
  4. Cell wall made of cellulose Correct answer.

Explanation

Plant cells have a rigid cell wall composed primarily of cellulose that surrounds the plasma membrane, providing structural support. Animal cells lack a cell wall, relying on the cytoskeleton and extracellular matrix instead.

Question 9Genetics, inheritance and molecular information

Meiosis differs from mitosis in that meiosis produces

  1. Two genetically identical diploid cells
  2. One diploid cell with double the chromosomes
  3. Two haploid cells identical to the parent
  4. Four genetically varied haploid cells Correct answer.

Explanation

Meiosis consists of two divisions that produce four haploid gametes, each with half the chromosome number of the parent. Crossing over and independent assortment generate genetic variation, distinguishing meiosis from the identical-diploid products of mitosis.

Question 10Metabolism

An enzyme lowers the activation energy of a reaction. Which statement best describes how this affects the reaction?

  1. It increases the reaction rate without being consumed in the reaction Correct answer.
  2. It changes the overall free-energy difference between reactants and products
  3. It supplies the energy needed to make an endergonic reaction exergonic
  4. It permanently binds to the product to stop the reaction

Explanation

Enzymes are biological catalysts that lower activation energy, speeding up reactions without being consumed. They do not change the net free-energy difference (delta G) between reactants and products; they only make the reaction reach equilibrium faster.

Question 11Physiology

Which feature allows a steroid hormone to pass directly through the plasma membrane?

  1. Its lipid (hydrophobic) nature lets it dissolve through the phospholipid bilayer Correct answer.
  2. Its large size lets it push proteins aside
  3. Its negative charge attracts it to the membrane interior
  4. Its attachment to a carbohydrate tag opens a channel

Explanation

Steroid hormones are lipid-soluble (hydrophobic), so they can dissolve through the hydrophobic interior of the phospholipid bilayer without a transport protein. Once inside, they typically bind intracellular receptors that act on the DNA to regulate gene expression.

Question 12Ecology

In an energy pyramid, only about 10 percent of the energy at one trophic level is transferred to the next. Most of the remaining energy is

  1. Converted directly into new biomass at the next level
  2. Lost as heat, largely through cellular respiration and metabolic processes Correct answer.
  3. Stored permanently in the soil
  4. Recycled back to producers as light energy

Explanation

At each trophic level, organisms use most of the energy they consume for metabolism and lose much of it as heat through cellular respiration. Only about 10 percent is stored as biomass available to the next level, which limits food chain length.

Question 13Evolution

Which of the following is a necessary condition for natural selection to occur in a population?

  1. All individuals are genetically identical
  2. Heritable variation exists and affects survival or reproduction Correct answer.
  3. The environment never changes
  4. Every individual produces the same number of offspring

Explanation

Natural selection requires heritable variation among individuals and differences in reproductive success linked to that variation. Individuals with advantageous heritable traits leave more offspring, shifting the population's traits over generations.

Question 14Cell structure, membranes and division

Which organelle is the main site of aerobic respiration in a eukaryotic cell?

  1. Chloroplast
  2. Ribosome
  3. Mitochondrion Correct answer.
  4. Golgi apparatus

Explanation

The mitochondrion is often called the powerhouse of the cell because the Krebs cycle and oxidative phosphorylation take place there, producing most of the cell's ATP. Its folded inner membrane (cristae) provides a large surface for the respiratory chain.

Question 15Cell structure, membranes and division

Which feature is found in prokaryotic cells but NOT in eukaryotic cells?

  1. A cell membrane
  2. Ribosomes
  3. Circular DNA lying free in the cytoplasm without a nucleus Correct answer.
  4. Cytoplasm

Explanation

Prokaryotes, such as bacteria, lack a membrane-bound nucleus; their genetic material is a circular DNA molecule in a region called the nucleoid. Eukaryotic cells enclose their linear chromosomes inside a nuclear envelope. Both cell types share a membrane, cytoplasm and ribosomes.

Question 16Cell structure, membranes and division

The rough endoplasmic reticulum appears 'rough' under the electron microscope because it is studded with:

  1. Lysosomes
  2. Ribosomes that synthesise proteins for export Correct answer.
  3. Vesicles containing digestive enzymes
  4. Chlorophyll pigments

Explanation

The rough endoplasmic reticulum is covered with bound ribosomes, which synthesise proteins destined for secretion, membrane insertion or lysosomes. These proteins enter the ER lumen for folding and are then transported to the Golgi apparatus.

Question 17Cell structure, membranes and division

Which structure is present in a plant leaf cell but absent from an animal cell?

  1. Mitochondrion
  2. Cell membrane
  3. Cellulose cell wall Correct answer.
  4. Nucleus

Explanation

Plant cells are surrounded by a rigid cellulose cell wall outside the cell membrane, which provides support and limits water uptake by osmosis. Animal cells have only a flexible cell membrane. Both cell types contain mitochondria and nuclei.

Question 18Cell structure, membranes and division

The key difference between active transport and facilitated diffusion across a cell membrane is that active transport:

  1. Requires ATP and can move substances against their concentration gradient Correct answer.
  2. Always moves substances down their concentration gradient
  3. Does not require any membrane proteins
  4. Only transports water molecules

Explanation

Active transport uses energy from ATP hydrolysis to pump substances from a region of lower to higher concentration, against the gradient, via carrier proteins such as the sodium-potassium pump. Facilitated diffusion also uses proteins but moves substances down their gradient without ATP.

Question 19Cell structure, membranes and division

A red blood cell is placed in distilled water (a hypotonic solution). What will happen to the cell?

  1. It will shrink because water leaves by osmosis
  2. It will swell and may burst because water enters by osmosis Correct answer.
  3. It will stay the same size because the membrane is impermeable to water
  4. It will pump water out by active transport and stay unchanged

Explanation

Distilled water has a higher water potential than the cell's cytoplasm, so water enters the cell by osmosis. Red blood cells have no cell wall, so the inflow of water causes them to swell and eventually haemolyse (burst).

Question 20Cell structure, membranes and division

Identical potato cylinders were weighed, placed in sucrose solutions of different concentrations for one hour, and reweighed. Results: 0.0 M sucrose +8% mass; 0.2 M +4%; 0.4 M -1%; 0.6 M -7%. The sucrose concentration closest to the water potential of the potato cells is approximately:

  1. 0.0 M
  2. 0.2 M
  3. 0.4 M Correct answer.
  4. 0.6 M

Explanation

When the external solution has the same water potential as the cells, there is no net water movement and mass stays constant. The mass change crosses zero between 0.2 M (+4%) and 0.4 M (-1%), so the isotonic point lies closest to 0.4 M (just under it).

Question 21Cell structure, membranes and division

Enzymes are best described as:

  1. Carbohydrates that provide energy for reactions
  2. Biological catalysts, usually proteins, that speed up reactions without being used up Correct answer.
  3. Hormones that carry messages between cells
  4. Lipids that form the cell membrane

Explanation

Enzymes are biological catalysts; almost all are proteins. They lower the activation energy of metabolic reactions, greatly increasing reaction rate, and emerge unchanged so they can be used repeatedly.

Question 22Cell structure, membranes and division

Heating an enzyme well above its optimum temperature permanently reduces its activity because:

  1. The enzyme molecules are completely digested by the substrate
  2. The enzyme's active site changes shape as the protein denatures Correct answer.
  3. The substrate molecules are destroyed
  4. The enzyme molecules freeze into fixed positions

Explanation

High temperatures break the bonds maintaining the enzyme's tertiary structure. The active site loses its specific shape so the substrate can no longer bind; this denaturation is usually irreversible.

Question 23Cell structure, membranes and division

In the induced-fit model of enzyme action, the active site:

  1. Is a rigid shape that never changes
  2. Changes shape slightly as the substrate binds, improving the fit Correct answer.
  3. Is identical in all enzymes
  4. Binds any substrate with equal strength

Explanation

The induced-fit model proposes that the active site is flexible and moulds itself around the substrate as it binds, forming the enzyme-substrate complex and stressing the bonds to be broken. This refines the older rigid lock-and-key model while retaining enzyme specificity.

Question 24Cell structure, membranes and division

A graph of enzyme activity against pH shows a sharp peak at pH 2 and almost no activity above pH 5. This enzyme most likely works in the:

  1. Small intestine, where conditions are alkaline
  2. Stomach, where conditions are strongly acidic Correct answer.
  3. Blood plasma, where pH is near neutral
  4. Mouth, where pH is around neutral

Explanation

An optimum at pH 2 matches the strongly acidic environment of the stomach, where hydrochloric acid maintains a low pH and the protease pepsin works. Enzymes of the small intestine, blood and mouth have optima near neutral or slightly alkaline pH.

Question 25Cell structure, membranes and division

A competitive inhibitor reduces enzyme activity by:

  1. Permanently destroying the enzyme's structure
  2. Binding to the active site and blocking substrate access, an effect reduced by adding more substrate Correct answer.
  3. Binding elsewhere on the enzyme so that adding more substrate has no effect
  4. Removing the products of the reaction

Explanation

A competitive inhibitor has a shape similar to the substrate and occupies the active site, preventing substrate binding. Because inhibitor and substrate compete, raising the substrate concentration increases the chance of substrate binding and reduces the inhibition.

Question 26Cell structure, membranes and division

In photosynthesis, the light-dependent reactions take place in the:

  1. Stroma of the chloroplast
  2. Thylakoid membranes of the chloroplast Correct answer.
  3. Matrix of the mitochondrion
  4. Cytoplasm

Explanation

The light-dependent reactions occur on the thylakoid membranes, where chlorophyll absorbs light energy to split water (photolysis) and generate ATP and NADPH. The light-independent reactions (Calvin cycle) occur in the stroma.

Question 27Cell structure, membranes and division

Which products of the light-dependent reactions of photosynthesis are required for the Calvin cycle?

  1. Oxygen and glucose
  2. ATP and NADPH Correct answer.
  3. Carbon dioxide and water
  4. ADP and NADP+

Explanation

The light reactions produce ATP and reduced NADP (NADPH), which supply the energy and reducing power to fix carbon dioxide into carbohydrate in the Calvin cycle. Oxygen is released as a by-product and ADP/NADP+ are recycled back to the light reactions.

Question 28Cell structure, membranes and division

During the Calvin cycle, carbon dioxide is fixed by combining with a five-carbon compound in the:

  1. Thylakoid membrane
  2. Stroma Correct answer.
  3. Intermembrane space of the mitochondrion
  4. Cell wall

Explanation

Carbon dioxide fixation occurs in the stroma of the chloroplast, where CO2 combines with the five-carbon compound RuBP, catalysed by the enzyme rubisco. The resulting compounds are reduced using ATP and NADPH from the light reactions to form carbohydrates.

Question 29Cell structure, membranes and division

In an experiment, the rate of photosynthesis was measured at increasing light intensities at two CO2 concentrations. At 0.04% CO2 the rate rose then levelled off at moderate light; at 0.4% CO2 the rate kept rising to a higher plateau. The most reasonable conclusion is that:

  1. Light intensity was the only limiting factor throughout
  2. At high light intensity and low CO2, carbon dioxide became the limiting factor Correct answer.
  3. CO2 concentration never limits photosynthesis
  4. Temperature must have been the limiting factor at all points

Explanation

The plateau at low CO2 despite increasing light shows that another factor limits the rate; raising CO2 lifted the plateau, identifying CO2 as the limiting factor there. This illustrates the principle of limiting factors: the rate is set by whichever factor is in shortest supply.

Question 30Cell structure, membranes and division

The correct overall word equation for aerobic respiration is:

  1. Glucose + oxygen -> carbon dioxide + water + energy (ATP) Correct answer.
  2. Carbon dioxide + water -> glucose + oxygen
  3. Glucose -> lactic acid + large amount of energy
  4. Glucose + carbon dioxide -> oxygen + water

Explanation

Aerobic respiration oxidises glucose using oxygen, releasing carbon dioxide and water and transferring energy to ATP. It is essentially the reverse of the overall photosynthesis equation.

Question 31Cell structure, membranes and division

Glycolysis, the first stage of cellular respiration, occurs in the:

  1. Mitochondrial matrix
  2. Cytoplasm Correct answer.
  3. Inner mitochondrial membrane
  4. Nucleus

Explanation

Glycolysis takes place in the cytoplasm, where glucose is broken down to pyruvate with a small net gain of ATP. It does not require oxygen, which is why it is common to both aerobic and anaerobic respiration.

Question 32Cell structure, membranes and division

During vigorous exercise, human muscle cells may respire anaerobically. The product that accumulates and contributes to muscle fatigue is:

  1. Ethanol
  2. Carbon dioxide only
  3. Lactic acid Correct answer.
  4. Oxygen

Explanation

When oxygen supply cannot meet demand, muscle cells convert pyruvate to lactic acid to regenerate NAD+ so glycolysis can continue. Lactic acid accumulation is associated with fatigue, and it is later oxidised in the liver during recovery (the oxygen debt).

Question 33Cell structure, membranes and division

A respirometer containing germinating seeds and soda lime (which absorbs CO2) showed the liquid droplet moving towards the seeds over time. The best explanation is that:

  1. The seeds released oxygen, increasing gas volume
  2. The seeds absorbed oxygen for respiration while the CO2 produced was absorbed by the soda lime, reducing gas volume Correct answer.
  3. The soda lime released carbon dioxide
  4. Water evaporated from the seeds, increasing pressure

Explanation

Germinating seeds respire aerobically, taking in oxygen. The CO2 they release is absorbed by the soda lime, so total gas volume falls and atmospheric pressure pushes the droplet towards the seeds. The rate of movement estimates the respiration rate.

Question 34Cell structure, membranes and division

During which stage of mitosis do the chromosomes line up along the equator of the cell?

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

Explanation

At metaphase the chromosomes, each made of two sister chromatids, attach to spindle fibres and align at the cell's equatorial plate. This arrangement ensures that when the chromatids separate at anaphase, each daughter cell receives an identical set.

Question 35Cell structure, membranes and division

A student counted cells in an onion root tip squash: 180 cells in interphase, 25 in prophase, 10 in metaphase, 8 in anaphase, 17 in telophase (240 cells total). If one full cell cycle takes 24 hours, the best estimate of the duration of metaphase is:

  1. About 24 hours
  2. About 1 hour Correct answer.
  3. About 18 hours
  4. About 10 minutes

Explanation

The proportion of cells in a stage estimates the proportion of the cycle spent in that stage. Metaphase cells are 10/240 of the total, so 10/240 x 24 hours = 1 hour. Interphase dominates (180/240 x 24 = 18 hours), matching its known long duration.

Question 36Genetics, inheritance and molecular information

In a DNA molecule, adenine always pairs with:

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

Explanation

In DNA, complementary base pairing links adenine with thymine (two hydrogen bonds) and guanine with cytosine (three hydrogen bonds). This specific pairing allows accurate copying of the genetic code during replication. Uracil replaces thymine in RNA.

Question 37Genetics, inheritance and molecular information

A gene is best defined as:

  1. A whole chromosome
  2. A section of DNA that codes for a particular protein (polypeptide) Correct answer.
  3. Any sequence of RNA in the cytoplasm
  4. A protein found in the nucleus

Explanation

A gene is a specific sequence of DNA bases on a chromosome that carries the instructions for making one polypeptide. The sequence of bases determines the sequence of amino acids, and hence the protein's structure and function.

Question 38Genetics, inheritance and molecular information

DNA replication is described as semi-conservative because:

  1. Only half of the DNA molecule is copied each time
  2. Each new DNA molecule consists of one original (parent) strand and one newly synthesised strand Correct answer.
  3. Half of the daughter cells receive no DNA
  4. The two strands of the new molecule are both newly made

Explanation

In semi-conservative replication the double helix unwinds and each parent strand acts as a template for a new complementary strand. Each daughter molecule therefore conserves one original strand paired with one new strand, as confirmed by the Meselson-Stahl experiment.

Question 39Genetics, inheritance and molecular information

In a eukaryotic cell, transcription and translation occur, respectively, in the:

  1. Cytoplasm and nucleus
  2. Nucleus and cytoplasm (at ribosomes) Correct answer.
  3. Ribosomes and nucleus
  4. Mitochondria and chloroplasts only

Explanation

Transcription, the synthesis of messenger RNA from a DNA template, occurs in the nucleus where the chromosomes are. The mRNA then travels to the cytoplasm, where ribosomes carry out translation, assembling amino acids into a polypeptide.

Question 40Genetics, inheritance and molecular information

The genetic code is read in triplets. An mRNA codon is a sequence of:

  1. Three amino acids
  2. Three bases that codes for one amino acid Correct answer.
  3. Three genes
  4. Three nucleotides of tRNA only

Explanation

A codon is a group of three consecutive mRNA bases that specifies one amino acid (or a stop signal) during translation. With four bases there are 64 possible codons, more than enough to code for the 20 amino acids, so the code is degenerate.

Question 41Genetics, inheritance and molecular information

A point mutation changes one DNA triplet from GAA to GAG. Both triplets code for the same amino acid (glutamic acid). This type of mutation is called:

  1. A frameshift mutation
  2. A silent (same-sense) mutation Correct answer.
  3. A nonsense mutation
  4. A chromosomal deletion

Explanation

Because the genetic code is degenerate, some base substitutions leave the amino acid unchanged. Such silent mutations do not alter the protein's primary structure and usually have no effect on the phenotype.

Question 42Genetics, inheritance and molecular information

Mendel crossed pure-breeding tall pea plants with pure-breeding dwarf plants. The F1 were all tall. When the F1 were self-pollinated, the F2 phenotypic ratio was approximately:

  1. 1 tall : 1 dwarf
  2. 3 tall : 1 dwarf Correct answer.
  3. 1 tall : 3 dwarf
  4. All tall

Explanation

The F1 plants are all heterozygous (Tt). Self-pollinating Tt x Tt gives offspring genotypes 1 TT : 2 Tt : 1 tt. Because tall is dominant, TT and Tt are tall, giving the classic 3:1 phenotypic ratio in the F2.

Question 43Genetics, inheritance and molecular information

Two heterozygous parents (Aa x Aa) are crossed. The expected genotypic ratio among the offspring is:

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

Explanation

A Punnett square for Aa x Aa gives AA, Aa, Aa and aa - a genotypic ratio of 1 AA : 2 Aa : 1 aa. The familiar 3:1 figure is the phenotypic ratio when A is completely dominant.

Question 44Genetics, inheritance and molecular information

A test cross is used to determine whether an organism showing the dominant phenotype is homozygous or heterozygous. It involves crossing the organism with:

  1. Another organism showing the dominant phenotype
  2. A homozygous recessive individual Correct answer.
  3. A heterozygous individual
  4. Itself

Explanation

Crossing with a homozygous recessive (aa) reveals the unknown genotype: if the tested parent is heterozygous (Aa), half the offspring show the recessive trait; if it is homozygous dominant (AA), all offspring show the dominant trait.

Question 45Genetics, inheritance and molecular information

In a dihybrid cross between two double heterozygotes (AaBb x AaBb) with independent assortment and complete dominance, what fraction of offspring are expected to show both recessive phenotypes?

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

Explanation

For each gene, Aa x Aa gives 1/4 recessive phenotype (aa). With independent assortment the probabilities multiply: 1/4 x 1/4 = 1/16 for aabb, which shows both recessive traits. This matches the 9:3:3:1 ratio.

Question 46Genetics, inheritance and molecular information

In snapdragons, crossing red-flowered with white-flowered plants produces all pink offspring. This is an example of:

  1. Complete dominance
  2. Incomplete (partial) dominance Correct answer.
  3. Codominance
  4. Sex linkage

Explanation

In incomplete dominance the heterozygote shows an intermediate phenotype - here pink, between red and white. Neither allele is fully dominant, so the F1 blend, and the F2 give a 1 red : 2 pink : 1 white ratio.

Question 47Genetics, inheritance and molecular information

Human ABO blood groups are controlled by three alleles: IA, IB and i. A person with genotype IAIB has blood group AB because IA and IB are:

  1. Both recessive to i
  2. Codominant - both are expressed equally Correct answer.
  3. Incompletely dominant
  4. Linked on the same chromosome

Explanation

IA and IB are codominant: in the heterozygote IAIB both A and B antigens are produced on the red blood cells, giving group AB. Both IA and IB are dominant over the recessive allele i.

Question 48Genetics, inheritance and molecular information

A mother with blood group A (genotype IAi) and a father with blood group B (genotype IBi) have a child. What is the probability that the child has blood group O?

  1. 0 (impossible)
  2. 1/4 Correct answer.
  3. 1/2
  4. 3/4

Explanation

The cross IAi x IBi can produce IAIB (AB), IAi (A), IBi (B) and ii (O), each with probability 1/4. Group O requires genotype ii, receiving the recessive i allele from both parents, so the chance is 1/4.

Question 49Genetics, inheritance and molecular information

Red-green colour blindness is caused by a recessive allele on the X chromosome. A carrier mother (XBXb) and a father with normal vision (XBY) have children. Which outcome is expected?

  1. All sons will be colour blind
  2. Half the sons are expected to be colour blind; no daughters will be colour blind Correct answer.
  3. All daughters will be colour blind
  4. All children will have normal vision

Explanation

Sons inherit the Y from their father and one X from their mother, so half the sons receive Xb and are colour blind. Daughters receive the normal XB from their father, so all have normal vision, though half are carriers.

Question 50Genetics, inheritance and molecular information

In a pedigree, two unaffected parents have an affected daughter. The allele responsible is most likely:

  1. Dominant, because it appeared suddenly
  2. Recessive, because unaffected parents can both be carriers Correct answer.
  3. Carried on the Y chromosome
  4. A new chromosomal abnormality in every case

Explanation

Unaffected parents producing an affected child is the classic signature of recessive inheritance: both parents are heterozygous carriers and the child inherited two recessive alleles. A daughter being affected also rules out Y-linkage.