Grade 13 — Term 1
20 study notes · 200 practice questions · Aligned with NIE syllabus
Counted in the Idasara Academy app, which you open with a free account. The free notes, revision, practice and library pages for each lesson are linked below.
This term in the Idasara Academy app has 20 lessons (NIE Units 5, 6). For each lesson, this page gives you the points you must know and one exam-style question with its answer. None of it needs an account.
Lessons in This Term
Nervous coordination overview
What you must know
- Nervous vs Endocrine signals: Nervous communication uses electrochemical action potentials along axons and neurotransmitters across synapses (milliseconds, localized, transient); endocrine uses hormones via bloodstream (seconds to days, widespread, prolonged).
- Myelination importance: Myelin sheath formed by Schwann cells or oligodendrocytes acts as an electrical insulator, drastically speeding transmission up to 120 m/s via saltatory conduction.
- Reflex classifications: Monosynaptic reflex (knee jerk: sensory directly to motor, no interneuron) vs Polysynaptic reflex (withdrawal reflex: contains one or more interneurons).
Try one question
How does hormonal coordination differ fundamentally from nervous coordination in the human body?
- A. Hormonal signals travel much faster than saltatory nerve impulses
- B. Nervous responses have wide systemic dissemination through the lymphatic system
- C. Hormonal responses are generally slower to initiate and longer-lasting, transported via blood
- D. Hormonal responses are strictly electrical and restricted to localized target cells
Show the answer
Answer: C. Hormonal responses are generally slower to initiate and longer-lasting, transported via blood. Nervous coordination operates via rapid electrochemical action potentials targeted directly along axons, producing brief, localized effects. Hormonal coordination involves chemical messengers secreted into the bloodstream, producing slower, widespread, and prolonged physiological responses.
A model question written by Idasara on the exam pattern. It is not from a past paper.
Human nervous system structure
What you must know
- Protective coverings of CNS: Three meninges (Dura mater, Arachnoid mater, Pia mater) and Cerebrospinal Fluid (CSF) in subarachnoid space and ventricles act as shock absorber and metabolic exchange medium.
- Spinal cord cross-section anatomy: Butterfly-shaped inner Grey Matter (unmyelinated cell bodies, dorsal/ventral horns) surrounded by outer White Matter (myelinated ascending and descending nerve tracts).
- Hypothalamus homeostatic hub: Regulates body temperature, hunger, thirst, circadian rhythms, and forms the direct neuroendocrine link to the pituitary gland.
Try one question
Which part of the human brain contains the vital reflex centers that regulate heart rate, blood pressure, and breathing rhythm?
- A. Cerebellum
- B. Medulla oblongata
- C. Hypothalamus
- D. Cerebrum
Show the answer
Answer: B. Medulla oblongata. The medulla oblongata (part of the brainstem) houses autonomic reflex centers including the cardiovascular center (cardiac and vasomotor control) and respiratory rhythmicity center, essential for vegetative homeostasis.
A model question written by Idasara on the exam pattern. It is not from a past paper.
Nerve impulse generation and transmission
What you must know
- All-or-None Law: If the depolarizing stimulus does not reach threshold (-55 mV), no action potential fires; once reached, an action potential of maximal, constant amplitude is generated.
- Refractory Periods: Absolute refractory period (voltage-gated Na+ channels inactivated; impossible to fire another action potential) ensures unidirectional impulse propagation; Relative refractory period requires a stronger-than-normal stimulus.
- Excitatory vs Inhibitory Synapses: EPSPs (e.g., Acetylcholine at neuromuscular junction) depolarize postsynaptic membrane towards threshold; IPSPs (e.g., GABA) open Cl- or K+ channels, causing hyperpolarization away from threshold.
Try one question
During the depolarization phase of an action potential in a human neuron, what molecular ion movement occurs across the axolemma?
- A. Rapid efflux of K⁺ ions through voltage-gated potassium channels
- B. Passive diffusion of Cl⁻ ions into the axon
- C. Rapid influx of Na⁺ ions through voltage-gated sodium channels
- D. Active pumping of 3 Na⁺ out and 2 K⁺ in via Na⁺/K⁺ ATPase
Show the answer
Answer: C. Rapid influx of Na⁺ ions through voltage-gated sodium channels. Depolarization is caused by the rapid opening of voltage-gated sodium channels once threshold potential is reached, driving an overwhelming influx of Na⁺ down its electrochemical gradient into the intracellular fluid.
A model question written by Idasara on the exam pattern. It is not from a past paper.
Nervous system disorders
What you must know
- Stroke warning signs (FAST protocol): Facial drooping, Arm weakness, Speech difficulty, Time to call emergency services immediately; thrombolytic window is critical within 3-4.5 hours.
- Neurotransmitter deficits: Alzheimer's is linked with Acetylcholine deficiency in hippocampus; Parkinson's is linked with Dopamine deficiency in striatum.
- Blood-Brain Barrier (BBB) vulnerability: Astrocytic foot processes normally seal brain capillaries; inflammation during bacterial meningitis disrupts BBB, permitting toxic extravasation.
Try one question
Parkinson's disease is neurobiologically characterized by the progressive degeneration of dopamine-producing neurons primarily in which brain region?
- A. Vermis of the cerebellum
- B. Prefrontal cerebral cortex
- C. Substantia nigra of the midbrain (basal nuclei)
- D. Hippocampus of the limbic system
Show the answer
Answer: C. Substantia nigra of the midbrain (basal nuclei). Parkinson's disease results from the death of dopaminergic neurons in the substantia nigra, leading to dopamine deficiency in the basal nuclei and symptoms like resting tremors, rigidity, and bradykinesia.
A model question written by Idasara on the exam pattern. It is not from a past paper.
Sensory structures
What you must know
- Receptor adaptation: Phasic receptors (e.g., Pacinian corpuscles) adapt rapidly, ceasing firing during sustained stimuli; Tonic receptors (e.g., pain receptors, Merkel discs) adapt slowly or not at all, signaling continuous threat.
- Two-point discrimination threshold: Distance required to perceive two distinct tactile points is smallest on fingertips (high receptor density, small receptive fields) and largest on back/thigh (low receptor density).
- Sensory cortex somatotopic map (Sensory Homunculus): Body areas with highest tactile acuity (hands, lips, tongue) occupy disproportionately large areas of the primary somatosensory cortex.
Try one question
Which sensory receptors in human skin are encapsulated mechanoreceptors specialized for detecting deep pressure and high-frequency vibrations?
- A. Meissner's corpuscles (tactile corpuscles)
- B. Pacinian corpuscles (lamellar corpuscles)
- C. Free nerve endings
- D. Merkel discs
Show the answer
Answer: B. Pacinian corpuscles (lamellar corpuscles). Pacinian corpuscles consist of concentric layers of connective tissue surrounding a central dendrite, located deep in the dermis and hypodermis, sensitive to deep pressure and rapid vibration.
A model question written by Idasara on the exam pattern. It is not from a past paper.
Eye and ear structure and function
What you must know
- Visual defects & corrections: Myopia (nearsightedness, eyeball too long; corrected with concave diverging lens); Hyperopia (farsightedness, eyeball too short; corrected with convex converging lens); Presbyopia (aging lens loses elasticity).
- Middle ear impedance matching: The area ratio between large tympanic membrane and small oval window (~17:1), combined with ossicular lever action, magnifies sound pressure ~20-fold to move inner ear perilymph fluid.
- Fovea centralis vs Blind spot: Fovea centralis has only cones, zero rods, 1:1 ganglion ratio yielding maximum visual acuity; Optic disc (blind spot) lacks photoreceptors because optic nerve axons exit eye.
Try one question
In the human eye, what structural changes occur in the ciliary muscle and suspensory ligaments during accommodation for viewing nearby objects?
- A. Ciliary muscles contract, suspensory ligaments tighten, lens becomes flatter
- B. Ciliary muscles contract, suspensory ligaments relax, lens becomes more convex
- C. Ciliary muscles relax, suspensory ligaments relax, lens becomes more convex
- D. Ciliary muscles relax, suspensory ligaments tighten, lens becomes flatter
Show the answer
Answer: B. Ciliary muscles contract, suspensory ligaments relax, lens becomes more convex. For near vision, the ciliary muscle contracts, reducing tension on the suspensory ligaments (zonules). This allows the elastic crystalline lens to round up and become more convex, increasing its refractive power.
A model question written by Idasara on the exam pattern. It is not from a past paper.
Endocrine system
What you must know
- Negative feedback loops: Elevated levels of target hormones (e.g., T3/T4 or Cortisol) inhibit the release of their corresponding trophic hormones from both hypothalamus (TRH, CRH) and anterior pituitary (TSH, ACTH).
- Calcium homeostasis antagonism: Calcitonin (from thyroid C cells) deposits Ca2+ in bone; Parathyroid Hormone (PTH) stimulates osteoclasts to dissolve bone matrix and activates vitamin D to calcitriol in kidneys, elevating blood Ca2+.
- Islets of Langerhans dual control: Beta cells secrete Insulin (hypoglycemic: stimulates glycogenesis, GLUT4 translocation, inhibits gluconeogenesis); Alpha cells secrete Glucagon (hyperglycemic: promotes glycogenolysis and gluconeogenesis).
Try one question
Which hormone is secreted by the adrenal cortex to stimulate sodium reabsorption and potassium excretion in the distal convoluted tubules of the kidney?
- A. Cortisol
- B. Aldosterone
- C. Atrial natriuretic peptide (ANP)
- D. Antidiuretic hormone (ADH)
Show the answer
Answer: B. Aldosterone. Aldosterone is a mineralocorticoid secreted by the adrenal cortex (zona glomerulosa) that acts on the distal tubules and collecting ducts of the nephron to stimulate Na⁺ retention and K⁺ excretion, regulating blood volume and pressure.
A model question written by Idasara on the exam pattern. It is not from a past paper.
Homeostasis
What you must know
- Negative vs Positive Feedback: Negative feedback counteracts disturbances to restore equilibrium; Positive feedback amplifies deviations until a climactic event occurs (e.g., oxytocin during labor contractions, LH surge in ovulation, platelet plug formation).
- Countercurrent multiplier in kidney: Loop of Henle establishes hyperosmotic medullary gradient (up to 1200 mOsm/L), creating the osmotic driving force required for ADH-mediated water reabsorption in collecting ducts.
- Ectothermy vs Endothermy: Endotherms (mammals, birds) generate internal metabolic heat to maintain constant core body temperature; ectotherms rely on behavioral adaptations to absorb environmental heat.
Try one question
When human core body temperature rises above 37 °C, which physiological negative feedback responses are triggered by the thermoregulatory center in the anterior hypothalamus?
- A. Decreased respiration rate and lipolysis of brown adipose tissue
- B. Piloerection (goosebumps) and release of thyroxine
- C. Cutaneous vasoconstriction and shivering thermogenesis
- D. Cutaneous vasodilation and increased sweat gland secretion
Show the answer
Answer: D. Cutaneous vasodilation and increased sweat gland secretion. The heat-loss center in the anterior hypothalamus initiates cutaneous vasodilation (increasing blood flow to skin for radiative/conductive heat dissipation) and stimulates eccrine sweat glands to promote evaporative cooling.
A model question written by Idasara on the exam pattern. It is not from a past paper.
Types of reproduction in animals
What you must know
- Developmental patterns after fertilization: Oviparity (eggs laid outside, embryonic development fueled by yolk, e.g., birds, most reptiles); Viviparity (embryo develops inside maternal uterus with placental nutrition, giving live birth, e.g., eutherian mammals); Ovoviviparity (eggs retained in mother's body until hatching, nourished by yolk, e.g., certain sharks, vipers).
- Hermaphroditism (Monoecy): Organisms possessing both male and female gonads (e.g., earthworms, tapeworms); allows self-fertilization in isolated conditions or reciprocal cross-fertilization doubling reproductive output.
- Evolutionary trade-offs: Asexual reproduction saves energy and time (no mate seeking, 100% maternal gene transmission); sexual reproduction incurs 'two-fold cost of sex' but purges deleterious mutations and creates environmental adaptation plasticity.
Try one question
Which form of asexual reproduction in animals involves the development of an unfertilized egg into a viable adult individual, as observed in honeybee drones?
- A. Budding
- B. Parthenogenesis
- C. Fragmentation
- D. Multiple fission
Show the answer
Answer: B. Parthenogenesis. Parthenogenesis is a form of asexual reproduction wherein an embryo develops from an unfertilized ovum without participation of a male gamete. In honeybees (haplodiploidy), unfertilized haploid eggs develop into fertile males (drones).
A model question written by Idasara on the exam pattern. It is not from a past paper.
Male reproductive system
What you must know
- Hormonal axis in males: GnRH from hypothalamus stimulates anterior pituitary to secrete FSH (stimulates Sertoli cells for spermatogenesis) and LH (stimulates Leydig cells to produce Testosterone); Testosterone and Inhibin exert negative feedback on hypothalamus and pituitary.
- Sperm ultrastructure: Head contains haploid nucleus and Acrosome (hydrolytic enzymes like hyaluronidase for egg penetration); Midpiece packed with mitochondria for ATP generation; Tail (flagellum with 9+2 axoneme) for motility.
- Spermatogenesis vs Spermiogenesis: Spermatogenesis is the complete developmental sequence from spermatogonium to mature sperm; Spermiogenesis is the specific maturation phase converting non-motile spermatids into flagellated spermatozoa.
Try one question
Which cells located in the interstitial tissue between the seminiferous tubules of the human testes are responsible for synthesizing and secreting testosterone?
- A. Primary spermatocytes
- B. Leydig cells (interstitial cells)
- C. Spermatogonia
- D. Sertoli cells (sustentacular cells)
Show the answer
Answer: B. Leydig cells (interstitial cells). Leydig (interstitial) cells reside in the connective tissue between seminiferous tubules and produce testosterone in response to Luteinizing Hormone (LH) from the anterior pituitary. Sertoli cells nourish developing spermatocytes.
A model question written by Idasara on the exam pattern. It is not from a past paper.
Female reproductive system
What you must know
- LH Surge triggers Ovulation: High sustained levels of estrogen at end of follicular phase switch from negative to positive feedback, triggering a massive spike in LH (and FSH) around day 14, rupturing the mature Graafian follicle.
- Fate of Corpus Luteum: If fertilization does not occur, LH drops, corpus luteum degenerates into Corpus Albicans, progesterone and estrogen crash, triggering endometrial breakdown (menstruation); if fertilization occurs, hCG from trophoblast rescues corpus luteum.
- Fertilization site: Occurs precisely in the Ampulla of the Fallopian tube; secondary oocyte completes meiosis II only upon sperm entry.
Try one question
Which endocrine event directly triggers ovulation (release of the secondary oocyte from the Graafian follicle) during the human ovarian cycle?
- A. Peak secretion of human chorionic gonadotropin (hCG)
- B. Luteinizing hormone (LH) surge
- C. Sudden drop in progesterone concentration
- D. Inhibition of follicle-stimulating hormone (FSH) by inhibin
Show the answer
Answer: B. Luteinizing hormone (LH) surge. High concentrations of estrogen secreted by the mature Graafian follicle exert positive feedback on the anterior pituitary and hypothalamus, causing a dramatic surge in Luteinizing Hormone (LH) around day 14 of a typical 28-day cycle, which triggers rupture of the follicle and ovulation.
A model question written by Idasara on the exam pattern. It is not from a past paper.
Fertilization to birth
What you must know
- Three germ layers formed during Gastrulation: Ectoderm (nervous system, epidermis, sensory organs), Mesoderm (skeletal system, muscles, circulatory/lymphatic systems, kidneys), and Endoderm (epithelial lining of digestive, respiratory tracts, liver, pancreas).
- hCG diagnostic indicator: Presence of hCG in maternal urine/blood within 10-14 days forms the biochemical basis for standard home pregnancy tests.
- Three stages of Labor: 1) Dilation stage (cervix dilates to 10 cm, amnion ruptures), 2) Expulsion stage (strong uterine and abdominal contractions deliver baby), 3) Placental stage (delivery of placenta / afterbirth within 15-30 min).
Try one question
What is the primary cellular mechanism that establishes the slow block to polyspermy immediately following the fusion of a sperm with the human egg membrane?
- A. Rapid depolarization of the ovum plasma membrane by sodium influx
- B. Secretion of human placental lactogen by trophoblast cells
- C. Immediate breakdown of the acrosomal vesicle by hyaluronidase
- D. Cortical reaction resulting in the hardening of the zona pellucida
Show the answer
Answer: D. Cortical reaction resulting in the hardening of the zona pellucida. Upon sperm-egg membrane fusion, an intracellular calcium wave triggers exocytosis of cortical granules (cortical reaction). The released enzymes modify sperm receptors and harden the zona pellucida into a fertilization envelope, establishing the permanent slow block to polyspermy.
A model question written by Idasara on the exam pattern. It is not from a past paper.
Reproductive health
What you must know
- Barrier dual protection: Male and female condoms are the ONLY contraceptive methods that provide significant dual protection against both unintended pregnancy and sexually transmitted infections (STIs/HIV).
- Hormonal pill mechanism: Combination pills (synthetic estrogen + progestin) inhibit pituitary secretion of FSH and LH, preventing follicular maturation and ovulation, while thickening cervical mucus to block sperm motility.
- Vasectomy vs Tubal ligation: Vasectomy severs/ties the vas deferens (ejaculation still occurs with seminal fluid but zero sperm); Tubal ligation cuts/occludes the Fallopian tubes, preventing sperm from meeting ovum.
Try one question
Which sexually transmitted infection (STI) is caused by the spirochete bacterium Treponema pallidum and typically manifests in its primary stage as a painless ulcerated chancre?
- A. Syphilis
- B. Trichomoniasis
- C. Gonorrhoea
- D. Genital herpes
Show the answer
Answer: A. Syphilis. Syphilis is caused by the helical bacterium Treponema pallidum. Primary syphilis presents with a solitary, painless genital ulcer (chancre); secondary syphilis involves skin rashes; tertiary syphilis causes systemic cardiovascular and neurological damage (gummas, neurosyphilis).
A model question written by Idasara on the exam pattern. It is not from a past paper.
Skeletal systems and movement
What you must know
- Cartilage vs Bone: Cartilage is non-vascularized, flexible connective tissue composed of chondrocytes in chondroitin sulfate matrix; Bone is highly vascularized, rigid tissue with osteocytes in mineralized hydroxyapatite (calcium phosphate) and collagen matrix arranged in osteons (Haversian systems).
- Ecdysis vulnerability: Immediately after molting, arthropods have soft, unsclerotized cuticles, rendering them highly vulnerable to predators and mechanical damage until tanning hardens the new exoskeleton.
- Bone remodeling cellular triad: Osteoblasts synthesize and mineralize new bone matrix; Osteocytes maintain mature bone tissue; Osteoclasts (multinucleated macrophages) resorb/dissolve bone during remodeling and calcium regulation.
Try one question
Which skeletal support system relies on an incompressible fluid enclosed in a closed body compartment against which antagonistic muscle layers exert pressure to effect locomotion?
- A. Hydrostatic skeleton
- B. Chitinous exoskeleton
- C. Endochondral endoskeleton
- D. Calcareous shell
Show the answer
Answer: A. Hydrostatic skeleton. A hydrostatic skeleton consists of fluid under pressure in a closed body cavity (e.g., coelom in annelids like the earthworm). Alternating contractions of circular and longitudinal muscles against the incompressible hydrostatic fluid generate peristaltic waves for movement.
A model question written by Idasara on the exam pattern. It is not from a past paper.
Axial skeleton
What you must know
- Intervertebral discs structure: Outer fibrous annulus fibrosus surrounding inner gel-like nucleus pulposus; act as shock absorbers; herniation ('slipped disc') compresses adjacent spinal nerves causing sciatica.
- Atlas (C1) and Axis (C2) functional anatomy: Atlanto-occipital joint allows sagittal nodding ('Yes' motion); Atlanto-axial joint (dens/odontoid process pivoting in atlas ring) allows rotational head movement ('No' motion).
- Primary vs Secondary spinal curvatures: Primary kyphotic curves (thoracic, sacral) retain fetal anterior concavity; secondary lordotic curves (cervical, lumbar) develop anterior convexity postnatally during motor milestones.
Try one question
Which structural feature is unique to human cervical vertebrae (C3–C6) and distinguishes them from all thoracic and lumbar vertebrae?
- A. Fused vertebrae forming a triangular dorsal wedge
- B. Presence of articular costal facets on the centrum and transverse processes
- C. Large kidney-shaped vertebral body without any foramina
- D. Presence of transverse foramina (foramina transversaria) and bifid spinous processes
Show the answer
Answer: D. Presence of transverse foramina (foramina transversaria) and bifid spinous processes. Cervical vertebrae (C1–C7) uniquely possess transverse foramina through which the vertebral arteries ascend to the brain. In addition, vertebrae C2 to C6 typically feature bifid (split) spinous processes and small, oval centra.
A model question written by Idasara on the exam pattern. It is not from a past paper.
Appendicular skeleton
What you must know
- Shoulder vs Hip joint mobility/stability tradeoff: Shoulder joint (shallow glenoid fossa) provides extreme range of multiaxial motion at the expense of dislocation vulnerability; Hip joint (deep acetabulum cup + powerful iliofemoral ligaments) maximizes stability and weight-bearing at the expense of mobility.
- Male vs Female pelvis distinctions: Female pelvis is broader, lighter, and shallower, with an oval/round pelvic inlet, wider pelvic outlet, greater sciatic notch >90°, and pubic arch angle >90° (vs <90° in males) adapted for childbearing.
- Foot arch functional biomechanics: Three arches (medial longitudinal, lateral longitudinal, transverse) maintained by bones, plantar ligaments, and tendons distribute body weight and act as dynamic springs during walking and running.
Try one question
In the human appendicular skeleton, which cup-shaped socket articulates with the head of the femur to form the hip joint, and what bones fuse to form it?
- A. Acetabulum formed by the fusion of the ilium, ischium, and pubis
- B. Obturator foramen formed by the ischium and pubis
- C. Olecranon fossa formed by the radius and ulna
- D. Glenoid cavity formed by the fusion of the clavicle and scapula
Show the answer
Answer: A. Acetabulum formed by the fusion of the ilium, ischium, and pubis. The acetabulum is a deep hemispherical cup on the lateral surface of the coxal (hip) bone formed by the confluence of the ilium, ischium, and pubis. It receives the spherical head of the femur to form the multiaxial ball-and-socket hip joint.
A model question written by Idasara on the exam pattern. It is not from a past paper.
Joints and muscle movement
What you must know
- Rigor Mortis mechanism: Following death, ATP synthesis ceases completely; without fresh ATP to bind myosin heads, cross-bridges remain locked to actin filaments, producing muscular stiffness until proteolytic decomposition sets in ~12-24 hours later.
- Antagonistic muscle pairs: Skeletal muscles can only pull (contract actively), not push; locomotion requires paired antagonistic muscles acting around joints (e.g., Biceps brachii flexes elbow while Triceps brachii extends elbow).
- Motor Unit recruitment: A motor unit consists of a single somatic motor neuron and all muscle fibers it innervates; fine motor control uses small motor units (e.g., 2-5 fibers in eye muscles), while gross power uses large units (e.g., 1000+ fibers in gastrocnemius).
Try one question
According to the sliding filament model of skeletal muscle contraction, what direct event causes the myosin head to detach from the active binding site on actin?
- A. Binding of a new ATP molecule to the myosin head
- B. Hydrolysis of bound ATP into ADP and inorganic phosphate
- C. Release of calcium ions from the sarcoplasmic reticulum
- D. Phosphorylation of troponin by creatine kinase
Show the answer
Answer: A. Binding of a new ATP molecule to the myosin head. Following the power stroke, a new molecule of ATP binds to the nucleotide-binding site on the myosin head. This causes an allosteric conformational change that drastically reduces myosin's affinity for actin, causing the cross-bridge to detach. Without ATP, detachment cannot occur (rigor mortis).
A model question written by Idasara on the exam pattern. It is not from a past paper.
Mendel's experiments
What you must know
- Test cross principle: Crossing an individual showing a dominant phenotype with a homozygous recessive individual (e.g., T_ × tt) to determine whether the dominant genotype is homozygous (TT) or heterozygous (Tt).
- Punnett square construction: Always show parental genotypes, gamete types in circles, and clear offspring genotype/phenotype distinctions to earn full structured essay marks.
- Reasons for Mendel's success: Pisum sativum was self-pollinating, easy to cultivate, had short generation times, and exhibited clear, non-overlapping contrasting traits.
Try one question
In a dihybrid cross between two heterozygous garden pea plants (RrYy × RrYy), what proportion of the F₂ offspring is expected to exhibit the recombinant phenotypes?
- A. 1/16
- B. 6/16
- C. 9/16
- D. 10/16
Show the answer
Answer: B. 6/16. In Mendel's dihybrid cross, parental phenotypes are round-yellow (9/16) and wrinkled-green (1/16). Recombinant (non-parental) phenotypes are round-green (3/16) and wrinkled-yellow (3/16). Total recombinants = 3/16 + 3/16 = 6/16 (3/8).
A model question written by Idasara on the exam pattern. It is not from a past paper.
Non-Mendelian genetics
What you must know
- ABO blood group genetics table: Blood group A = IAIA or IAi; Blood group B = IBIB or IBi; Blood group AB = IAIB (codominant); Blood group O = ii (universal donor).
- Criss-cross inheritance of X-linked traits: Carrier mothers pass the recessive trait to 50% of their sons; affected fathers cannot pass X-linked traits to sons (only to daughters as carriers).
- Epistasis and gene interaction: One gene masks or modifies the phenotypic expression of a second independent gene (deviating from 9:3:3:1 dihybrid ratio to 9:7, 12:3:1, or 9:3:4).
Try one question
A woman with blood group A whose father had blood group O marries a man with blood group B whose mother had blood group O. What is the probability that their first child will have blood group O?
- A. 1/8 (12.5%)
- B. 1/2 (50%)
- C. 0 (0%)
- D. 1/4 (25%)
Show the answer
Answer: D. 1/4 (25%). The woman has genotype I^A i (inherited allele i from her O father). The man has genotype I^B i (inherited allele i from his O mother). The Punnett cross (I^A i × I^B i) produces genotypes I^A I^B (AB), I^A i (A), I^B i (B), and ii (O) in equal 1/4 proportions. Probability of group O (ii) is 1/4.
A model question written by Idasara on the exam pattern. It is not from a past paper.
Evolution and gene frequencies
What you must know
- Hardy-Weinberg problem-solving algorithm: ALWAYS calculate q² (frequency of homozygous recessives) first, take the square root to find q, calculate p = 1 - q, then determine 2pq (heterozygote frequency).
- Genetic drift vs Natural selection: Genetic drift is purely CHANCE-driven occurring prominently in SMALL populations; natural selection is adaptive and non-random.
- Speciation concepts: Allopatric speciation involves geographical isolation barriers; Sympatric speciation occurs within the same geographic area (often via polyploidy in plants).
Try one question
In a population in Hardy-Weinberg equilibrium, the frequency of individuals affected by an autosomal recessive condition is 0.04. What is the frequency of heterozygous carriers in this population?
- A. 0.08
- B. 0.64
- C. 0.32
- D. 0.16
Show the answer
Answer: C. 0.32. q² = 0.04 → q = 0.2. Since p + q = 1, p = 1 - 0.2 = 0.8. Frequency of heterozygous carriers (2pq) = 2 × 0.8 × 0.2 = 0.32 (32%).
A model question written by Idasara on the exam pattern. It is not from a past paper.
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