BIO301 — Essentials of Genetics: Midterm & Finalterm Solved MCQs and Subjective

BIO301 Essentials of Genetics covers heredity and variation, Mendel's laws, monohybrid and dihybrid crosses, incomplete dominance and co-dominance, linkage, epistasis, pleiotropy, polygenic traits, mutation and sex-linked inheritance. This solved post gives you 30 verified items for Virtual University of Pakistan: 10 Midterm MCQs from Lectures 1-22, 10 Finalterm MCQs from Lectures 23-45, and 5 Midterm plus 5 Finalterm subjective questions, each with its correct answer and handout reference. Practice every question instantly in the quiz for this course. Take the quiz: https://virtualustaad.blogspot.com/p/solvedmcqs.html?code=BIO301

1. Midterm Solved MCQs

Q1. Genetics is best defined as the branch of biology concerned with:
A) The naming and classification of organisms
B) Heredity and variation
C) The structure of cells
D) The evolution of species only.
Correct answer: B — Heredity and variation.
Reference: VU handout — Genetics: definition, types of genetics, genetics terminologies.

Q2. The genetic constitution (make-up) of an organism is called its:
A) Phenotype
B) Genotype
C) Karyotype
D) Allele.
Correct answer: B — Genotype.
Reference: VU handout — Genetics terminologies.

Q3. In a heterozygous organism, the allele that is expressed in the phenotype is the:
A) Recessive allele
B) Dominant allele
C) Mutant allele
D) Lethal allele.
Correct answer: B — Dominant allele.
Reference: VU handout — Mendel's law of dominance.

Q4. In a monohybrid cross between two heterozygous parents (Aa × Aa), the expected phenotypic ratio in the offspring is:
A) 1:1
B) 1:2:1
C) 3:1
D) 9:3:3:1.
Correct answer: C — 3:1.
Reference: VU handout — Monohybrid cross.

Q5. In a dihybrid cross between two heterozygous parents (AaBb × AaBb), the expected phenotypic ratio in the offspring is:
A) 3:1
B) 1:2:1
C) 9:3:3:1
D) 1:1:1:1.
Correct answer: C — 9:3:3:1.
Reference: VU handout — Dihybrid cross.

Q6. Mendel's law of dominance states that:
A) The two alleles of a gene separate during gamete formation
B) Alleles of different genes assort independently
C) In a heterozygote, one allele masks the expression of the other
D) Genes on the same chromosome are inherited together.
Correct answer: C — In a heterozygote, one allele masks the expression of the other.
Reference: VU handout — Mendel's law of dominance.

Q7. When homozygous red snapdragons are crossed with homozygous white snapdragons, all the offspring have pink flowers. This is an example of:
A) Complete dominance
B) Incomplete dominance
C) Co-dominance
D) Epistasis.
Correct answer: B — Incomplete dominance.
Reference: VU handout — Exceptions to Mendelian inheritance: incomplete dominance.

Q8. A person with blood group AB has both A and B antigens on their red blood cells. This is an example of:
A) Incomplete dominance
B) Co-dominance
C) Epistasis
D) Pleiotropy.
Correct answer: B — Co-dominance.
Reference: VU handout — Exceptions to Mendelian inheritance: co-dominance.

Q9. A test cross is a cross between an organism showing the dominant phenotype and:
A) A homozygous dominant organism
B) A homozygous recessive organism
C) Another heterozygous organism
D) An organism of the opposite sex only.
Correct answer: B — A homozygous recessive organism.
Reference: VU handout — Monohybrid cross; test cross.

Q10. Mendel's law of independent assortment states that:
A) The two alleles of a gene separate during gamete formation
B) Alleles of different genes (on different chromosomes) sort into gametes independently of each other
C) Dominant alleles always mask recessive alleles
D) Linked genes are inherited together.
Correct answer: B — Alleles of different genes (on different chromosomes) sort into gametes independently of each other.
Reference: VU handout — Mendel's law of independent assortment.

2. Finalterm Solved MCQs

Q1. Two genes located close together on the same chromosome are said to be linked. Compared with unlinked genes, linked genes show:
A) A recombination frequency of exactly 50%
B) A recombination frequency of less than 50%
C) A recombination frequency of more than 50%
D) No crossing over at all.
Correct answer: B — A recombination frequency of less than 50%.
Reference: VU handout — Linkage; chromosomes.

Q2. Epistasis occurs when:
A) One gene affects many traits
B) One gene masks or modifies the expression of another (non-allelic) gene
C) Two alleles of the same gene are both expressed
D) A trait is controlled by many genes.
Correct answer: B — One gene masks or modifies the expression of another (non-allelic) gene.
Reference: VU handout — Epistasis.

Q3. A single gene that affects two or more apparently unrelated traits is an example of:
A) Epistasis
B) Pleiotropy
C) Polygenic inheritance
D) Co-dominance.
Correct answer: B — Pleiotropy.
Reference: VU handout — Pleiotropy.

Q4. Human height and skin colour show continuous variation and are controlled by many genes, each with a small effect. Such traits are called:
A) Mendelian traits
B) Polygenic traits
C) Sex-linked traits
D) Epistatic traits.
Correct answer: B — Polygenic traits.
Reference: VU handout — Polygenic traits.

Q5. The haploid chromosome number in human gametes (sperm and egg) is:
A) 46
B) 44
C) 23
D) 92.
Correct answer: C — 23.
Reference: VU handout — Chromosomes; cell, nucleus.

Q6. Haemophilia is an X-linked recessive disorder. It is much more common in males than in females because:
A) Males have two X chromosomes
B) Males have only one X chromosome, so a single recessive allele on it is expressed
C) The gene is carried on the Y chromosome
D) Females cannot inherit the allele.
Correct answer: B — Males have only one X chromosome, so a single recessive allele on it is expressed.
Reference: VU handout — Sex-linked inheritance; chromosomes.

Q7. A mutation in which the insertion or deletion of one or two nucleotides shifts the reading frame of a gene is called a:
A) Silent mutation
B) Missense mutation
C) Frameshift mutation
D) Nonsense mutation.
Correct answer: C — Frameshift mutation.
Reference: VU handout — Mutation; variation.

Q8. The ABO blood group system in humans is an example of multiple alleles, because:
A) There is only one allele in the population
B) There are three alleles (IA, IB and i) at the same locus in the population
C) Blood group is controlled by the environment
D) Every person carries all three alleles.
Correct answer: B — There are three alleles (IA, IB and i) at the same locus in the population.
Reference: VU handout — Multiple alleles; co-dominance.

Q9. In a pedigree, an autosomal recessive disorder typically shows the pattern that:
A) Affected individuals always have an affected parent
B) Affected children are often born to two unaffected (carrier) parents
C) Only males are affected
D) The trait appears in every generation.
Correct answer: B — Affected children are often born to two unaffected (carrier) parents.
Reference: VU handout — Pedigree analysis; Mendelian inheritance in humans.

Q10. The coat colour of the Himalayan rabbit is white on the warm parts of the body but dark on the cooler extremities (ears, nose, feet). This shows that:
A) Genes are not involved in coat colour
B) The environment (temperature) can affect how a gene is expressed
C) The rabbit has two different genotypes
D) Coat colour is determined by the diet alone.
Correct answer: B — The environment (temperature) can affect how a gene is expressed.
Reference: VU handout — Environmental effects on gene expression.

3. Midterm Subjective

Q1. Why did Mendel choose the garden pea plant for his experiments? Describe a monohybrid cross and explain the 3:1 ratio in the F2 generation.
Answer: Mendel chose the garden pea (Pisum sativum) because it had several advantages: it is easy to grow and produces many offspring; it has distinct, contrasting traits that are easy to score (e.g. round vs wrinkled seeds, purple vs white flowers); it can self-fertilise, so true-breeding lines can be made, but it can also be cross-fertilised by hand after removing the anthers; and it has a short generation time. Mendel studied seven pairs of contrasting traits. A monohybrid cross follows one trait, e.g. seed shape. Parental cross: true-breeding round (RR) × true-breeding wrinkled (rr). All F1 offspring are Rr and have round seeds, because R is dominant over r — this is the law of dominance. When the F1 plants are self-crossed (Rr × Rr), each parent produces R and r gametes in equal numbers; the Punnett square gives RR, Rr, Rr, rr — a genotypic ratio of 1:2:1 and a phenotypic ratio of 3 round : 1 wrinkled, because both RR and Rr plants look round. This result demonstrated the law of segregation: the two alleles of a gene separate during gamete formation, so each gamete carries only one allele.
Reference: VU handout — Mendel's work; monohybrid cross; Mendel's law of segregation.

Q2. Distinguish incomplete dominance from co-dominance, giving one example of each.
Answer: Both are exceptions to simple Mendelian dominance, but they differ in what the heterozygote looks like. In incomplete dominance, neither allele is fully dominant, so the heterozygote has an intermediate phenotype between the two parents. Example: snapdragons — crossing homozygous red (RR) with homozygous white (rr) gives all pink (Rr) offspring; the red pigment is produced at half the amount, giving an intermediate colour. In co-dominance, both alleles are fully expressed in the heterozygote, so both parental traits appear side by side rather than blending. Example: ABO blood groups — a person with genotype IAIB has both A and B antigens on their red blood cells; neither antigen is masked. Another example is the roan coat of cattle (red and white hairs together). In short: incomplete dominance blends the two traits into an intermediate form, while co-dominance shows both traits fully at the same time. Both still follow Mendel's law of segregation — the alleles still separate into gametes in equal numbers — so they are not violations of Mendel's laws but extensions of them.
Reference: VU handout — Exceptions to Mendelian inheritance: incomplete dominance; co-dominance.

Q3. Explain Mendel's law of independent assortment with a dihybrid cross, and show how the 9:3:3:1 ratio arises.
Answer: The law of independent assortment states that the alleles of different genes sort into gametes independently of each other, provided the genes are on different chromosomes. Mendel showed this with a dihybrid cross in peas, following seed shape (round R dominant over wrinkled r) and seed colour (yellow Y dominant over green y). Parental cross: true-breeding round yellow (RRYY) × wrinkled green (rryy). All F1 plants are RrYy and have round yellow seeds. When the F1 plants are self-crossed (RrYy × RrYy), each parent produces four kinds of gametes — RY, Ry, rY, ry — in equal numbers, because the R/r pair and the Y/y pair assort independently. The 4 × 4 Punnett square has 16 combinations: 9 with at least one R and one Y (round yellow), 3 with R but yy (round green), 3 with rr but Y (wrinkled yellow), and 1 rryy (wrinkled green) — the classic 9:3:3:1 phenotypic ratio. This result only holds for genes on different chromosomes (or far apart on the same chromosome); genes close together on the same chromosome are linked and do not assort independently, which Mendel did not observe because the traits he chose happened to be on different chromosomes.
Reference: VU handout — Dihybrid cross; Mendel's law of independent assortment.

Q4. What is a test cross, and what is a backcross? Explain the purpose of each with an example.
Answer: A test cross is used to find out the genotype of an organism that shows the dominant phenotype: it is crossed with a homozygous recessive organism (the tester). Because the tester contributes only recessive alleles, the offspring's phenotypes directly reveal the gametes of the tested parent. Example: a tall pea plant (which could be TT or Tt) is crossed with a dwarf plant (tt). If all the offspring are tall, the parent was TT; if about half are tall and half are dwarf, the parent was Tt. A backcross is a cross between an offspring (usually an F1 hybrid) and one of its parents (or an organism with the parental genotype). Its purposes are: (1) in breeding, to transfer a desired trait (e.g. disease resistance) from a donor into an elite variety by repeatedly backcrossing to the elite parent while selecting for the trait; and (2) in genetics, to test for linkage — a test cross of a dihybrid is also a backcross, and the proportions of parental and recombinant offspring reveal whether the genes are linked. In short: a test cross answers "what is this individual's genotype?", while a backcross is a breeding tool for recovering a parental genotype with one added trait.
Reference: VU handout — Monohybrid and dihybrid crosses; test cross.

Q5. State the chromosome theory of inheritance and explain the evidence for it.
Answer: The chromosome theory of inheritance (Sutton and Boveri, 1902–1903) states that genes are located on chromosomes, and that the behaviour of chromosomes during meiosis explains Mendel's laws: chromosomes occur in homologous pairs (like Mendel's paired factors); they separate during meiosis (explaining segregation); and different chromosome pairs assort independently (explaining independent assortment). Evidence: (1) The number of linkage groups in an organism equals its haploid chromosome number — Morgan's work on Drosophila showed that genes fall into four linkage groups, matching the four pairs of chromosomes. (2) Morgan's white-eye experiments: the white-eye trait in Drosophila is inherited together with the X chromosome — a male receives his X chromosome only from his mother, and the trait followed exactly that pattern, showing that a gene is carried on a particular chromosome. (3) Cytological observations: the behaviour of chromosomes in meiosis (pairing of homologues, separation in anaphase I, independent alignment on the metaphase plate) mirrors the behaviour Mendel predicted for his factors. (4) Later, the discovery that DNA is the genetic material, and that genes are segments of DNA on chromosomes, confirmed the theory at the molecular level. The chromosome theory therefore joined Mendel's abstract factors to real, observable structures in the cell.
Reference: VU handout — What are chromosomes; cell, nucleus.

4. Finalterm Subjective

Q1. What is epistasis? Explain recessive epistasis with the example of coat colour in mice.
Answer: Epistasis is a form of gene interaction in which the allele of one gene masks or modifies the expression of another, non-allelic gene. The gene that does the masking is called epistatic, and the gene that is masked is hypostatic. It differs from dominance, which is an interaction between alleles of the same gene; epistasis is an interaction between different genes. Example — coat colour in mice (recessive epistasis): one gene (A) controls the pigment type — A gives black pigment (agouti/black) and a gives brown; a second gene (C) controls whether any pigment is made at all — C allows pigment production, while the recessive cc blocks pigment production entirely. In a dihybrid cross (AaCc × AaCc), the F2 ratio is modified from 9:3:3:1 to 9:3:4: 9 A_C_ are black, 3 aaC_ are brown, and 4 (3 A_cc + 1 aacc) are albino/white, because any mouse that is cc is white regardless of its A gene — the cc genotype is epistatic to the A gene. So the coat-colour genes are inherited in a Mendelian way, but their interaction produces a 9:3:4 ratio instead of 9:3:3:1. Epistasis is common in biochemical pathways: if an early step in a pathway is blocked, later genes in the pathway have nothing to act on, so their alleles make no difference.
Reference: VU handout — Epistasis.

Q2. Explain sex-linked inheritance using haemophilia and red–green colour blindness as examples. Why are males more often affected?
Answer: Sex-linked inheritance involves genes carried on the sex chromosomes, almost always the X chromosome (the Y chromosome carries very few genes). Haemophilia (failure of blood to clot) and red–green colour blindness are both caused by recessive alleles on the X chromosome. Because males have only one X chromosome (XY), they are hemizygous: a single recessive allele on their X chromosome is enough to cause the disorder, since there is no second X to carry a normal allele. Females (XX) need two copies of the recessive allele to be affected; with one copy they are carriers — usually unaffected themselves, but they can pass the allele to their children. A carrier mother (XHXh) has a 50% chance of passing the affected X to each son (who will be affected) and a 50% chance of passing it to each daughter (who will be a carrier). An affected father passes his X chromosome to all his daughters (who become carriers) and his Y chromosome to all his sons (who are unaffected by that gene). This is why X-linked recessive disorders are much more common in males and are typically passed from a carrier mother to her sons, often skipping a generation in the pedigree. By contrast, X-linked dominant traits and Y-linked traits (passed from father to son only) show different pedigree patterns.
Reference: VU handout — Sex-linked inheritance; chromosomes.

Q3. What is polygenic inheritance? Explain it with human skin colour as an example, and contrast it with Mendelian inheritance.
Answer: Polygenic inheritance is the control of a trait by many genes, each contributing a small, additive effect, rather than by one gene with two alleles. The result is continuous variation: instead of a few distinct classes (e.g. round vs wrinkled), the trait varies smoothly across a range, and most individuals fall in the middle, giving a bell-shaped distribution. Example — human skin colour: it is influenced by several genes controlling melanin production. If we simplify to three genes (A, B, C), each with a "dark" allele adding one unit of melanin and a "light" allele adding none, the number of dark alleles (0 to 6) determines the shade; the darkest and lightest extremes are rare (only one genotype each) while intermediate shades are common, because many genotypes give intermediate numbers of dark alleles. The same pattern is seen in human height, and in crop traits such as grain yield. Contrast with Mendelian inheritance: a Mendelian trait is controlled by one gene, shows discontinuous variation (a few clear classes), and gives predictable ratios such as 3:1 or 9:3:3:1; a polygenic trait is controlled by many genes, shows continuous variation, is strongly influenced by the environment (e.g. nutrition affects height), and is studied with statistics (means, variances) rather than simple ratios. Polygenic traits are therefore the bridge between Mendelian genetics and the quantitative genetics used in plant and animal breeding.
Reference: VU handout — Polygenic traits; types of variation.

Q4. Describe the main types of gene mutation and their consequences: point mutations (silent, missense, nonsense), frameshift mutations and chromosomal mutations. Illustrate with sickle-cell anaemia.
Answer: A mutation is a heritable change in the DNA sequence. (1) Point mutations change a single base. A silent mutation changes a codon to one that codes for the same amino acid (because the genetic code is degenerate), so the protein is unchanged. A missense mutation changes a codon to one for a different amino acid, which may alter the protein's function. A nonsense mutation changes a codon into a stop codon, producing a shortened, usually non-functional protein. (2) Frameshift mutations are insertions or deletions of a number of bases that is not a multiple of three; they shift the reading frame, so every codon downstream is misread and the protein is usually destroyed. (3) Chromosomal mutations are large-scale changes: deletions, duplications, inversions and translocations of chromosome segments, and changes in chromosome number (aneuploidy, polyploidy). Mutations can be caused by errors in DNA replication, by radiation, or by chemicals (mutagens), and most are harmful or neutral; a few are beneficial and provide the raw material for evolution. Example — sickle-cell anaemia: a single point mutation (a missense mutation) in the beta-globin gene changes the sixth codon from GAG (glutamic acid) to GTG (valine); the altered haemoglobin (HbS) forms fibres when oxygen is low, distorting red blood cells into a sickle shape, which blocks capillaries and breaks down easily. People with two copies of the allele develop sickle-cell anaemia, while carriers (one copy) are protected against malaria — an example of a mutation that is harmful in one form and advantageous in another.
Reference: VU handout — Mutation; source of variation; heredity and variation.

Q5. What is pleiotropy, and how does the environment influence gene expression? Give examples of each.
Answer: Pleiotropy is the phenomenon in which one gene affects two or more apparently unrelated traits, because the gene's product is used in more than one pathway or tissue. Example: the allele for sickle-cell anaemia affects not only the shape of red blood cells but also the spleen, lungs, kidneys and resistance to malaria — many symptoms from one gene. Another example is phenylketonuria (PKU): a single defective enzyme gene causes mental retardation, light skin and a musty body odour. Pleiotropy shows that genes do not act one-to-one on traits; the relationship between genotype and phenotype is many-to-many. The environment also influences how genes are expressed — the phenotype is the result of genotype plus environment. Examples: (1) The Himalayan rabbit carries a temperature-sensitive allele for pigment production: the enzyme works only in cooler parts of the body, so the ears, nose and feet (which are cooler) are dark while the warm body is white; shaving a warm patch and keeping it cool makes dark fur grow there. (2) Human height is strongly affected by nutrition: people with the same genetic potential grow taller with a good diet. (3) In plants, the same genotype can produce very different growth forms in sun or shade. (4) In PKU, the harmful effects of the genotype can be prevented by an environmental change — a low-phenylalanine diet in childhood. So a gene sets a range of possible outcomes, and the environment decides where in that range the organism ends up.
Reference: VU handout — Pleiotropy; environmental effects.

FAQ

Q: Is the Midterm from Lectures 1-22?
A: Yes — Midterm covers Lectures 1-22 and Finalterm covers Lectures 23-45.

Q: Does the quiz work from this post?
A: Yes — use the 'Take the quiz' link above; the quiz is already live for this course (Midterm 10 and Finalterm 10).

Q: Are the answers verified?
A: Yes — all 30 items are marked Verified, solved independently and cross-checked against at least two independent sources.

More Solved Papers

See the Solved MCQs page and the midterm and finalterm mega hubs for solved papers for every subject.