Mendelian Genetics, DNA/RNA, Heredity and Evolution Explained
Why do children look like their parents, yet never exactly the same? Why are some people colour blind while their parents see normally? And how did millions of different kinds of living things appear on Earth? The answers lie in genetics and evolution. Genetics explains how characters pass from one generation to the next through genes made of DNA, and evolution explains how living things slowly change over long periods of time to form new species.
Genetics and evolution are important parts of the Biology section in SSC CGL, CHSL, MTS, RRB NTPC, Group D, WBCS, WBPSC, State PSC and Defence exams. Questions are asked on Mendel's experiments and laws, monohybrid and dihybrid ratios, dominant and recessive traits, DNA and RNA structure, the genetic code, sex determination, genetic disorders, and the theories of Lamarck, Darwin and de Vries. This guide explains everything in simple language with Punnett squares, diagrams, tables, memory tricks and 20 MCQs with answers.
➤ Father of Genetics: Gregor Johann Mendel · Plant used: Garden pea (Pisum sativum) · 7 pairs of contrasting traits
➤ Mendel's ratios: Monohybrid 3 : 1 (phenotype), 1 : 2 : 1 (genotype) · Dihybrid 9 : 3 : 3 : 1
➤ Mendel's laws: Dominance · Segregation · Independent Assortment
➤ DNA double helix: Watson and Crick (1953) · Base pairs A–T and G–C · RNA has uracil (U) instead of thymine
➤ Central Dogma: DNA → RNA → Protein · Start codon AUG · 64 codons
➤ Sex of a child: Decided by the father's sperm (X → girl, Y → boy)
➤ Evolution: Lamarck – inheritance of acquired characters · Darwin – natural selection (1859) · de Vries – mutation theory
Basic Terms of Genetics
Heredity is the passing of characters (traits) from parents to their offspring. Variation is the difference between individuals of the same species – even brothers and sisters differ in many ways. Genetics is the branch of biology that studies heredity and variation. The word "genetics" was coined by William Bateson in 1905, and the word "gene" by Wilhelm Johannsen in 1909.
| Term | Simple meaning | Example |
|---|---|---|
| Gene | A segment of DNA that controls one trait; the unit of heredity | Gene for height in pea |
| Allele | Different forms of the same gene | T (tall) and t (dwarf) |
| Dominant | Allele that shows its effect even in a single copy | T – tall |
| Recessive | Allele that shows only when two copies are present | t – dwarf (shows only as tt) |
| Homozygous (pure) | Both alleles same | TT or tt |
| Heterozygous (hybrid) | Two different alleles | Tt |
| Genotype | Genetic make-up | TT, Tt, tt |
| Phenotype | Visible character | Tall or dwarf |
| F1, F2 generation | First and second filial (offspring) generations | Children and grandchildren of the parents (P) |
Gregor Mendel and His Pea Plant Experiments
Gregor Johann Mendel (1822–1884) was an Austrian monk who carried out experiments on garden pea plants in the garden of his monastery in Brno (now in the Czech Republic) between 1856 and 1863. He presented his results in 1865 and published them in 1866, but nobody understood their importance at the time. In 1900, three scientists – Hugo de Vries, Carl Correns and Erich von Tschermak – independently rediscovered his work. Mendel is called the Father of Genetics.
Why did Mendel choose the pea plant? It grows quickly and has a short life cycle; it has clear contrasting traits (tall or dwarf, nothing in between); it normally self-pollinates, so pure lines are easy to get; it can also be cross-pollinated by hand; and it produces many seeds, which gives reliable results.
Mendel's Seven Pairs of Contrasting Traits
| Character | Dominant trait | Recessive trait |
|---|---|---|
| Stem height | Tall | Dwarf |
| Flower colour | Violet (purple) | White |
| Flower position | Axial (along the stem) | Terminal (at the tip) |
| Pod shape | Inflated (full) | Constricted |
| Pod colour | Green | Yellow |
| Seed shape | Round | Wrinkled |
| Seed colour | Yellow | Green |
Watch out: Green is dominant for pod colour, but yellow is dominant for seed colour – a favourite trap in exams.
Monohybrid Cross – One Trait at a Time
Mendel crossed a pure tall plant (TT) with a pure dwarf plant (tt). All the F1 plants were tall (Tt) – the dwarf trait seemed to disappear. When he let the F1 plants self-pollinate, the dwarf trait came back in the F2 generation: about 3 tall plants for every 1 dwarf plant. Figure 1 shows how this happens using a Punnett square (a chart devised by Reginald Punnett).
Figure 1: Mendel's monohybrid cross between tall and dwarf pea plants, with the F2 Punnett square
Mendel's Three Laws
| Law | What it says | Shown by |
|---|---|---|
| 1. Law of Dominance | When two different alleles are present, one (dominant) shows its effect and hides the other (recessive) | All F1 plants are tall |
| 2. Law of Segregation ("law of purity of gametes") | The two alleles of a gene separate during gamete formation, so each gamete gets only one allele | Dwarf plants reappear in F2 (3 : 1) |
| 3. Law of Independent Assortment | Alleles of different genes separate independently of one another | Dihybrid cross (9 : 3 : 3 : 1) |
Dihybrid Cross – Two Traits Together
Mendel also crossed plants that differed in two traits at once – pure round-yellow seeds (RRYY) with pure wrinkled-green seeds (rryy). All F1 seeds were round and yellow (RrYy). In F2, he got four types of seeds in the ratio 9 : 3 : 3 : 1, including two new combinations not seen in the parents. This showed that seed shape and seed colour are inherited independently (Figure 2).
Figure 2: The 9 : 3 : 3 : 1 ratio of a dihybrid cross – each box's width is proportional to the number of plants
Test Cross and Exceptions to Mendel
| Type | Meaning | Example and ratio |
|---|---|---|
| Test cross | Crossing an unknown dominant-looking plant with a recessive (tt) plant to find its genotype | Tt × tt → 1 tall : 1 dwarf (if pure TT, all tall) |
| Incomplete dominance | Neither allele is fully dominant; hybrid shows a mixed character | Snapdragon / four o'clock plant: red × white → pink; F2 = 1 red : 2 pink : 1 white |
| Co-dominance | Both alleles show their effect fully | Human blood group AB (both A and B antigens) |
| Multiple alleles | More than two alleles of a gene exist in a population | ABO blood group gene has three alleles: IA, IB, i |
| Linkage | Genes close together on the same chromosome tend to be inherited together | Studied by T.H. Morgan in fruit flies (Drosophila) |
Exam point: Thomas Hunt Morgan used the fruit fly Drosophila melanogaster and proved that genes are located on chromosomes (Chromosomal Theory of Inheritance). He received the Nobel Prize in 1933.
Chromosomes and Sex Determination
Inside the nucleus of every cell, DNA is packed into thread-like structures called chromosomes. Human body cells have 46 chromosomes (23 pairs). Of these, 22 pairs are autosomes and 1 pair is sex chromosomes – XX in females and XY in males. Sperm and egg cells (gametes) have only 23 chromosomes each, so when they join, the baby again gets 46.
A mother's eggs always carry an X chromosome. A father's sperm carry either an X or a Y. So the sex of the child is decided by the father's sperm, and there is an equal (50 : 50) chance of a boy or a girl (Figure 3).
Figure 3: Sex determination in humans – the father's X or Y sperm decides whether the baby is a girl or a boy
Genetic Disorders
| Disorder | Cause | Key feature |
|---|---|---|
| Colour blindness | Recessive gene on the X chromosome (sex-linked) | Cannot tell red from green; far more common in males |
| Haemophilia ("royal disease") | Recessive gene on the X chromosome (sex-linked) | Blood does not clot properly; mostly affects males |
| Sickle-cell anaemia | Recessive gene on an autosome (mutation in the haemoglobin gene) | RBCs become sickle-shaped |
| Thalassemia | Recessive autosomal genes affecting haemoglobin | Severe anaemia; may need regular blood transfusion |
| Down syndrome | Extra copy of chromosome 21 (trisomy 21) – total 47 | Intellectual disability, short stature; described by Langdon Down |
| Turner syndrome | Only one X chromosome (45, XO) | Females; underdeveloped ovaries, short height |
| Klinefelter syndrome | Extra X chromosome in males (47, XXY) | Males; tall, reduced fertility |
Why are sex-linked diseases more common in males? A male has only one X chromosome, so a single faulty recessive gene on it shows its effect. A female has two X chromosomes, so a normal gene on the other X usually hides the faulty one – she becomes a "carrier". A carrier mother can pass the gene to half of her sons.
DNA – The Molecule of Life
DNA (Deoxyribonucleic Acid) is the genetic material in almost all living things. It carries the instructions to build and run the body. DNA was first identified in 1869 by Friedrich Miescher, who called it "nuclein". In 1953, James Watson and Francis Crick proposed its double helix model, using X-ray pictures taken by Rosalind Franklin and Maurice Wilkins. Watson, Crick and Wilkins received the Nobel Prize in 1962.
DNA looks like a twisted ladder. The two sides of the ladder are made of sugar (deoxyribose) and phosphate. The steps (rungs) are made of pairs of nitrogen bases. There are four bases: Adenine (A), Thymine (T), Guanine (G) and Cytosine (C). They always pair in a fixed way – A with T (by 2 hydrogen bonds) and G with C (by 3 hydrogen bonds). This is called complementary base pairing (Figure 4). One unit of sugar + phosphate + base is called a nucleotide.
Figure 4: Structure of DNA – two strands twisted into a double helix, held together by A–T and G–C base pairs
Proof that DNA is the genetic material: Frederick Griffith's experiment on pneumonia bacteria (1928) showed a "transforming principle"; Avery, MacLeod and McCarty (1944) showed this principle is DNA; and Hershey and Chase (1952) confirmed it using viruses that infect bacteria. Meselson and Stahl (1958) proved that DNA copies itself in a semi-conservative way – each new DNA has one old strand and one new strand.
RNA and the Difference Between DNA and RNA
RNA (Ribonucleic Acid) is a helper molecule that carries instructions from DNA and helps make proteins. In some viruses, such as the influenza virus, HIV and the coronavirus that causes COVID-19, RNA itself is the genetic material.
| Feature | DNA | RNA |
|---|---|---|
| Full name | Deoxyribonucleic acid | Ribonucleic acid |
| Strands | Double-stranded (double helix) | Usually single-stranded |
| Sugar | Deoxyribose | Ribose |
| Bases | A, T, G, C | A, U (uracil), G, C |
| Location | Mainly nucleus (also mitochondria and chloroplasts) | Nucleus and cytoplasm |
| Job | Stores genetic information | Carries information and makes proteins |
| Types | – | mRNA (messenger), tRNA (transfer), rRNA (ribosomal) |
The Central Dogma – From Gene to Protein
Francis Crick described the flow of genetic information in 1958 as the Central Dogma: DNA makes RNA, and RNA makes protein. DNA copies itself (replication) before a cell divides. A gene's message is copied into mRNA (transcription) in the nucleus. The mRNA goes to the ribosomes in the cytoplasm, where tRNA brings amino acids and the protein is built (translation). See Figure 5.
Figure 5: The Central Dogma of molecular biology – replication, transcription and translation
The Genetic Code
The order of bases in mRNA is read three at a time. Each group of three bases is called a codon and stands for one amino acid. There are 4 × 4 × 4 = 64 codons. AUG is the start codon (it also codes for methionine), and UAA, UAG and UGA are stop codons. The code is nearly universal – the same codons mean the same amino acids in bacteria, plants and humans. Indian-born scientist Har Gobind Khorana shared the 1968 Nobel Prize in Medicine with Marshall Nirenberg and Robert Holley for helping to crack the genetic code.
Human Genome: The Human Genome Project, completed in 2003, found that human DNA has about 3 billion base pairs and roughly 20,000–25,000 genes. India's Genome India Project, supported by the Department of Biotechnology, has sequenced the genomes of 10,000 Indians to build a reference database for the country's diverse population.
Mutation and DNA Fingerprinting
A mutation is a sudden, permanent change in DNA. It can be caused by mistakes in copying DNA or by radiation and certain chemicals. Mutations create new variations and are the raw material for evolution. DNA fingerprinting, developed by Alec Jeffreys in 1984, identifies a person from DNA patterns that are unique to each individual (except identical twins). It is used in crime investigation and paternity disputes. In India, Dr Lalji Singh is known as the father of DNA fingerprinting, and the Centre for DNA Fingerprinting and Diagnostics (CDFD) is in Hyderabad.
Origin of Life
The Russian scientist A.I. Oparin (1924) and the British scientist J.B.S. Haldane (1929) independently suggested that life began in the oceans of the early Earth from simple chemicals, with energy from lightning and ultraviolet rays – the "primordial soup" theory. In 1953, Stanley Miller and Harold Urey passed electric sparks through a mixture of methane, ammonia, hydrogen and water vapour and obtained amino acids, supporting this idea.
Theories of Evolution
Evolution is the slow, gradual change in living organisms over many generations, leading to new species. Several scientists tried to explain how it happens. Figure 6 shows the main theories in order.
Figure 6: Major theories of evolution in chronological order
Lamarckism – Inheritance of Acquired Characters
The French naturalist Jean-Baptiste Lamarck presented his theory in his book Philosophie Zoologique (1809). He believed that organs used often become stronger and organs not used become weak (use and disuse), and that such changes gained during life are passed on to children. His famous example was the giraffe: ancestors with short necks stretched to reach leaves on tall trees, and their longer necks passed to their young.
Why it was rejected: August Weismann cut off the tails of mice for more than 20 generations, yet every new generation was born with normal tails. Changes in body cells are not passed on; only changes in the germ cells (sperm and egg) are inherited. This is Weismann's Germplasm Theory.
Darwinism – Natural Selection
The English naturalist Charles Darwin travelled around the world on the ship HMS Beagle (1831–1836) and studied plants and animals, especially the finches and tortoises of the Galapagos Islands. Alfred Russel Wallace reached the same idea independently, and their joint papers were presented in 1858. Darwin published On the Origin of Species in 1859. The main points of his theory are:
| Step | Meaning |
|---|---|
| 1. Over-production | Living things produce far more young than can survive |
| 2. Struggle for existence | Individuals compete for food, space and mates |
| 3. Variation | No two individuals are exactly alike |
| 4. Survival of the fittest / Natural selection | Individuals with useful variations survive and reproduce more |
| 5. Origin of new species | Useful variations add up over many generations, forming new species |
Exam point: The phrase "survival of the fittest" was coined by Herbert Spencer, and Darwin later used it. Darwin could not explain how variations arise and pass on – that answer came from genetics. A well-known living example of natural selection is industrial melanism in the peppered moth in England: when soot darkened tree trunks during the Industrial Revolution, dark-coloured moths survived better than light ones because birds could not easily see them.
Mutation Theory and Modern Synthesis
The Dutch botanist Hugo de Vries studied the evening primrose (Oenothera lamarckiana) and proposed in 1901 that new species arise from sudden, large, heritable changes called mutations, not by slow small changes. Today scientists accept the Modern Synthetic Theory (Neo-Darwinism), which combines Darwin's natural selection with Mendelian genetics, mutation, genetic recombination, genetic drift and isolation.
Evidence of Evolution
| Evidence | Meaning | Example |
|---|---|---|
| Homologous organs | Same basic structure and origin, different functions (divergent evolution) | Forelimbs of human, whale, bat and horse |
| Analogous organs | Different structure and origin, same function (convergent evolution) | Wings of a bird and an insect |
| Vestigial organs | Organs that were useful in ancestors but are reduced and useless now | Human appendix, wisdom teeth, tailbone (coccyx), ear muscles |
| Fossils | Remains of ancient organisms preserved in rocks | Horse evolution series; dinosaur fossils |
| Connecting links | Organisms that show features of two groups | Archaeopteryx (link between reptiles and birds); platypus (reptiles and mammals) |
| Embryology | Early embryos of vertebrates look similar | Gill slits in early human, fish and bird embryos |
Human Evolution in Brief
Humans and apes share a common ancestor. The main stages, in order, are: Dryopithecus and Ramapithecus (ape-like ancestors) → Australopithecus (first to walk upright, in Africa) → Homo habilis ("handy man", first stone tools) → Homo erectus (used fire; includes Java Man and Peking Man) → Homo neanderthalensis (Neanderthal man, buried their dead) → Homo sapiens (modern humans). Modern humans first evolved in Africa and spread across the world.
West Bengal Connection
West Bengal has an important place in Indian genetics and evolutionary biology. J.B.S. Haldane, co-author of the Oparin–Haldane theory of the origin of life and a founder of population genetics, moved to India in 1957 and worked at the Indian Statistical Institute, Kolkata. He later became an Indian citizen. The National Institute of Biomedical Genomics (NIBMG) at Kalyani in Nadia district, set up by the Department of Biotechnology in 2010, was India's first institute dedicated to genomics research, and the Bose Institute in Kolkata, founded by Acharya Jagadish Chandra Bose in 1917, continues research in molecular biology.
To learn about India's science and research schemes, read our post on the VAIBHAV Fellowship and the Darbhanga Planetarium's ISRO Space Gallery. For practice, attempt our CSIR NAL MTS Mock Test, and see how species adapt to their habitat in India's grassland and scrubland ecosystems. More notes are in our Science section.
Quick Revision Box – Easy Tricks to Memorise
Trick 1 – Mendel's ratios "3-1, 1-2-1, 9-3-3-1, 1-1"
Monohybrid phenotype 3:1, genotype 1:2:1, dihybrid 9:3:3:1, test cross 1:1.
Trick 2 – Laws in order "D-S-I"
Dominance, Segregation, Independent Assortment – "Do Study Independently".
Trick 3 – Rediscoverers "Very Clever Teachers" (1900)
de Vries, Correns, Tschermak.
Trick 4 – Pod Green, Seed Yellow
Green pod is dominant, but yellow seed is dominant. All "Tall, Violet, Axial, Inflated, Round" are dominant.
Trick 5 – Base pairing "Apple in the Tree, Car in the Garage"
A pairs with T, C pairs with G. In RNA, "Apple Under the tree": A pairs with U.
Trick 6 – Purines "Pure As Gold"
Purines = Adenine and Guanine. Pyrimidines = C, T, U ("CUT the Py").
Trick 7 – Hydrogen bonds "AT-2, GC-3"
A–T has 2 hydrogen bonds and G–C has 3, so G–C pairs are stronger.
Trick 8 – Central Dogma "Rep – Tran – Trans"
Replication (DNA → DNA), Transcription (DNA → RNA), Translation (RNA → protein).
Trick 9 – Codons "AUG starts, U-A-A, U-A-G, U-G-A stop"
"U Are Away, U Are Gone, U Go Away."
Trick 10 – Chromosome disorders "21 Down, XO Turner, XXY Klinefelter"
Down = 47 (extra 21), Turner = 45 (female), Klinefelter = 47 (male).
Trick 11 – Evolution years "Lamarck 09, Darwin 59, de Vries 01"
1809 – Philosophie Zoologique, 1859 – Origin of Species, 1901 – Mutation theory.
Trick 12 – Homologous = Same origin, Analogous = Same job
"HOMologous – HOMe is same; ANAlogous – ANother origin." Human arm and bat wing are homologous; bird wing and insect wing are analogous.
Trick 13 – DNA dates "1869 – 1953 – 1962 – 1968 – 2003"
DNA found (Miescher), double helix (Watson–Crick), their Nobel, Khorana's Nobel, Human Genome completed.
20 MCQs on Genetics, DNA and Evolution
Q1. Who is known as the Father of Genetics?
(a) Charles Darwin
(b) Gregor Mendel
(c) Hugo de Vries
(d) T.H. Morgan
Answer: (b) – Gregor Mendel worked out the basic laws of heredity using pea plants.
Q2. Mendel conducted his experiments on:
(a) Fruit fly
(b) Snapdragon
(c) Garden pea
(d) Evening primrose
Answer: (c) – Mendel used the garden pea (Pisum sativum); Morgan used the fruit fly and de Vries the evening primrose.
Q3. The phenotypic ratio in the F2 generation of a monohybrid cross is:
(a) 3 : 1
(b) 1 : 2 : 1
(c) 9 : 3 : 3 : 1
(d) 1 : 1
Answer: (a) – 3 dominant : 1 recessive; the genotypic ratio is 1 : 2 : 1.
Q4. The F2 phenotypic ratio of a dihybrid cross is:
(a) 3 : 1
(b) 1 : 2 : 1
(c) 1 : 1 : 1 : 1
(d) 9 : 3 : 3 : 1
Answer: (d) – A dihybrid cross gives four phenotypes in the ratio 9 : 3 : 3 : 1.
Q5. Which of Mendel's laws is explained by a dihybrid cross?
(a) Law of Dominance
(b) Law of Independent Assortment
(c) Law of Segregation
(d) Law of Linkage
Answer: (b) – The appearance of new combinations shows that two traits are inherited independently.
Q6. A cross between an F1 hybrid (Tt) and a recessive parent (tt) is called a:
(a) Back cross only
(b) Dihybrid cross
(c) Test cross
(d) Reciprocal cross
Answer: (c) – A test cross with the recessive parent reveals the genotype; Tt × tt gives 1 : 1.
Q7. Pink flowers obtained by crossing red and white snapdragons is an example of:
(a) Incomplete dominance
(b) Co-dominance
(c) Complete dominance
(d) Linkage
Answer: (a) – Neither allele is fully dominant, so the hybrid shows an intermediate colour.
Q8. Blood group AB in humans is an example of:
(a) Incomplete dominance
(b) Recessive inheritance
(c) Sex linkage
(d) Co-dominance
Answer: (d) – Both IA and IB alleles express themselves fully in group AB.
Q9. How many pairs of autosomes are present in a human body cell?
(a) 23
(b) 22
(c) 46
(d) 11
Answer: (b) – Of the 23 pairs, 22 are autosomes and 1 pair is sex chromosomes.
Q10. The sex of a human child is determined by:
(a) The mother's egg
(b) The number of autosomes
(c) The father's sperm
(d) The mother's age
Answer: (c) – The egg always has X; a sperm with X gives a girl and with Y gives a boy.
Q11. Down syndrome is caused by:
(a) Trisomy of chromosome 21
(b) Loss of an X chromosome
(c) An extra Y chromosome
(d) A gene on the X chromosome
Answer: (a) – An extra copy of chromosome 21 gives 47 chromosomes; Turner syndrome is XO.
Q12. Haemophilia and colour blindness are more common in males because:
(a) The genes are on the Y chromosome
(b) Males have only one X chromosome
(c) They are dominant diseases
(d) They are caused by viruses
Answer: (b) – A single recessive gene on the only X chromosome shows its effect in males.
Q13. The double helix model of DNA was proposed by:
(a) Hershey and Chase
(b) Meselson and Stahl
(c) Miller and Urey
(d) Watson and Crick
Answer: (d) – Watson and Crick proposed it in 1953 using Rosalind Franklin's X-ray data.
Q14. Which nitrogen base is found in RNA but not in DNA?
(a) Thymine
(b) Adenine
(c) Uracil
(d) Guanine
Answer: (c) – RNA has uracil in place of thymine; RNA also has ribose sugar instead of deoxyribose.
Q15. In DNA, guanine always pairs with:
(a) Cytosine
(b) Thymine
(c) Adenine
(d) Uracil
Answer: (a) – G pairs with C by three hydrogen bonds; A pairs with T by two.
Q16. The process of making mRNA from a DNA template is called:
(a) Replication
(b) Transcription
(c) Translation
(d) Mutation
Answer: (b) – Transcription makes mRNA; translation uses mRNA to make proteins on ribosomes.
Q17. Which Indian-born scientist shared the 1968 Nobel Prize for work on the genetic code?
(a) C.V. Raman
(b) S. Chandrasekhar
(c) Venkatraman Ramakrishnan
(d) Har Gobind Khorana
Answer: (d) – Khorana shared the prize with Nirenberg and Holley. Ramakrishnan won the 2009 Chemistry Nobel for ribosome structure.
Q18. "Inheritance of acquired characters" was proposed by:
(a) Darwin
(b) Lamarck
(c) Weismann
(d) Wallace
Answer: (b) – Lamarck proposed it in 1809; Weismann's tail-cutting experiment on mice disproved it.
Q19. Wings of a bird and wings of a butterfly are examples of:
(a) Homologous organs
(b) Vestigial organs
(c) Analogous organs
(d) Connecting links
Answer: (c) – They do the same job but have different structure and origin (convergent evolution).
Q20. Archaeopteryx is considered a connecting link between:
(a) Reptiles and birds
(b) Fishes and amphibians
(c) Amphibians and reptiles
(d) Reptiles and mammals
Answer: (a) – It had feathers like birds and teeth, claws and a bony tail like reptiles.
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Conclusion
Mendel's simple experiments with pea plants laid the foundation of genetics, and the discovery of the DNA double helix explained how genes actually work. Genes made of DNA are copied into RNA and translated into proteins, which build and run our bodies. Over long periods, mutations and natural selection change populations and create new species – this is evolution. For exams, remember Mendel's traits, laws and ratios, the differences between DNA and RNA, base pairing, the genetic code, sex determination, chromosomal disorders, and the theories and evidence of evolution. Revise the tricks above and practise the MCQs to score full marks in this topic.
Reference: NCERT Science Class X (Heredity and Evolution); NCERT Biology Class XII (Principles of Inheritance and Variation; Molecular Basis of Inheritance; Evolution).
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Pradip Chakraborty is the founder and editor of CrackGK. Every article is checked against official and trusted sources such as PIB, NCERT and government websites before publishing. Spotted a mistake? Let us know.