Heredity and Evolution Class 10 Notes, Formulas, Questions | SSC

This chapter starts with heredity: how characters pass from parents to offspring through genes, and how DNA directs protein synthesis with the help of RNA. It then explains mutation as a sudden change in genes. The second half deals with evolution, the evidences that support it, the theories of Darwin and Lamarck, the formation of new species and the story of human evolution.

Summary

Heredity is the passing of biological characters from one generation to the next through genes. Gregor Johann Mendel is called the pioneer of modern genetics. In 1901 Hugo de Vries explained sudden changes through his mutation theory, and in 1902 Walter Sutton saw paired chromosomes in grasshopper cells. In 1944 Oswald Avery, Maclyn McCarty and Colin MacLeod proved that DNA is the genetic material of all living organisms except some viruses. In 1961 Francois Jacob and Jacques Monod gave a model of protein synthesis in bacteria, which helped reveal the genetic code and led to recombinant DNA technology. Genetics helps in diagnosing, treating and preventing hereditary disorders, in producing hybrid plants and animals and in industries that use microbes.

Genes in DNA control the body by getting proteins made through RNA; this DNA to RNA to protein route is called the central dogma. In transcription, mRNA is made using only one strand of DNA as the template; its nucleotide sequence is complementary to that strand, and RNA has uracil in place of thymine. The mRNA moves from the nucleus to the cytoplasm carrying the code for amino acids. Each amino acid is coded by three nucleotides, called a triplet codon. Dr Har Govind Khorana contributed to discovering the triplet codons of the 20 amino acids and shared the Nobel Prize in 1968.

In translation, tRNA brings amino acids according to the codons on mRNA; tRNA carries an anticodon complementary to the codon. With the help of rRNA the amino acids are joined by peptide bonds. The ribosome moves along the mRNA one codon at a time, which is called translocation. Many such chains combine to form complex proteins that control body functions and appearance. A sudden change in a gene, such as a nucleotide changing its position, is a mutation; some are minor while others cause disorders like sickle cell anaemia.

Evolution is the gradual change in living organisms over a very long period, leading to the formation of new species through natural selection. About 3.5 billion years ago there was no life; simple compounds in the ocean are thought to have formed complex ones like proteins and nucleic acids and then primitive cells. The accepted theory of gradual development says the first living material (protoplasm) formed in the ocean, unicellular organisms followed, and slowly larger and more complex organisms evolved.

Evolution is supported by several evidences. Morphological evidences are similarities in external features such as mouth, eyes, nostrils and ear pinnae in animals, or leaf shape and venation in plants. Anatomical evidences show the same bone pattern in the human hand, foreleg of ox, patagium of bat and flipper of whale although their uses differ. Vestigial organs are degenerated, useless organs such as the appendix, coccyx, wisdom teeth, body hair and ear muscles in humans; the appendix is functional in ruminants and ear muscles in monkeys.

Palaeontological evidences come from fossils, the preserved remains or impressions of buried organisms. Carbon dating, developed by Willard Libby (Nobel Prize 1960), finds age from the decay of C-14 and the changing C-14 to C-12 ratio after death. Connecting links show features of two groups: Peripatus links Annelida and Arthropoda, the duck-billed platypus links reptiles and mammals, and the lungfish breathes with lungs though it is a fish. Embryological evidences show that early embryos of different vertebrates are very similar, pointing to a common origin.

Charles Darwin, in his book Origin of Species, proposed natural selection or survival of the fittest: organisms reproduce in large numbers, compete, and only those with useful modifications survive and reproduce, giving rise to new species. Objections were that natural selection is not the only factor, useful and useless modifications were not explained, and slow and sudden changes were not explained. Jean-Baptiste Lamarck proposed use and disuse of organs and inheritance of acquired characters, with examples like the giraffe's neck and the ironsmith's shoulders; this theory was rejected because acquired changes are not passed on.

Speciation is the formation of new species. A species is a group of organisms that can produce fertile offspring by natural reproduction. Genetic variation, along with geographical and reproductive isolation, leads to new species. Human evolution began after the last dinosaurs disappeared about 7 crore years ago, from lemur-like ancestors. The timeline runs through apes, Ramapithecus, Australopithecus, skilled man of genus Homo (about 20 lakh years ago), erect man (about 15 lakh years ago), Neanderthal man and Cro-Magnon man (about 50 thousand years ago), followed by agriculture, writing, modern science and industrial society.

Mind map

From gene to protein

Important definitions

Formulas

Key points to remember

• Mendel is the pioneer of modern genetics.
• Hugo de Vries gave the mutation theory in 1901; Walter Sutton observed paired chromosomes in grasshopper cells in 1902.
• Avery, McCarty and MacLeod (1944) proved that DNA is the genetic material in all organisms except some viruses.
• George Beadle and Edward Tatum gave proof that protein synthesis is controlled through genes.
• Only one strand of DNA is used in transcription.
• Dr Har Govind Khorana shared the 1968 Nobel Prize for work on triplet codons of 20 amino acids.
• rRNA helps join amino acids by peptide bonds.
• Sickle cell anaemia is an example of a disorder caused by mutation.
• Human hand, ox foreleg, bat patagium and whale flipper have similar bones: anatomical evidence.
• Appendix is functional in ruminants; ear pinna muscles are functional in monkeys.
• Carbon dating was developed by Willard Libby, Nobel Prize 1960.
• Peripatus: link between Annelida and Arthropoda; platypus: reptiles and mammals; lungfish: fish with lungs.
• Darwin wrote Origin of Species; Lamarck proposed inheritance of acquired characters.
• Neanderthal man is the first example of wise man; Cro-Magnon man evolved about 50 thousand years ago.

Solved examples

Example 1. An mRNA molecule has 300 nucleotides that are all read as codons. How many amino acids will it code for?

Step 1: One codon = 3 nucleotides. Step 2: Number of codons = 300 / 3 = 100. Step 3: Each codon codes for one amino acid, so the mRNA codes for 100 amino acids.

Example 2. A segment of the DNA template strand reads T A C G G A. Write the mRNA formed by transcription.

Step 1: mRNA is complementary to the template strand. Step 2: Pairing rules for RNA: A pairs with U, T with A, G with C, C with G. Step 3: T to A, A to U, C to G, G to C, G to C, A to U. Answer: A U G C C U.

Example 3. An mRNA codon is A U G. What will be the anticodon on the tRNA that brings its amino acid?

Step 1: The anticodon is complementary to the codon. Step 2: A pairs with U, U with A, G with C. Answer: U A C.

Example 4. Arrange the following in order of their appearance in human evolution: Cro-Magnon man, Ramapithecus, Dryopithecus, Neanderthal man, Australopithecus.

Using the approximate ages given in the textbook: Dryopithecus (about 2.5 crore years ago), Ramapithecus (about 1 crore years ago), Australopithecus (about 40 lakh years ago), Neanderthal man (about 1.5 lakh years ago), Cro-Magnon man (about 50 thousand years ago).

Example 5. Classify each as morphological, anatomical, vestigial or connecting-link evidence: (a) wisdom teeth, (b) flipper of whale and patagium of bat, (c) Peripatus, (d) similar leaf venation in a group of plants.

(a) Wisdom teeth: vestigial organ. (b) Whale flipper and bat patagium: anatomical evidence (similar bones and joints). (c) Peripatus: connecting link between Annelida and Arthropoda. (d) Similar leaf venation: morphological evidence.

Important questions and answers

Q1. Define heredity. Explain the mechanism of hereditary changes.

Heredity is the transfer of biological characters from parents to offspring through genes. Genes are mostly passed on unchanged, so offspring resemble parents. Sometimes a sudden change occurs in a gene, for example a nucleotide changes its position. Such a change is a mutation. Some mutations are minor, others are major and may cause disorders like sickle cell anaemia. Mutations add new variations that can be inherited.

Q2. Explain the process of formation of complex proteins.

DNA makes mRNA by transcription using one strand as template. mRNA carries triplet codons to the cytoplasm. tRNA with matching anticodons brings amino acids (translation). rRNA helps join the amino acids by peptide bonds. The ribosome shifts by one codon at a time (translocation). Many polypeptide chains together form complex proteins.

Q3. Define vestigial organs. Name some in humans and the animals in which they are functional.

Vestigial organs are degenerated or underdeveloped, useless organs. Examples in humans are the appendix, coccyx (tail bone), wisdom teeth, body hair and ear pinna muscles. The appendix is functional in ruminants and the ear pinna muscles are functional in monkeys, which move their ear pinnae.

Q4. Define fossil. Explain the importance of fossils as proof of evolution.

Fossils are preserved remains or impressions of organisms buried in the earth by floods, earthquakes, volcanoes and similar events. Their age can be found by methods like carbon dating. Once fossils are dated, we learn which organisms lived at which period, and they show that vertebrates slowly arose from invertebrates. Hence fossil study is an important part of the study of evolution.

Q5. What is a connecting link? Give examples.

An organism with characters of two different groups is a connecting link. Peripatus has a segmented body, thin cuticle and parapodia-like organs like annelids, but tracheal respiration and an open circulatory system like arthropods. The duck-billed platypus lays eggs like reptiles but has mammary glands and hair like mammals. The lungfish breathes with lungs although it is a fish.

Q6. Write a short note on Darwin's theory of natural selection.

Darwin published his theory in Origin of Species. All organisms reproduce in large numbers and compete fiercely to survive. Only those with modifications helpful in the competition survive; nature selects the fit and the rest perish. The selected organisms reproduce and, over time, form new species. Objections: natural selection is not the only factor, useful and useless modifications were not explained, and slow and sudden changes were not explained. Still, his work is a milestone.

Q7. Write a short note on Lamarckism.

Lamarck said organisms change because of their activity or laziness (use and disuse of organs) and that acquired characters are passed to the next generation. Examples: the long neck of the giraffe from stretching to tall leaves, strong shoulders of the ironsmith, weak wings of ostrich and emu, swimming legs of ducks and swans, legless snakes. It was rejected because acquired changes are repeatedly found not to pass to offspring.

Q8. Give reasons: Geographical and reproductive isolation gradually leads to speciation.

When populations of a species are separated geographically or cannot interbreed, genes no longer mix between them. Each group collects its own genetic variations and adapts to its own conditions. Over many generations the differences become so large that the groups can no longer produce fertile offspring together, and they become separate species.

Q9. Explain with examples the importance of anatomical evidences in evolution.

The human hand, foreleg of ox, patagium of bat and flipper of whale look different and do different jobs. Yet their bones and joints follow the same structure. This similarity shows that these animals probably came from a common ancestor, which supports evolution.

Q10. What is carbon dating?

Living organisms take in carbon while alive; after death intake stops and only decay of radioactive C-14 continues, so the C-14 to C-12 ratio keeps changing (C-12 is not radioactive). Measuring C-14 radioactivity and this ratio gives the time since death. It was developed by Willard Libby and is used in palaeontology and anthropology to date fossils and manuscripts.

Q11. Fill in the blanks: (a) Transfer of information from DNA to mRNA is called ____. (b) The vestigial organ ____ in the human body is a proof of evolution.

(a) Transcription. (b) Appendix.

Q12. Write the evolutionary history of modern man in brief.

Lemur-like ancestors gave rise to monkey-like animals after dinosaurs vanished about 7 crore years ago. Their tail was lost about 4 crore years ago and apes evolved; gibbon and orang-utan in Asia, gorilla and chimpanzee in Africa. About 2 crore years ago some apes began walking erect and using their hands. Ramapithecus was found in North India and East Africa. The skilled man of genus Homo appeared about 20 lakh years ago, erect man about 15 lakh years ago, who discovered fire. Neanderthal man was the first wise man and Cro-Magnon man came about 50 thousand years ago. Agriculture began about 10 thousand years ago and writing about 5000 years ago.

Exam tips

• Learn the scientist, year and discovery pairs (de Vries 1901, Sutton 1902, Avery trio 1944, Jacob and Monod 1961, Khorana 1968, Libby 1960); they are common fill-in-the-blank items.
• In transcription questions remember U replaces T in RNA.
• Keep transcription, translation and translocation distinct: making mRNA, bringing amino acids, ribosome movement.
• For vestigial organ answers, always name the animal in which the organ is functional.
• Draw the bone structure diagram (hand, ox foreleg, bat, whale) when explaining anatomical evidence.

FAQs

Is Lamarck's theory accepted today?

Development or degeneration of organs by use and disuse is accepted, but the inheritance of acquired characters was rejected, so Lamarckism as a whole was disproved.

Which strand of DNA is used to make mRNA?

Only one of the two strands is used as the template, and the mRNA is complementary to it.

Why is Peripatus called a connecting link?

It has annelid features (segmented body, thin cuticle, parapodia-like organs) and arthropod features (tracheal respiration, open circulation).

What is the difference between a codon and an anticodon?

A codon is a triplet of nucleotides on mRNA; an anticodon is the complementary triplet on tRNA.

These notes were prepared with AI help from the Balbharati Science and Technology Part 2 textbook (2026-27) and checked against it.