Revision: Heredity and Evolution Science and Technology 2 SSC (English Medium) 10th Standard Maharashtra State Board

The term heredity may be defined as "transmission of genetically based characteristics from parents to offspring".

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A sequence of three nucleotides on mRNA that codes for a specific amino acid is called a triplet codon.

Evolution is a slow and continuous process whereby complex forms of life have emerged from simpler forms through millions of years.

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Mutation is a sudden change in one or more genes, or in the number or in the structure of chromosomes.

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Mutation is a phenomenon which results in an alteration of DNA sequences and consequently results in changes in the genotype and the phenotype of an organism.

Vestigial organs are degenerate organs that are inadequately developed and non-functional. They could be useful in certain related and unrelated species, as well as in ancestors.

Homologous organs are those organs, which are structurally similar but perform different functions.

A species (both singular and plural) is a natural population of individuals or groups of individuals who are similar in all key morphological and reproductive characteristics, allowing them to interbreed freely and produce fertile offspring.

The study of ancient life with the help of fossils is called palaeontology. Fossils are the dead remains of plants and animals that lived in the past in various geological layers.

The evidence of evolution indicated in the given diagram is vestigial organ.

Vestigial organs: Vestigial organs are useless organs that are degenerated or underdeveloped due to non-functionality through several years.

Large number of organisms get buried due to disasters like floods, earthquakes, volcanoes, etc. Remnants and impressions of such organisms remain preserved underground. These are called fossils.

Vestigial organs are those organs that have ceased to be of any use to the possessor but still persist generation after generation in a reduced form. In other words, vestigial organs are the remnants of features that served important functions in the organism's ancestors.

Vestigial organs are reduced and non-functional organs present in an organism that were functional in its ancestors.

Embryology, the study of the development of an organism from egg to adult, also provides evidence for organic evolution.

The origin of new species by gradual modification is called speciation.

The fittest individuals in nature are most likely to reproduce and pass on their good qualities to their offspring. It is called natural selection.

Differences between individuals of the same species that arise naturally and can be passed to offspring are called variations.

The process of formation of a new species from the pre-existing species is called speciation.

According to A.E. Emerson, speciation is the evolutionary process by which new species arise due to genetic divergence and isolation.

Bipedalism is a major type of locomotion that involves movement on two feet instead of four.

• Mendel is the father of modern genetics; he discovered the basic principles of heredity.
• Hugo de Vries (1901) proposed the mutation theory explaining sudden genetic changes.
• Walter Sutton (1902) linked chromosomes with heredity through his study on grasshoppers.
• Avery, McCarty & McLeod (1944) proved DNA is the genetic material in living organisms.
• Jacob & Monod (1961) developed a model of protein synthesis, leading to recombinant DNA technology.

• Transcription is the process by which genetic information from one DNA strand (the template strand) is copied into RNA using RNA polymerase.
• It occurs in the nucleoid in prokaryotes and in the nucleus in eukaryotes; mRNA then moves to the cytoplasm for translation.
• A transcription unit has three parts: promoter (start site), structural gene, and terminator (stop site).
• The process occurs in three stages: initiation (RNA polymerase binds the promoter), elongation (the RNA chain is formed), and termination (RNA polymerase detaches).
• Only one DNA strand acts as a template (3′→5′), while the other is the coding strand (5′→3′).
• In eukaryotes, primary RNA (hnRNA) is processed by capping, tailing, and splicing to form mature mRNA.

• Translation is the process by which the codon sequence on mRNA is decoded with the help of tRNA at the ribosome to form a specific sequence of amino acids in a protein.
• It needs mRNA (template), tRNA (adapter), ribosome (with A, P, and E sites), amino acids, aminoacyl-tRNA synthetase, ATP/GTP for energy, and Mg²⁺ ions.
• Before translation, amino acids are activated and linked to their specific tRNAs (charging) by aminoacyl-tRNA synthetase.
• Initiation: the small ribosomal subunit binds mRNA at the start codon (AUG), the initiator tRNA carrying methionine attaches, and the large subunit joins to form the initiation complex.
• Elongation: amino acids are added one by one through codon–anticodon pairing; peptide bonds form between them, and the ribosome moves forward by one codon at a time (translocation).
• Termination occurs at a stop codon (UAA, UAG, UGA), where release factors free the polypeptide and the ribosomal subunits separate.

• Evolution is the gradual and progressive development of living organisms over a long period due to natural selection.
• Life originated around 3.5 billion years ago from simple inorganic and organic compounds, eventually forming primitive cells.
• The diversity of life on Earth today, from unicellular organisms to complex plants and animals, is a result of continuous evolutionary processes.
• According to the theory of evolution, all complex organisms evolved slowly from unicellular ancestors over 300 crore (3 billion) years.
• Evolution is considered an organizational and multi-dimensional process, reflecting structural and functional advancement in living organisms.

• A mutation is a sudden heritable change in DNA sequences that leads to changes in the genotype and phenotype of an organism.
• Loss of DNA segment = deletion; gain of DNA segment = insertion/duplication; both cause chromosomal aberrations, commonly seen in cancer cells.
• Frame-shift mutation - caused by loss or gain of a DNA segment; Point mutation - change in a single base pair (e.g., sickle cell anaemia).
• Physical mutagens that cause mutation include UV radiation, X-rays, alpha, beta and gamma rays; Chemical mutagens include mustard gas, phenol and formalin.
• Mutation is an important source of genetic variation in organisms, alongside recombination.

• Morphological similarities are observed in body parts of animals (e.g., mouth, eyes, nostrils, ears, hairs).
• In plants, similarities are seen in leaf shape, venation, petiole, etc.
• These structural similarities indicate a common ancestry and evolutionary relationship.

• Structures like human hand, ox foreleg, bat’s patagium, and whale flipper differ in function but have similar bone structure.
• This similarity in bones and joints across different animals suggests a common ancestry.
• Such internal structural similarities serve as strong anatomical evidence for evolution.

• Vestigial organs are degenerate or underdeveloped structures that have lost their original function in certain organisms.
• These organs persist in a degenerate form due to inheritance from ancestral species, despite having little or no current use.
• Examples in animals include splint bones in horse, rudimentary wings in ostrich, vestigial limbs in python, and functionless eyes in burrowing animals.
• Humans possess many vestigial organs such as the appendix, coccyx (tailbone), wisdom teeth, ear muscles, and nipples in males.
• Vestigial organs provide strong evidence for evolution, showing gradual changes in structure and function over time.

• Connecting links are organisms that show features of two different groups, indicating evolutionary relationships.
• Examples include lungfish (link between fishes and amphibians), duck-billed platypus (link between reptiles and mammals), and Peripatus (link between annelids and arthropods).
• These organisms show transitional features, combining traits of both ancestral and descendant groups.
• Connecting links provide strong evidence for evolution, proving continuity and gradual change between major groups of organisms.

• Charles Darwin developed the idea of natural selection based on extensive data collected during his voyage on the HMS Beagle.
• His views on organic evolution were heavily influenced by the essays of Thomas R. Malthus and Charles Lyell.
• Alfred Russel Wallace independently reached the exact same conclusions while studying the fauna of the East Indies, resulting in a joint presentation in 1858.
• Darwin officially detailed his theory in 1859 by publishing his famous book, Origin of Species by Natural Selection.
• He identified variations, the struggle for existence, and heredity as the three chief factors driving the complex process of evolution.

• Organisms evolve by acquiring traits during their lifetime to adapt to environmental changes and passing these traits to their offspring.
• New organs develop in an organism as a direct result of a continuous "new need" created by their environment.
• Continuous use of an organ strengthens and develops it, while continuous disuse leads to its degeneration.
• Lamarck supported this with examples like giraffes developing long necks from stretching and snakes losing limbs from disuse.
• The theory was rejected after Weismann's rat-tail experiments proved that acquired changes only affect body cells and cannot be inherited.

• Speciation is the evolutionary process responsible for the formation of new, distinct species.
• A species is defined as an interbreeding population that shares a specific gene pool and is reproductively isolated from other distinct populations.
• While members within a species exhibit continuous variation, there is a complete discontinuity of variation between different species.
• A species can be divided into geographical races with unique gene frequencies due to environmental differences, yet these races can still interbreed successfully.
• Reproductive isolation, which is the inability of individuals from different populations to interbreed, constitutes the most definitive boundary between different species.

• Origin: human evolution began in the Palaeocene epoch from a tree-dwelling, shrew-like ancestor.
• As forests declined, arboreal mammals were forced to adapt to life on land, an important driving force in human evolution.
• Humans are most closely related to gibbons, chimpanzees, and gorillas.
• Major changes: increase in brain size and cranial capacity, bipedal locomotion, opposable thumb, erect posture, and development of the chin and forehead.
• Functional significance: free forelimbs and opposable thumbs aided tool use, while bipedal locomotion and stereoscopic vision improved movement and survival.
• Early ancestors: Dryopithecus (ape-like) and Ramapithecus (man-like) lived ~15 mya.
• Australopithecines (~2 mya) lived in East African grasslands, hunted with stone tools, but ate mainly fruits.
• Homo habilis - first hominid, brain ~650–800 cc, with little or no meat in diet; Homo erectus (~1.5 mya, Java, brain ~900 cc) probably ate meat.
• Neanderthal man (~1400 cc, 100,000–40,000 years ago) used hides for protection and buried the dead.
• Modern humans: Homo sapiens arose in Africa during the Ice Age, spread worldwide; cave art developed ~18,000 years ago (Bhimbetka, M.P.), and agriculture and settlements began ~10,000 years ago.

• Modern humans (Homo sapiens sapiens) evolved from Cro-Magnons around 50,000 to 11,000 years ago, mainly near the Caspian and Mediterranean regions.
• They have a fully upright posture, binocular vision, a mobile neck, and spinal curves that help with walking and balance.
• Their brain capacity is about 1450–1600 cm³, with a large cerebrum, well-developed forehead and chin, and the ability to speak and think clearly.
• They have proportionate limbs, flat nails, less body hair, and a broad chest, which are all features that support advanced physical and mental tasks.
• Modern humans made metal tools, started agriculture, formed permanent homes, and developed writing, science, and industries, leading to today's civilizations.