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".

or

The transmission of characters from the parents to their offsprings is called heredity. 

The movement of the ribosome from one end of the mRNA to the other end by the distance of one triplet codon during translation is known as translocation.

A sudden change that occurs in the nucleotide sequence of a gene, causing either a minor or considerable change in the characters of an individual is known as mutation.

Translation is the process by which tRNA having anticodon to the codon on the mRNA, supplies amino acids, as per the message on mRNA.

A sequence of three adjacent nucleotides in mRNA that codes for one amino acid is known as a codon.

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

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

or

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

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

or

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.

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.

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.

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.

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

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 modern version of Darwin’s theory of natural selection, which incorporates genetics as the source of variations, is called Neo-Darwinism.

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.

• 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.

• 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.

• 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.

• Natural selection, proposed by Charles Darwin, explains evolution as a process where organisms with favourable variations survive and reproduce.
• Organisms produce more offspring than can survive, leading to a struggle for existence.
• Individuals with useful variations are better adapted to the environment and are selected by nature (“survival of the fittest”).
• These favourable traits are inherited by successive generations, resulting in gradual evolution and formation of new species.
• Darwin presented this theory in his book On the Origin of Species (1859), which became a landmark in evolutionary biology.

• Jean-Baptiste Lamarck proposed that morphological changes in organisms occur due to their activities or laziness.
• He introduced the principle of use or disuse of organs, leading to development or degeneration of body parts.
• He explained evolution through acquired characters, such as the long neck of giraffes or strong shoulders of blacksmiths.
• These acquired characters, according to Lamarck, are passed on to the next generation.
• Lamarck’s theory was later disproved, as acquired characters are not inherited genetically.

• 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.