Students must go through these JAC Class 10 Science Notes Chapter 9 Heredity and Evolution to get a clear insight into all the important concepts.
JAC Board Class 10 Science Notes Chapter 9 Heredity and Evolution
→ Variation: The differences in the characters or traits shown by the individuals of same species are called variations.
→ Variations arise during the process of reproduction. These variations help the survival of the individuals.
Depending on the nature of variations, different individuals have different kinds of advantages.
→ Heredity: A process of transmission of characters generation after generation is called heredity. It is a process by which parental characters are transmitted to offsprings.
→ Dominant and recessive trait: A trait which expresses itself in the presence of its contrasting trait is termed as dominant trait whereas recessive trait remains unexpressed in presence of dominant one.
→ Trait: It is a distinguishing feature of a person’s character.
- In simple term, trait is the way in which the characters of an organism are expressed.
- Examples : Blond hair, blue eyes, attached earlobes, tallness, etc.
→ Factor: The unit, which is responsible for the heredity or regulating the expressions of a character is called a factor.
- The factors responsible for an expression of a trait are always in a pair.
- The factor as suggested by Mendel, is now known as gene in the modern genetics.
- The factor (gene) is represented by the English alphabet.
→ Gregor Johann Mendel: He conducted a series of experiments on garden pea plant (Pisum sativum) in order to study heredity.
The results of the Mendel’s experiments explain the mechanism of inheritance.
→ Gene : A section of DNA (nucleotide sequence) that provides information for the synthesis of a specific protein is called gene.
→ Sex determination: The phenomenon of determining the sex of an individual of a species is called sex determination.
- There are different strategies e.g., temperature, chromosomes, genes, hormones, etc. responsible for determining the sex in certain animals.
- In certain animals, the sex determination is not genetically determined, e.g., the Snails can change their sex.
- In human beings in each cell there are 22 pairs of autosomes and 1 pair of sex chromosomes. The 23rd pair is either XX as in females or XY as in males.
→ Genetic drift: A change in the frequency of some genes in a population which provides diversity without any survival advantage is called genetic drift.
→ Evolution: A process of slow, gradual and progressive changes by which complex form of organisms are produced from simple form of organisms over a long period of time is called evolution.
→ Charles Darwin conducted various experiments that led him to formulate the theory of natural selection which states that evolution proceeds due to natural selection.
→ Acquired trait: The characteristics of the organisms, which develop as an interaction with the environment and which are not hereditary are called acquired characteristics or traits, e.g., weight loss achieved by dieting.
→ Inherited trait: The characteristic of the organism, that comes into existence by the changes in DNA structure is called an inherited trait, e.g., skin colour, eye colour, colour of flower, height of plant, etc.
→ Speciation: The phenomenon of origin of a new species from the pre-existing one due to reproductive isolation of a part of its population is called speciation.
→ Speciation is caused due to genetic drift, natural selection, geographical and reproductive isolation.
→ Gene flow: The transfer of genes or alleles between inbreeding population of a particular species is called gene flow.
→ Evidences of evolution:
| Homologous Organs | Analogous Organs | Fossils |
| Structurally similar but may be different functionally. | Basically different in structure and appear similar in their look and also in the function. | Organs preserved in the earth crust and obtained therefrom as samples or impressions |
| Example : Forelimbs of wall lizard and forelimbs of human being | Example : Wings of birds and wings of bats | Example : Ammonites, Trilobites |
- Evolution can be studied with the help of living species and fossils.
- Evolutionary relationships are traced in the classification of organisms.
- Organs or features may be adapted to new functions during course of evolution, e.g., feathers have been initially evolved for. warmth and later adopted for flight.
→ Evolution through artificial selection: Farmers have obtained newer varieties of cabbage from the wild variety of cabbage by artificial selection. Cauliflower, Broccoli, Kohlrabi and Kale species are apparently different from their wild ancestral cabbage.
→ Human evolution: Study of the evolution of human beings indicates that all of us belong to a single species Homo sapiens. Our genetic footprints can be traced back to our African roots.