Definitions [8]
Biogenesis is the idea that life arises only from pre-existing life.
Abiogenesis is the concept that living organisms can arise naturally from non-living substances.
Autogenesis is another term for spontaneous generation, meaning self-origin of life from non-living matter.
The concept where only well-adapted individuals survive in the struggle for existence is called survival of the fittest.
The process where organisms with favorable variations survive and reproduce more successfully than others is called natural selection.
The concept where only well-adapted individuals survive in the struggle for existence is called survival of the fittest.
The process where organisms with favorable variations survive and reproduce more successfully than others is called natural selection.
Define isolating mechanism and explain its types with suitable examples.
Isolation is the separation of the members of a single population into sub populations so that genetic integrity of the subpopulation can be maintained. An isolating barrier is any evolved character of the two species that stops them from interbreeding.
Theorems and Laws [1]
- Hardy–Weinberg’s principle states that allele frequencies in a population remain constant from generation to generation in the absence of evolutionary forces.
- The total collection of all alleles in a population is called the gene pool.
- Genetic equilibrium means no change in allele frequencies over time.
- If p is the frequency of dominant allele and q is the frequency of recessive allele, then
p + q = 1. - Genotype frequencies are expressed as:
p² (AA) + 2pq (Aa) + q² (aa) = 1. - Any deviation from Hardy–Weinberg equilibrium indicates that evolution is occurring.
- The principle helps in detecting the role of natural selection and other evolutionary forces.
Key Points
- The origin of life is a unique event; Earth formed about 4.5 billion years ago, and life appeared about 4 billion years ago.
- Special Creation Theory: all organisms were created by a supernatural power; religion-based, no scientific proof.
- Cosmozoic Theory (Panspermia): life came from other planets as spores; not accepted, as it doesn't explain life's origin elsewhere.
- Spontaneous Generation (Abiogenesis): life arose from non-living matter; later disproved.
- Biogenesis: life arises only from pre-existing life; explains continuity but not the first origin.
- Redi (1668): maggots appeared only in the uncovered meat jar, showing they came from fly eggs.
- Spallanzani (1767): sealed boiled broth showed no growth, proving microbes come from air.
- Pasteur (1861): swan-neck flask trapped airborne microbes, conclusively disproving spontaneous generation.
- The geological time-scale represents the entire history of the Earth and helps correlate geological and biological events in proper sequence.
- The Earth’s crust is made of layered rocks, and radioactive dating techniques estimate the age of the Earth to be about 4.5 billion years.
- Earth’s history is divided into five major eras: Archaeozoic, Proterozoic, Palaeozoic, Mesozoic, and Cenozoic.
- Each era is further divided into periods and epochs, marked by changes in climate, plant life, and animal life.
- The time-scale shows the gradual evolution of life, from simple unicellular organisms to complex plants, animals, and humans.
- Major events such as the origin of life, the rise and extinction of dinosaurs, and the evolution of mammals and humans are recorded in the geological time scale.
- Scientists believe Earth is currently entering a sixth mass extinction (Anthropocene), mainly due to human activities causing rapid loss of biodiversity.
