Heredity and Evolution
1. Heredity
- The transmission of characters from parent to their offspring is known as heredity.
- The study of heredity and variations is known as genetics.
- Clones are organisms that are carbon copies of one another.
- Variation in sexually reproducing organisms is caused due to factors like environment, crossing over, recombination of genes, and mutation.
- The first study of inheritance was done by Gregor Mendel on garden pea.
- Paired condition of chromosomes is known as diploid.
- Unpaired condition of chromosomes is known as haploid.
- DNA (Deoxyribo Nucleic Acid) and RNA (Ribo Nucleic Acid) are the genetic materials in all organisms.
2. Mendel’s Laws of Inheritance
- Law of Dominance
- Law of Segregation (Law of purity of gametes)
- Law of Independent Assortment
3. Genotype and Phenotype
- Genotype is the composition of genes present in an organism.
- The characteristic visible in an organism is called its phenotype.
4. F1 and F2 Generation
- Progeny produced by crossing two parents is called F1-generation (First Filial Generation).
- When the first-generation progeny crosses among themselves to produce the second generation, it is called F2-generation (Second Filial Generation).
5. Monohybrid and Dihybrid Cross
- During a Monohybrid Cross, tall pea plants crossed with short pea plants produced only tall plants in F1 generation.
- F2 progeny consisted of both tall and short plants, indicating inherited traits.
- In a Dihybrid Cross, tall plants with round seeds crossed with short plants with wrinkled seeds produced combinations in F2 generation.
6. Role of DNA
DNA is the source of protein synthesis in a cell. The section of DNA providing information for one protein is called a gene.
7. Physical and Chemical Basis of Heredity
Mendel (1866) stated that heredity is controlled by factors called germinal units.
8. Sex Determination
Human chromosomes include 22 pairs of autosomes, and sex is determined by sex chromosomes (XX for women, XY for men).
9. Evolution
Evolution is the sequence of gradual changes in primitive organisms over millions of years, leading to new species.
A. Evidences of Evolution
- Homologous organs
- Analogous organs
- Fossils
B. Theories of Evolution
Jean Baptiste Lamarck proposed the first theory of evolution.
Charles Darwin explained evolution in his book The Origin of Species, introducing the theory of natural selection.
10. Speciation
The process by which new species develop from existing species is known as speciation, influenced by geographical isolation, genetic drift, and variations.
11. Types of Evolution
- Convergent Evolution
- Divergent Evolution
- Parallel Evolution
12. Fossils
Fossils are remains of dead plants or animals from the remote past, including Ammonite, Trilobite, and Dinosaur fossils.
13. Evolution by Stages
Complex organs evolve gradually over generations, such as eyes and bird feathers.
14. Human Evolution
Humans belong to the species Homo sapiens, originating in Africa and migrating across the world.