Heredity and Evolution

1. Heredity

Definition: The passing of traits from parents to their offspring, either through asexual reproduction or sexual reproduction.

Key Concepts:

1. Gene: A segment of DNA that codes for a specific trait.
2. Chromosomes: Thread-like structures located within the nucleus of animal and plant cells. Each chromosome is made of protein and a single molecule of DNA.
3. DNA (Deoxyribonucleic Acid): The hereditary material in humans and almost all other organisms.
4. Alleles: Different forms of a gene. An individual inherits two alleles for each gene, one from each parent.
5. Genotype: The genetic constitution of an individual organism.
6. Phenotype: The physical expression of genes in an individual, e.g., height, eye color.
7. Dominant and Recessive Traits: Dominant traits are expressed if at least one dominant allele is present. Recessive traits are expressed only when two recessive alleles are present.

Mendel’s Laws of Inheritance:

1. Law of Dominance: In a heterozygote, one trait will conceal the presence of another trait for the same characteristic.
2. Law of Segregation: During the formation of gametes, the two alleles responsible for a trait separate from each other. Alleles for a trait are then recombined at fertilization, producing the genotype for the traits of the offspring.
3. Law of Independent Assortment: Alleles for different traits are distributed to sex cells (& offspring) independently of one another.

2. Evolution

Definition: The change in the heritable characteristics of biological populations over successive generations.

Key Concepts:

1. Variation: The differences in characteristics between individuals in a population.
2. Natural Selection: The process whereby organisms better adapted to their environment tend to survive and produce more offspring.
3. Speciation: The formation of new and distinct species in the course of evolution.
4. Genetic Drift: The change in the frequency of an existing gene variant (allele) in a population due to random sampling of organisms.

Theories of Evolution:

1. Lamarck’s Theory of Evolution (Theory of Inheritance of Acquired Characters): Proposed that organisms can pass on traits acquired during their lifetime to their offspring.
2. Darwin’s Theory of Evolution by Natural Selection: Suggested that evolution occurs through the survival of the fittest, where traits that enhance survival and reproduction become more common in successive generations.

Evidence of Evolution:

1. Fossils: Remains or impressions of ancient organisms preserved in rock.
2. Homologous Structures: Structures in different species that are similar due to common ancestry.
3. Analogous Structures: Structures that are similar in function but not in structure and evolutionary origin.
4. Vestigial Structures: Structures that have lost most or all of their ancestral function.
5. Embryology: The study of embryos and their development, showing common stages of development in different organisms.
6. Molecular Evidence: Comparing DNA and protein sequences between different organisms to identify similarities and differences.

Important Terms and Definitions:

1. Artificial Selection: The intentional reproduction of individuals in a population that have desirable traits.
2. Adaptive Radiation: The diversification of a group of organisms into forms filling different ecological niches.
3. Genetic Engineering: The deliberate modification of the characteristics of an organism by manipulating its genetic material.

Key Figures in Heredity and Evolution:

1. Gregor Mendel: Known as the father of genetics for his work on pea plants and the formulation of the laws of inheritance.
2. Charles Darwin: Developed the theory of natural selection and authored "On the Origin of Species".

These notes cover the fundamental concepts and principles of heredity and evolution that are essential for understanding the subject at the Class 10 level.