Fundamental Principles of Genetics and Evolution

Genetics: Basic Concepts

• Locus: The position of a gene on a chromosome.
• Alleles: Alternative forms that a single gene can have.
• Homozygote: An individual who possesses two identical alleles for a specific character.
• Heterozygote: An individual who possesses two different alleles for a specific character.
• Genotype: The set of genes belonging to an organism.
• Phenotype: The observable characters within an organism's body.

Mendel's Laws

1. 1st Law: Law of Uniformity. In the crossing of two pure lines, the resulting offspring are identical to each other.
2. 2nd Law: Law of Segregation. When crossing the F1 hybrids obtained previously, the two alleles for a character separate during the formation of gametes.
3. 3rd Law: Law of Independent Assortment. Alleles for different characters are inherited independently and combine randomly in the offspring.

Types of Inheritance

• Dominant: Occurs when a dominant allele prevents or locks the expression of a recessive allele in the phenotype.
• Intermediate: When both alleles express their information equally.
• Codominant: When both traits from heterozygous parents are expressed.

Theories on the Origin of Life and Evolution

Hypotheses on the Origin of Life

• Spontaneous Generation: The idea that life arises spontaneously from inert matter.
• Prebiotic Synthesis Theory: The proposal that life on Earth originated from organic matter.

Theories on the Origin of Living Beings

• Fixism: The belief that species remain unchanged since they were first created.
• Evolutionary Theory: The concept that species change over time.

Lamarckism

Lamarck proposed the first evolutionary theory, suggesting that organisms tend toward greater complexity. He argued that the use or disuse of an organ creates or modifies its function, and these acquired characters are inherited.

Darwinism

Darwinism posits that natural selection is the mechanism by which species evolve. All organisms produce more offspring than can survive, and since resources are limited, a struggle for survival occurs. Because variability exists within a population, the environment selects the best-adapted individuals.

Neo-Darwinism

This theory integrates evolution with new data from genetics and other biological disciplines. It establishes that the population, rather than the individual, is the evolutionary unit. Evolution is driven by the genetic variability of individuals, which arises from mutations and recombination.

Origin of Biodiversity

• Species: A set of organisms capable of interbreeding with one another to produce fertile offspring.
• Speciation: The process by which a set of new species originates.