GENETICS

Definition and Origin of Genetics

  • Definition: Genetics is the science of heredity and variation, focusing on the inherited characteristics and variations among organisms.

  • Origin of the Scientific Principle: The scientific principles of genetics originated in 1900 with the re-discovery of Gregor Johann Mendel's scientific article published in 1886.

  • Key Term: Mendel introduced the term 'factors' to describe the carriers of heredity information, which are now known as genes. The term 'gene' was coined by Johansen in 1909.

Introduction to Genetics

  • What is Genetics?

    • Genetics is defined as the study of heredity (the tendency of offspring to resemble their parents) and variation (the tendency of offspring to vary from their parents).

  • Examples of Heredity and Variation:

    • Rakesh Roshan and his son Hrithik Roshan

    • Mammootty and his son Dulquer Salmaan (Malayalam Film Industry)

Branches of Genetics

  • Genetics is considered a relatively young branch of biological science.

  • The study of genetics began with Gregor Johan Mendel's experiments.

  • Modern Branches of Genetics include:

    • Cytogenetics: The study of chromosomes and cell division.

    • Molecular Genetics: The study of the molecular structure and function of genes.

    • Phylogenetics: The study of evolutionary relationships among biological entities.

    • Developmental Genetics: The study of genetics involved in the development of organisms.

    • Behavioral Genetics: The study of the relationship between genetics and behavior.

Gregor Johann Mendel

  • Biography:

    • Gregor Johann Mendel (1822-1884) was an Austrian monk celebrated as the Father of Modern Genetics.

    • He discovered the basic principles of heredity through experiments conducted in his monastery's garden, focusing on the plant Pisum sativum (Garden Pea).

  • Period of Study: Mendel conducted his studies from 1856 to 1864 and published his findings in 1866 in the report titled Experiments in Plant Hybridization.

  • Legacy: Mendel died unrecognized in 1884, and his work remained obscure for 34 years until its rediscovery.

Rediscovery of Mendel's Work

  • Mendel's work was independently rediscovered in 1900 by three scientists:

    • Carl Corens (Germany)

    • Hugo de Vries (Holland)

    • Erich von Tschermak (Austria)

  • Significance: This led to the establishment of Mendelism or the Mendelian Laws of Inheritance.

Principles of Genetics

  • The genetic principles are defined as:

    • The rules governing biological phenomena of heredity.

    • The transmission of characteristics from parents to offspring.

    • This transmission occurs via biochemical information encoded in DNA, organized in units called genes.

Key Concepts in Genetics

  • Genetics: The term was first coined by William Bateson in 1906. The word originates from Greek 'gen', meaning 'to become'.

Key Genetic Terms

  1. Gene

    • Coined by Johansen in 1909.

    • Definition: A gene is the hereditary determining factor consisting of a continuous segment of DNA.

    • In eukaryotes, genes occupy specific positions on chromosomes called loci.

  2. Allele

    • Also known as allelomorphs.

    • Definition: Alleles are alternate forms of a gene that occupy identical loci on homologous chromosomes, controlling contrasting characters of the same trait.

    • Forms of Alleles:

      • Dominant Allele: Always expresses its trait.

      • Recessive Allele: Expresses only in the absence of a dominant allele.

    • Example: Alleles for flower color can be for purple or white flowers.

  3. Dominant and Recessive Alleles

    • Dominant allele is represented by capital letters and will always express.

    • Recessive allele is represented by lowercase letters and will express only when there is no dominant allele present.

    • Example: For the trait of height,

      • Dominant: Tall (T)

      • Recessive: Dwarf (t)

  4. Genotype and Phenotype

    • Genotype: The genetic makeup (constitution) of an organism, represented as combinations such as TT, Tt, or tt for height.

    • Phenotype: The physical features or appearance of an organism that results from the expression of the genotype and interactions with environmental factors, examples being tall and dwarf plants.