Introduction to Inheritance

  • Tibetan people thrive at high altitudes (13,000+ feet) with lower oxygen levels (40% less than sea level).

  • They have accumulated genetic mutations over thousands of years, aiding their adaptation to low oxygen.

Mendel’s Laws of Inheritance

  • Key Concepts include:

    • Variations on Mendel’s Laws

    • Chromosomal Basis of Inheritance

    • Sex Chromosomes and Sex-Linked Genes

Historical Background of Genetics

  • Ancient theories of inheritance:

    • Hippocrates suggested "pangenes" carried traits to offspring, incorrect as somatic changes do not influence germ cells.

    • Blending hypothesis (19th century): suggested traits mix in offspring; rejected as it couldn’t explain reappearance of traits.

Gregor Mendel and Pea Plant Experiments

  • Birth of genetics (1860s) through studies of pea plants:

    • Heredity: transmission of traits across generations.

    • Genes are discrete units inherited unchanged over generations.

  • Experimental method:

    • Controlled cross-fertilization by removing stamens to prevent self-fertilization.

    • Hybridization produced F1 generation, then produced F2 generation through self-fertilization of F1.

    • True-breeding lines → P generation, hybrids → F1 generation, their offspring → F2 generation.

Mendel's Key Findings

  • Law of Segregation:

    • Organisms inherit two alleles for each character; alleles segregate during gamete formation.

    • Example: Monohybrid cross between purple (PP) and white (pp) flowers resulted in ¾ purple (dominant) and ¼ white (recessive) in the F2 generation.

  • Genotype definitions:

    • Homozygous: identical alleles (e.g., PP or pp)

    • Heterozygous: different alleles (e.g., Pp)

  • Law of Independent Assortment:

    • Dihybrid cross shows that alleles for different traits segregate independently, producing a 9:3:3:1 ratio in F2.

Linked Genes and Chromosome Theory

  • Linked genes: genes on the same chromosome that tend to be inherited together.

  • Chromosomal theory explains segregation and independent assortment during meiosis.

Sex Chromosomes and Sex-Linked Inheritance

  • Humans have XX (female) and XY (male) chromosomal systems.

  • Males show sex-linked traits more often; e.g. hemophilia, colorblindness — disorders generally linked to the X chromosome.

Genetic Disorders in Humans

  • Disorders can be recessive (e.g., cystic fibrosis, sickle-cell disease) or dominant (e.g., Huntington’s disease, achondroplasia).

  • Many human traits and disorders follow Mendel's principles and involve single genes.

  • Examples include genetic testing and the impact of genetic technologies on inheritance and medical predictions.

Environmental Influence on Genetics

  • Characters often result from heredity and environmental interactions (e.g., skin color).

  • Phenotypes can be affected by both genetic makeup and environmental factors.

Summary of Key Genetic Concepts

  • Mendel's principles continue to form the foundation of genetics.

  • The law of segregation and the law of independent assortment apply to various traits.

  • Extensions of Mendelian genetics include polygenic inheritance and the effects of linked genes.