An overview of genetics as the study of heredity and variation in living organisms, including key concepts such as genes, chromosomes, DNA, and the role of genetics in inheritance.
Introduction to Genetics – Study Notes
| Year | Scientist | Contribution |
|---|---|---|
| 1865 | Gregor Mendel | Established the laws of inheritance using pea plants; coined “genes” (later). |
| 1900 | Rediscovery of Mendel | Hugo de Vries, Carl Correns, and Erich von von Tschermak revived Mendel’s work. |
| 1910‑1920 | Thomas Hunt Morgan | Demonstrated that genes reside on chromosomes (fruit‑fly experiments). |
| 1953 | Watson & Crick | Described the double‑helix structure of DNA. |
| 1955‑1960 | Erwin Chargaff & Rosalind Franklin | Provided critical data on DNA composition and structure. |
| 1970s‑1980s | Molecular cloning & PCR | Enabled manipulation and amplification of specific DNA fragments. |
| 2003 | Human Genome Project | Completed the first reference sequence of the human genome. |
| Pattern | Key Features | Example |
|---|---|---|
| Autosomal Dominant | One copy of a dominant allele produces phenotype. | Huntington disease |
| Autosomal Recessive | Two copies of a recessive allele needed. | Cystic fibrosis |
| X‑Linked Dominant | Dominant allele on X chromosome; affects both sexes, more severe in males. | Rett syndrome |
| X‑Linked Recessive | Recessive allele on X chromosome; males express phenotype more often. | Hemophilia A |
| Mitochondrial | Inherited only from the mother; genes in mitochondrial DNA. | Leber hereditary optic neuropathy |
| Polygenic | Many genes contribute additively. | Height, skin color |
| Incomplete Dominance | Heterozygote shows intermediate phenotype. | Pink snapdragon flowers (Rr) |
| Codominance | Both alleles expressed equally. | ABO blood groups (IA IB) |
Law of Segregation
Law of Independent Assortment