Explore the basic concepts of genetics including genes, chromosomes, DNA, and inheritance patterns.
Introduction to Genetics – Study Notes
| Year | Scientist | Contribution |
|---|---|---|
| 1859 | Charles Darwin | Proposed natural selection; hinted at variation mechanisms. |
| 1865 | Gregor Mendel | Formulated the laws of inheritance using pea plants. |
| 1902 | Walter Sutton & Theodor Boveri | Chromosome theory of inheritance. |
| 1910 | Thomas Hunt Morgan | Demonstrated genes are located on chromosomes (fruit‑fly experiments). |
| 1953 | James Watson & Francis Crick | Described the double‑helix structure of DNA. |
| 1970s | Frederick Sanger | Developed DNA sequencing methods. |
| 2003 | Human Genome Project | Completed the first reference sequence of the human genome. |
| Law | Description | Typical Ratio (Monohybrid Cross) |
|---|---|---|
| Law of Segregation | Two alleles for a trait separate during gamete formation. | 3 : 1 (dominant : recessive) |
| Law of Independent Assortment | Genes for different traits assort independently (if on different chromosomes). | 9 : 3 : 3 : 1 (dihybrid cross) |
| Law of Dominance | Dominant allele masks the effect of a recessive allele in heterozygotes. | — |
Note: Linked genes, incomplete dominance, codominance, and polygenic traits are non‑Mendelian exceptions.
| Pattern | Key Features | Example |
|---|---|---|
| Autosomal Dominant | One copy of mutant allele → phenotype. | Huntington disease |
| Autosomal Recessive | Two copies required for phenotype. | Cystic fibrosis |
| X‑Linked Dominant | Affects both sexes; males often more severe. | Rett syndrome |
| X‑Linked Recessive | Mostly males affected; females carriers. | Hemophilia A |
| Mitochondrial | Maternal inheritance only (mtDNA). | Leber’s hereditary optic neuropathy |
| Polygenic | Many genes contribute additively. | Height, skin color |
| Multifactorial | Genes + environment. | Type |