Theorems and Laws [1]
Laws: Law of Segregation
Law of segregation states that, when a pair of allelomorphs are brought together in the hybrid (F1), they remain together in the hybrid without blending but separate complete and pure during gamete formation.
- Each pair of alleles separates during gamete formation, with one going into each gamete.
- No blending occurs; alleles remain pure and distinct.
- Gametes fuse randomly during fertilisation to form a zygote.
Key Points
Key Points: Chromosomal Disorders or Abnormalities
| Chromosomal Disorder | Chromosomal Abnormality | Karyotype | Major Features | Remarks |
|---|---|---|---|---|
| Down’s Syndrome | Extra copy of chromosome 21 (Trisomy 21) | 47, +21 | Short stature, small round head, furrowed tongue, partially open mouth, broad palm with single crease, mental and physical retardation | Most common autosomal aneuploidy |
| Klinefelter’s Syndrome | Extra X chromosome in males | 47, XXY | Masculine body with feminine traits (gynecomastia), underdeveloped testes, sterile | Sex-chromosome aneuploidy |
| Turner’s Syndrome | Absence of one X chromosome | 45, XO | Short stature, rudimentary ovaries, absence of secondary sexual characters, sterile female | Only monosomy compatible with life |
| Aneuploidy | Gain or loss of one or more chromosomes due to non-disjunction | 2n ± 1 | Severe developmental abnormalities | Includes trisomy and monosomy |
| Polyploidy | Increase in whole set of chromosomes due to failure of cytokinesis | 3n, 4n, etc. | Common in plants; increases size and vigor | Rare and usually lethal in animals |
Concepts [11]
- Introduction of Principles of Inheritance and Variation
- Terminology Related to Mendelism
- Mendel's Experiments on Inheritance
- Extensions of Mendelian Genetics (Deviation from Mendelism)
- Intragenic Interactions - Dominance
- Historical Development of Chromosome Theory
- Comparison Between Gene and Chromosome Behaviour
- Mendel's Laws > The Law of Segregation (Law of Purity of Gametes)
- Sex Determination in Some Insects
- Mendelian Genetics
- Chromosomal Disorders or Abnormalities
