Golden Key Points- Chapter 4 Principles of Inheritance and Variation

Golden Key Points

Mendelian Genetics:
- Traits are controlled by discrete units called genes.
- Each gene has different forms called alleles.
- Principles: dominance, segregation, independent assortment.
- Mendel’s experiments with pea plants demonstrated these principles.
Dihybrid Cross and Independent Assortment:
- Mendel crossed pea plants differing in two traits.
- Resulted in a 9:3:3:1 phenotypic ratio.
- Demonstrated independent assortment of alleles.
Chromosomal Theory of Inheritance:
- Mendel’s work rediscovered in 1900.
- Chromosomes observed during cell division.
- Chromosomes parallel genes’ behavior.
- Sutton and Boveri proposed chromosomal theory.
- Morgan’s experiments in fruit flies confirmed theory.
Polygenic Inheritance:
- Traits controlled by three or more genes.
- Phenotype reflects additive effect of alleles.
- Example: human skin color.
Pleiotropy:
- Single gene influences multiple phenotypic traits.
- Often due to gene’s effect on metabolic pathways.
- Example: phenylketonuria.
Sex Determination:
- Mechanism varies across species.
- Humans have XY sex determination.
- Birds have ZW system.
- Disorders like color blindness are sex-linked.
Mutation:
- Alters DNA sequences, leading to genotype and phenotype changes.
- Point mutations, deletions, insertions, frame-shift mutations.
- Caused by various factors, including mutagens like UV radiation.
Genetic Disorders:
- Mendelian disorders due to single gene mutations.
- Examples: haemophilia, sickle-cell anemia, phenylketonuria.
- Chromosomal disorders due to chromosomal abnormalities.
- Examples: Down’s syndrome, Turner’s syndrome, Klinefelter’s syndrome.
Pedigree Analysis:
- Studies inheritance patterns in families.
- Helps trace the transmission of genetic traits.
- Uses family trees over generations.
- Important tool in human genetics research.