Mendel's Laws of Inheritance: Principles of Genetics
Mendel's Laws of Inheritance
Mendel's Laws are a set of ground rules for the inheritance of characteristics from parent organisms to their offspring. These basic rules of inheritance are the foundation of genetics. The laws are derived from the work of Gregor Mendel, published in 1865 and 1866, though they were largely ignored until their rediscovery in 1900.
The Model Organism: Pisum sativum
Mendel published his experiments with peas in 1865 and 1866. The main advantages of choosing Pisum sativum as a model organism include:
- Low cost
- Short generation time
- High rate of descent
- Diverse varieties within the same species (color, shape, size, etc.)
- Constant differentiating characters
Mendel's 1st Law: Law of Uniformity
This law states that if two pure breeds are crossed for a given character, the descendants of the first generation are all equal to each other in both phenotype and genotype, and equal in phenotype to one parent. While this describes the transmission of characters, it also highlights the expression of dominance versus the non-expression of recessive traits. Consequently, it is sometimes debated as a formal law, though it indicates consistent results when broken down into phenotypes (F).
Mendel's 2nd Law: Law of Segregation
Also known as the law of equitable segregation or disjunction of alleles, this principle states that during gamete formation, each allele of a pair is separated from the other member to determine the genetic constitution of the subsidiary gamete. These possibilities of hybridization are frequently represented using a Punnett square.
Genetic Heterogeneity
This term applies to mutations in genes located on different chromosomes that produce similar expressions in the phenotype (locus heterogeneity) and mutations affecting different parts of the same gene (allelic heterogeneity). This category complicates the etiological study of genetic developmental variants and serves as a fundamental source of genetic diversity.