Genetics is the study of genes, genetic expression, and the way in which organisms inherit genetic traits from their parents. Inheritance and Mendelian genetics describe the ways in which organisms receive these traits from their parents. Gregor Johann Mendel is known as the father of modern genetics for his discoveries of the principles of heredity based on his work with pea plants in the 19th century. He described inheritance as a particulate and established two important laws: the law of segregation and the law of independent assortment. Modern genetics expands Mendel's discoveries; we now know diploid organisms carry two copies of each gene. An individual's genetic makeup is its genotype, while its expressed traits make up its phenotype.
At A Glance
Gregor Mendel, the father of modern genetics, discovered the mechanism of inheritance.
- Mendel used pea plants to learn the genetic basis of inheritance.
Variants of a gene are called alleles, which can be either dominant or recessive. An organism's genotype (its genetic makeup) determines its phenotype (its expressed traits).
- Genetic diversity is increased by independent assortment ( independent inheritance of genes) and crossing over during meiosis.
- Genes that lie close to each other on chromosomes tend to be inherited together.
- Genes do not always follow the patterns Mendel observed.
Incomplete dominance results in a blending of alleles, while codominance results in the expression of both alleles simultaneously.
- Some genes have more than two alleles.
Pleiotropy happens when one gene codes for more than one phenotype.
- Some traits are the result of multiple genes. Traits can be coded for by more than one gene, known as polygenic inheritance, or one gene can activate another gene, known as epistasis.