Genetics is the branch of biology that deals with the rules governing the pattern of inheritance of heredity over generations.
What Is Genetics?
Bateson coined the term "genetics," but Mendel is known as the "Father of Genetics," since he performed hybridization experiments on the pea plant. Later, many scientists performed experiments on genetics, but the studies of T.H. Morgan had a significant impact; therefore Morgan is known as the father of experimental genetics.
Mendel: A Brief Biography
Mendel was born in Austria on 22nd July 1822 and graduated in 1843. He then joined a monastery, where he taught science and maths. He went to the University of Vienna for higher studies and stayed there for about two years, from 1852 to 1853, where he was taught mathematical models.
After returning from the university, he rejoined the monastery and performed hybridization experiments on pea plants from 1856 to 1863. From the results, he proposed the rules of inheritance, which were presented in a proceeding in 1865. His laws were overlooked at the time, overshadowed by the discussion around the theory of the Origin of Species proposed by Charles Darwin.
In 1884, Mendel died due to kidney failure. Later, in 1902 (as stated in the source; a separate summary in the source instead gives 1907), de Vries, Correns, and Tschermak rediscovered Mendel's laws, and these came to be called Mendelism.
Based on these developments, Sutton and Boveri proposed the chromosomal theory of inheritance.
Bateson and Punnett performed an experiment on sweet pea, using a purple flower with long anther and a white flower with short anther (as stated in the source).
Genetic Terminology
- Gene: a segment of DNA that determines a specific character, like height, colour, nail size, etc.
- Character: a feature that can be observed or measured. A character is always found in a population and has alternative forms.
- Trait: the alternative form of a character that an individual can possess. The character "height" has two traits, tall and dwarf (short).
- Allele: the alternative form of a gene. A gene always has two alleles, one from the father and one from the mother.
- Dominant allele: the allele that can synthesize protein. It is always expressed and is denoted by a capital letter.
- Recessive allele: the allele that cannot synthesize protein. It is not expressed and is represented by the small form of the letter that represents the dominant allele.
- Homozygous: when both alleles of a gene are of the same kind. It always forms one kind of gamete. (TT) and (tt) are homozygous.
- Heterozygous (hybrid): when the alleles of a gene are of different kinds. (Tt) for height is heterozygous, and it always produces two kinds of gametes, one carrying the dominant allele and the other the recessive allele.
- Cross: the mating between two homozygous parents with contrasting traits. For example, when a tall pea and a dwarf pea breed, it is called a cross.
- Filial generation: the generation obtained after a cross between homozygous parents with contrasting traits. It might be F1, F2, F3, etc.
- Locus: the position of a gene on a chromosome. It is always fixed for a gene.
- Back cross: a cross between the F1 generation and either one of the parents. It is performed to preserve the desired traits.
- Test cross: a cross between F1 and the recessive parent, performed to find out whether a dominant trait is present in the homozygous or the heterozygous state. For example, if we are given a tall plant and asked to find out whether it is homozygous (TT) or heterozygous (Tt), we cross the tall plant with a dwarf plant. When the offspring are all tall, the tall parent is homozygous; when both tall and dwarf offspring appear, the tall parent is heterozygous.
- Phenotype: the appearance of a trait in an individual. Tall and dwarf are phenotypes for height.
- Genotype: the allele combination for a trait. The trait "tall height" can be due to the genotype (TT) or (Tt).
- Selfing: the cross that takes place between members of the same generation.
- Punnett square: the square board on which the results of a cross are presented. It was introduced by R.C. Punnett.