Introduction to Genetics Module

Study Notes

Genetics is the study of biological heredity and variation
Early theories on hereditary include Preformation, Epigenesis, Lamarckism, Pangenesis, Germplasm, and Mendelism
Key figures in the development of genetic theories include Jan Swammerdam, Caspar F. Wolff, Karl Ernst von Baer, Jean-Baptiste Lamarck, Charles Darwin, August Weismann, and Gregor Mendel

Alleles: different forms of a gene that determine alternate traits
Locus: the position of an allele within a DNA molecule
Dominance: the ability of one allele to express its phenotype at the expense of an alternate allele
Recessiveness: the expression of an allele is masked by an alternate allele
Homozygous: zygotes carrying two units of one allele
Heterozygous: zygotes carrying two different alleles
Phenotype: the visible expression of a trait or characteristic possessed by an organism
Genotype: the type of genes an organism possesses

The segregation of alleles during gamete formation follows the law of probability, known as the Product Rule
This principle is essential in understanding the design of experiments in plant and animal breeding

Recessive alleles can be identified experimentally through a testcross
A cross between an organism with unknown genotype and a homozygous recessive individual can help identify the genotype
The results of such a cross follow a 3:1 ratio, conforming to the law of probability

Understanding the principle of segregation is crucial in designing experiments in plant and animal breeding
A 9:3:3:1 ratio result in experiments suggests that two independent pairs of alleles are involved, with one member of each pair behaving like a dominant over its allele
Dihybrid backcross experiments can help identify genotypes and phenotypes

A cross between homozygous parents that differ in three gene pairs is a combination of three-pair crosses operating together
The number of gametes, genotypes, and phenotypes expected from different numbers of heterozygous pairs of genes can be calculated without going through the Punnett square or the Forked-line
The number of kinds of gametes is a multiple of 2, i.e. 2n
The number of F2 genotypes is a multiple of 3, i.e. 3n
The number of phenotype is 2n when dominance is present