Among other things, Mendel provided Biology with two very important tools: the laws of inheritance and a set of methods to determine inheritance.
Those laws state that we can predict the outcome of a progeny by defining the distribution of relevant genes in the sex cells (gametes). Thus it is stated that
- hereditary factors (genes) are what is inherited, not the traits that they determine;
- genes are present in pairs at least in the zygote (egg) and will segregate after meiosis, such that half of the resulting haploid cells bear one of the genes of each pair, and only one;
- genes from different pairs may segregate independently, such that they combine randomly in the products of meiosis.
Those methods, applied in a suitable species, involve:
- The production of pure lines (homozygotes) to start a genetic analysis experiment;
- The precise control of every mating/pollination, such that each generation to be analysed, be from a cross or from selfing, is produced homogeneously;
- The extension of the experiment at least to the second generation (F2) after the initial cross to enable the application of the laws of inheritance.
Mendel's great contribution was in the concept of genetic inheritance. Knowing that traits are hereditary has helped farmers, and every type of animal breeder. In addition, people can now learn what diseases, etc. they may pass on to their young or what genetic conditions to which they may be susceptible. For instance, if one's father has hemophilia, a person can go to a genetics clinic and learn if his/her offspring could have the same disease.
It showed that traits were hereditary, and that there are genes that are dominant over the others, while others are recessive and only show up when 2 recessives are together.