How is the equal genetic contribution of male and female parents ensured in the progeny?
In sexually reproducing organisms, each cell has two copies of each chromosome — one inherited from the male parent and one from the female parent. This means that both parents must be contributing equally to the DNA of the progeny.
During the formation of germ cells, each germ cell takes one chromosome from each pair, which may be of either maternal or paternal origin. Thus, each germ cell has only one gene set instead of the normal two copies found in other body cells.
When two germ cells combine during sexual reproduction, they restore the normal number of chromosomes in the progeny. This mechanism ensures equal genetic contribution from both parents and maintains the stability of the DNA of the species.
Explanation
The textbook explains this mechanism through Mendel's experiments. The key points are: (1) All cells have two copies of each chromosome (one from each parent), (2) Germ cells undergo reduction division to have only one chromosome from each pair, (3) Fertilization restores the diploid condition. This ensures both parents contribute equally to the progeny's genetic makeup.