Cytological bases of independent inheritance

During gametogenesis, different chromosomes, and with them genes, end up in different gametes. Gene A can be in the same gamete as gene B or gene b. With the same probability, gene a can combine with gene B or b.

Diheterozygous individuals with the AaBb genotype form four gamete species in the same amount: AB, Ab, aB, ab.

During fertilization, the gametes of one organism accidentally meet with the gametes of another organism. The free combination of gametes ends with the formation of 16 types of zygotes. It is possible to establish all possible combinations of genes in the resulting zygotes using the Pennet lattice.

The results of crossing hybrid pea plants can be presented as follows:

Cleavage by phenotype:
9 – yellow smooth;
3 – yellow wrinkled;
3 – green smooth;
1 – green wrinkled.

In general, it looks like this:
9 – dominant on both grounds (A_B_);
3 – dominant in the first and recessive in the second (A_bb);
3 – recessive in the first and dominant in the second (aaB_);
1 – recessive on both grounds (aabb).

Splitting by genotype (9 classes):

1AABB: 2AABb: 1AAbb: 2Aabb: 4AaBb: 2AaBB: 1aaBB: 2aaBb: 1aabb.

Such results are possible only if genes are located in different pairs of chromosomes and complete dominance in two pairs of traits is observed.

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