The Pennet lattice was proposed by the English scientist Pennet to facilitate the solution of practical problems in genetics. When it comes to one feature by which the study is conducted, you can try to create a drawing diagram or calculate the possible options in the mind. But if two or more signs are studied, schemes are full of strange designations, and remembering all combinations is simply impossible. In such circumstances, the Pennet grid is a great way to streamline the solution.
Based on the known laws of genetics, we know that every qualitative attribute of any organism is encoded in DNA. The portion of its molecule responsible for one such trait is the gene. Since any cell in the body has a double set of chromosomes in its core, it turns out that one gene is responsible for one trait, but it is present in two forms. They are called alleles. Knowing that during sexual reproduction, a cell (gamete) contains a set of chromosomes, divided into two, and remembering how these cells are formed in the body, we understand that one or the other allele of a gene gets into each such sex cell. The Pennet Lattice captures all possible gamete types from each parent. They are recorded above it from one crossbreeding participant and from one side (usually on the left) from the other. In the cell at the intersection of the column and the row, we will find a combination of the descendant's genes, which will determine how this or that trait will manifest in him.
What are they
In this case, the first option is constructed like a regular table with columns and rows, and the second is a rhombus, along the upper side edges of which are written the designations of possible parental gametes. The use of the second type is rare.
A very simple example: fur-length genes in cats, we denote them by G and g. We cross-breed a shorthair cat and a long-haired cat. The longhair gene is recessive, which means that it appears only in a homozygous state, that is, our cat can have only gg genotype. But a cat can be either Gg or GG. We cannot say this by appearance (phenotype), but we can conclude that if she had kittens like her and her long-haired cat, then her formula is Gg. Let it be. And here is the simplest lattice:
It turned out that 50% of kittens have long hair, like a father. And the other half of them are short-haired, but carry longhaired genes, their genotypes are the same as those of their mother.
In this example, both organisms have the Bb genotype. They can produce gametes containing the B or b allele (the first means dominance, the second means recession). The probability of a descendant with the genotype BB is 25%, Bb is 50%, bb is 25%.
Phenotypes are obtained in a combination of 3: 1. A classic example is the coloring of rat coat: for example, B is black, b is white. In this case, 75% of the offspring will have black coat (BB or Bb), while only 25% will have white coat (bb).