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, the schemes are full of strange designations, and it is simply impossible to remember all the combinations. 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 to 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 itself in him.
What are they
The principle of constructing these tables is one and the same, but in general it is customary to single out the following
types of Pennet grilles:
- vertically horizontal;
- inclined.
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.
Practical use
As already mentioned, the Pennet lattice is used to solve problems. It is a visual graphic method that allows you to calculate the resulting offspring for any number of characters. The principles for solving any genetics problem can be formulated as follows: we determine how each gene will be designated. We find out the parental genotypes (combinations of genes), determine which germ cells can form in each parental organism. We enter the data in the Pennet lattice, we find all the possible genotypes of the descendants. According to them, you can navigate how each of the resulting organisms will look like.
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 him and long hairs from her 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.