The Punnet lattice was proposed by the English scientist Pennet to facilitate the solution of practical problems in genetics. When it comes to one feature that is being studied, you can try to create a diagram-drawing or calculate the possible options in your 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 Punnett lattice is a great way to order the solution.
Based on the known laws of genetics, we know that every qualitative trait of any organism is encoded in DNA. The section of its molecule responsible for one such trait is a gene. Since any cell of the body has a double set of chromosomes in its nucleus, 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 another allele of the gene enters each such germ cell. The Punnett lattice captures all possible types of gametes from each parent. They are written over it from one crossing participantand from either side (usually to the left) - from the other. In the cell of the intersection of a column and a row, we will find a combination of the offspring's genes, which will determine how exactly this or that trait will appear in him.
What are they like
The principle of constructing these tables is the same, but in general it is customary to distinguish the following types of Punnett lattices:
- vertical-horizontal;
- oblique.
In this case, the first variant is built like a regular table with columns and rows, and the second one is a rhombus, on the upper side edges of which the designations of possible parental gametes are written. Use of the second type is rare.
Practical application
As already mentioned, the Punnett lattice is used to solve problems. It is a visual graphical method that allows you to calculate the resulting offspring for any number of characters. The principles for solving any problem in genetics 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 be formed in each parental organism. We enter the data into the Punnett lattice, find all possible genotypes of the descendants. From them you can navigate how each of the resulting organisms will look like.
A very simple example: the coat length genes in cats, let's call them G and g. We carry out crossing of a short-haired cat and a long-haired cat. Genelonghair is recessive, which means that it appears only in the homozygous state, that is, our cat can only have the 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 has already given birth to kittens like him from a cat with long hair, then her formula is Gg. Let it be. And here is the simplest lattice:
|
types gametes |
G | g |
| g | Gg | gg |
| g | Gg | gg |
We found that 50% of kittens have long hair, like the father. And the other half of them are short-haired, but carry the genes for long-haired, their genotypes are the same as their mother.
