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Published: Tue, June 13, 2017
World | By Lorena Waters

Punnett chart


The punnett box is a diagram designed by reginald punnett and is used by biologists to determine the likelihood of a product having a particular genotype.
The punnett box allows you to observe every possible combination of A maternal allele with another paternal allele for each gene studied.

There are several types of crosses among which the most important are :

1. Dihybrid Crossing : It is the most complex crossing that can occur when contemplating two or more genes. The Punnett box only works if the genes are independent of each other.
The following example illustrates a dihybrid cross between two heterozygous pea plants. R represents the dominant allele of the form (rounded) while r shows the recessive allele (rough). Y is the dominant allele of color (yellow) when y is the recessive allele (green). If each plant has the Rr Yy genotype and the genes are independent, they can produce four types of gametes with all possible combinations: RY, Ry, rY and ry.After a series of experiments with green and yellow peas, observing how the characteristics of the parents were transmitted in several generations, the botanist Gregor Mendel raised the basic laws of inheritance transmission. During his observations, Mendel found that features or features stored in coded form in genes could correspond to pure homozygous characteristics or hybrid heterozygous characteristics, in the latter case Of a pair of alternative characteristics of which one is dominant (that is, that which is externally manifested in the organism), and the other is recessive, ie it does not manifest externally, but remains in the genetic endowment and can be done Visible in the next generations.
Based on the above Mendel formulated the following laws:

Segregation Law

When paired Or cross organisms (fecundation) that differ in two or more characters, the factors that determine each character are distributed or segregated independently.

Dominance Law / P>

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When you cross individuals who differ only in one character eg seed color (dominant and recessive for this particular character), the first F1 generation will be similar to the parent having the dominant character.

Independent distribution law

When you cross parents with two different characters (eg pure plants ie Homozygotes with the color of the dominant yellow seeds AA and recessive green aa and shape of the dominant smooth seed LL and rugose recessive ll), these characters are transmitted to the offspring independently. In this case we speak of crosses of hybrids.

Creating a punnett box

A table or table with three columns and three rows is created (Punnet box):

In the horizontal black cells, go The alleles or genes contributed by the father (in this example the father has a pair of AA genes for the color of the seed) but each gamete only receives a gene for that character from the father. A for each cell, that is, a gene for the formation of each gamete at the junction.

This is explained according to the law of segregation A pair of genes is segregated (separated) in the formation of gametes. In the black vertical cells are placed the alleles or genes that will contribute The mother to the gametes. The law of segregation is also observed. Then in each cell a single gene is placed:
The white cells correspond to the gametes of the children that will form at the junction where the pair of genes will be restored for each gameto. Example: If they cross Seeds homozygous dominant AA with green seeds homozygous recessive aa, that is that we have the case AA x aa
In the white cells will form the gametes resulting from the crossing or the combination or cross-linking of the genes provided by the father and the Mother for that character (the gene of the first horizontal cell is combined with the gene of the first vertical cell). At this point the pair number of genes in the gametes formed (one from each parent) is restored

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