Mendel´s Laws:

 

Mendel´s Laws specifiy themselves upon the genetical outcome of the fur color of a rabbit.

In the year of 1865, the monk Johann Gregor Mendel, discovered the fist laws of genetic distribution by an experiment with peas. From these recorded results, Mendel stated threee fundamental laws of heredity; these laws are now know as "Mendel´s Laws". They are used universally for plants and animals and are based on Mendel´s coined term of "dominanz"; focused on the genes which reoccur in a dominant manner in generations to follow and the "recessive", mirroring the dominant genes. 

Recessive genes are supressed by the dominant genes and therefore, the term "recessive" has the meaning of: not occuring physically.

Recessive genes are represented by small letters (for example with "m" for the recessive mane gene), whereas dominant genes are documented as capital letters (for example with "M" for the dominant mane gene).  

 

Dominant pairs of genes are represented as:

AA or Aa (a dominant gene supresses a recessive gene)

Recessive pairs of genes are represented as:

aa


The Uniformity Rule: 1st Mendellian Law

 

If one crosses two indivuals, which differ in one feature for which they are both homozygous (a same gene from each parent), the descendants of the first generation (F1-Generation, Filial Generation) will show a uniform appearence in this specific feature.  

This rule applies to both the external appearance (phenotype) as well as for the genotype, which is heterozygous for all descendants of this mating.

In dominant-recessive inheritance, according to the Uniformity Rule, all offspring have the same phenotype inherited by the parent with the dominant gene.

Example: In rabbits, the black fur color is dominant over the blue fur color, therefore when one mates a black rabbit with a blue rabbit, all offspring of the F1 generation carry a black and a blue color gene. This concludes into the offspring being heterozygous.

But even though the F1 generation carries both genes, their external appearence is uniform as the black fur color, due to black being the dominant gene over the blue recessive gene.  

 

P = Parents

DD

 

dd

F1 = Offspring

 

Dd

 

 


 

The Splitting Rule: 2nd Mendellian Law

 

If one cross-breeds two individuals, which are both alike as heterozygous, such as the F1 generation of the example above, then the individuals of the F2 generation are not uniform anymore, but split with respect to the characteristic value in external appearance, after a certain number of conditions. Through this process, the feautures of the P generation (parental generation), in this case the black and blue fur color, are viewed again in the F2 generation.  

In dominant-recessive inheritance, a quarter of the individuals in the F2 generation are homozygous with a heredity of two recessive genes and show relevant feauture values in their appearence, for example the blue fur color.

The remaining three-quarters show the same appearance as homozygous indivuals with a heredity of two dominant genes, in this case the blue fur color. These three-quarters on the other hand, are made up of a quarter of homozygous and two-quarters of heterozygous individuals. 

Example: If one mates the F1 generation to the above P generation, in our case the black offspring cross-bred with another, we obtain phenotypically (directed towards the fur color of the rabbit), black and blue colored offspring in the F2 generation through a ratio of 3:1. Thus proves, that the genetic material for the blue fur color, has not been repressed by the dominating black color gene. In contrast however, through genotypical observation, the ratio of the black to the blue color gene would be 1:2:1. This is due to a homozygous black colored rabbit pairing itself with two heterzygous blue colored rabbits through which the dominating black gene asserts itself and lastly concluding with a homozygous blue colored rabbit. 

 

 

P = Parents

 

Dd

 

  Dd  

F1 = Offspring

DD

 

Dd

Dd   dd
 

The Independence Rule: 3rd Mendellian Law

 

If one cross-breeds individuals which, differ in two characteristic, thus these characteristics are inherited independently from one another. The F1 generation is uniform, but in the F2 generation homozygous combinations occur. 

In the Independence Rule, not only one characteristic but the entire genotyoe of various assets through the cross-breeding of homozygous individuals and their offspring, is considered.

The phenotypes in the offspring generation are displayed in a respective ration of 9:3:3:1.

 

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