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Mendel's Laws
I have heard the word "Mendel's laws" before, but I don't know about them well....

Well, we will teach you!

I'm sure that you will understand them!

Law of Dominance Law of Segregation Law of Independence

Exceptions to Mendel's laws

There are some exceptions to Mendel's law.

I will illustrate them with several examples.

  • Lethal genes
  • Gene which result in the death of the life form that carry them are called lethal ganes. They are called lethal alleles, too. House mice and drosophila have been studied having these genes. To give you an example of house mice and let’s think about it. House mice have the gene Y that make it yellow and the gene y that make it gray. The gene Y is a lethal gene. And when a mouse gets two, the mouse dies. Thus, all the mice of yellow are the genotype of Yy which have both yellow gene and gray gene. In addition, it appears yellow has a death rate or 2 to 1.


  • Suppressor gene
  • A suppressor gene is a gene which suppresses the effects of others genes. It is also called an inhibiting gene or suppressor, too.
    Think about the case of cocoons of silkworm moth. Silkworm moth has the gene Y that make the cocoon yellow. The gene Y is a dominant gene, so by having it, the silkworm moths are generally yellow. But if a suppressor gene I enters, it will become white not yellow, because a suppressor gene puts down the work of the dominant gene Y. The ratio of yellow to white occurs at a 13 : 3 ratio.


  • Incomplete dominance
  • It means that relationship between the dominant inherited tratr and recessive inherited trait is not completely dominant. If we cross alleles, a new, third or middle trait occurs. Snapdragon and four-o'clock are famous as a thing having this gene.
    You give an example as ipomoea purpurea and let’s think it. For this flower, there is a gene R making it red and gene r making it white. If gene R and gene r is crossed, a red flower and a white one then a pink mixture of red and white will be born. This pink flower has gene R and gene r. Because the R gene hasincomplete dominance.


  • Complementary gene
  • Are one of two or more genes that when combined produce traits different from their separate effects. Sweet peas are often seen as an example.
    Then let’s think of the color of sweet peas. There are two kinds of dominant genes, the gene C making origin of pigment, the gene P changing the origin of pigment into pigment. Because the gene C and the gene P is complementary gene, this flower is purple when the gene C and the gene P gather.


  • Conditional gene
  • Conditional gene is the gene which will appear character if a certain gene is. It includes complementary gene in a broad sense.
    I explain with the group of house mouse which is different from the group of house mouse with which I explain lethal gene a little time ago. The house mouse of this group has the kind of gray and black and the white. And when its color is black, the gene C exists alone. If it is gray, conditional gene is the gene C together, and all of the conditions are met. In the case that its color is white, there is not the gene C, so it is impossible that its color comes out with this dye. Also it appears gray with black with white in the ratio of 9 to 3 to 4.


  • Synonymous gene
  • When a trait is det by two or more genes. It is exemplified by the fruit of the shepherd's purse and the variety of Plantain leaf shapes. I explain it with the form of the fruit of the shepherd's purse. There are T1 and T2 which decide the form of the fruit of the shepherd's purse. These two genes have same function which changes the shape or the form, and they are synonymous gene. So Even if T2 coexists with T1, the form of the fruit becomes the round fan type.

    Dr. Merdel

  • Suppressor Gene
  • It means the gene which suppress the work of more than one allele.
    Consider the Pumpkin. There dominant gene Y gives Pumpkins a yellow color while the recessive y gene makes them green. But if a suppressor gene exists, the pumpkin will become white. Because the gene cancels the function of both the gene Y and the gene y. By the way, it appears white with yellow with green in the ratio of 12 to 3 to 1.


    There are many exceptions, aren't there?

    Laboratory Pond Experimental Room Park Library Forest
    About Heredity What Is a Guppy? Explanation＆Method Quiz What We Want to Tell You  
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    Mendel’s Laws