Explain Incomplete Dominance Using Snapdragon Flowers as an Example

Explain Incomplete Dominance Using Snapdragon Flowers as an Example

Incomplete dominance: when traits blend

Flower colour in snapdragons

Mendel’s results in crossing peas, blackness vs brown fur color, and eumelanin production vs pheomelanin product all demonstrate traits are inherited as dominant and recessive. This contradicts the historical view that offspring always exhibited a alloy of their parents’ traits. All the same, sometimes heterozygote phenotype is intermediate between the ii parents. For example, in the snapdragon,
Antirrhinum majus
(Figure 20), a cross betwixt a homozygous parent with white flowers (C


) and a homozygous parent with red flowers (C


) will produce offspring with pink flowers (C


) (Figure 21).

Figure 20:
These pink flowers of a heterozygote snapdragon event from incomplete dominance. (credit: “storebukkebruse”/Flickr)

Note that different genotypic abbreviations are used to distinguish these patterns from elementary say-so and recessiveness. The abridgement

  tin can be read as “at the flower color factor (C), the white allele is present.”

Effigy 21:
A cross betwixt a red and white snapdragon will yield 100% pink offspring.

This pattern of inheritance is described as
incomplete dominance, meaning that neither of the alleles is completely dominant over the other: both alleles tin can be seen at the same time. The allele for red flowers is incompletely dominant over the allele for white flowers. Red + white = pink. The results of a cantankerous where the alleles are incompletely dominant can even so be predicted, simply as with complete dominant and recessive crosses.
Figure 22
shows the results from a cross between two heterozygous individuals:



ten C


 The expected offspring would have the genotypic ratio 1




Due west


, and the phenotypic ratio would be 1:2:one for red:pink:white. The basis for the intermediate colour in the heterozygote is simply that the pigment produced by the red allele (anthocyanin) is diluted in the heterozygote and therefore appears pinkish because of the white background of the flower petals.

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Figure 22:
The results of crossing two pink snapdragons.

Straight, curly, and wavy hair in dogs

Figure 23:
The wavy hair on this labradoodle is caused past incomplete dominance. (Credit: Localpups, Flickr)

Another example of incomplete authorization is the inheritance of straight, wavy, and curly pilus in dogs. The KRT71 gene is used to synthesize the keratin 71 protein. Genes in the KRT family provide instructions for making proteins called keratins. Keratins are a group of tough, fibrous proteins that form the structural framework of epithelial cells, which are cells that line the surfaces and cavities of the body. Epithelial cells brand upwardly tissues such equally the hair, pare, and nails. These cells also line the internal organs and are an of import office of many glands.

Keratins are all-time known for providing forcefulness and resilience to cells that course the hair, skin, and nails. These proteins allow tissues to resist damage from friction and minor trauma, such as rubbing and scratching. Keratins are also involved in several other critical cell functions, including prison cell movement (migration), regulation of cell size, cell growth and division (proliferation), wound healing, and ship of materials within cells. Different combinations of keratin proteins are found in unlike tissues.

The mutation which causes curly pilus in dogs, such as the labradoodle seen in Effigy 23, is in exon 2 of the factor and is predicted to essentially disrupt the structure of the keratin 71 protein (Cadieu, 2009). This alter in protein shape prevents the keratin proteins from interacting together correctly within the pilus, altering the structure of the hair and resulting in a curly glaze (Runkel, 2006).

When a dog has two curly alleles (KCKC), it has a very curly coat, such equally on the poodle in
Effigy 24. A dog with two straight alleles (M+G+) has a straight coat. Dogs that are heterozygous (K+KC) have an intermediate or wavy coat like the labradoodle in
Effigy 23.

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Figure 24:
This poodle has two copies of the curly allele of the KRT71 gene (KCGrandC). Compare his curly hair to the wavy pilus of the labradoodle in Figure 23. The labradoodle is heterozygous (K+ThousandC). (Credit B. Schoener; From Wikimedia)

Human being Connexion – Blood Type

Blood is classified into unlike groups according to the presence or absence of molecules called antigens on the surface of every ruby-red blood cell in a person’s body. Antigens determine blood type and can either be proteins or complexes of sugar molecules (polysaccharides). The genes in the blood grouping antigen family provide instructions for making antigen proteins. Blood group antigen proteins serve a multifariousness of functions within the cell membrane of red blood cells. These protein functions include transporting other proteins and molecules into and out of the cell, maintaining cell structure, attaching to other cells and molecules, and participating in chemical reactions.

There are 29 recognized blood groups, virtually involving just one gene. Variations (polymorphisms) within the genes that determine blood group give rise to the dissimilar antigens for a particular blood group protein. For instance, changes in a few Deoxyribonucleic acid edifice blocks (nucleotides) in theABO factor requite rise to the A, B, and O blood types of theABO blood group. The changes that occur in the genes that determine blood group typically affect simply claret type and are not associated with agin health conditions, although exceptions do occur.

The A and B alleles are codominant, which is similar to incomplete dominance in that heterozygotes accept an intermediate phenotype. If both the A and B alleles are present, both will be seen in the phenotype. The O allele is recessive to both A and B.


Photo credit: InvictaHOG, from Wikipedia.


Unless otherwise noted, images on this page are licensed under CC-BY 4.0 by OpenStax.

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Cadieu E, Neff MW, Quignon P, Walsh Grand, Hunt K, Parker HG, Vonholdt BM, Rhue A, Boyko A, Byers A, Wong A, Mosher DS, Elkahloun AG, Spady TC, André C, Lark KG, Cargill M, Bustamante CD, Wayne RK, Ostrander EA. 2009. Coat variation in the domesticdog is governed by variants in three genes.Science. 326(5949):150-3.

Runkel F, Klaften Thou, Koch One thousand, Böhnert V, Büssow H, Fuchs H, Franz T, Hrabé de Angelis M. 2006. Morphologic and molecular label of two novel Krt71 (Krt2-6g) mutations: Krt71rco12 and Krt71rco13.Mamm Genome. 17(12):1172-82.

OpenStax, Biology. OpenStax CNX. May 27, 2016 http://cnx.org/contents/[email protected]:[email protected]/Extensions-of-the-Laws-of-Inhe

“Blood Group Antigens” by Genetics Dwelling Reference: Your Guide to Understanding Genetic Conditions, National Institutes of Health: U.S> National Library of Medicine is in the Public Domain

“Keratins” by Genetics Home Reference: Your Guide to Agreement Genetic Conditions, National Institutes of Health: U.Due south> National Library of Medicine is in the Public Domain

Explain Incomplete Dominance Using Snapdragon Flowers as an Example

Source: https://openoregon.pressbooks.pub/mhccbiology102/chapter/incomplete-dominance-when-traits-blend/