Photo credit: InvictaHOG, from Wikipedia. The O allele is recessive to both A and B. If both the A and B alleles are present, both will be seen in the phenotype. The A and B alleles are codominant, which is similar to incomplete dominance in that heterozygotes have an intermediate phenotype. The changes that occur in the genes that determine blood group typically affect only blood type and are not associated with adverse health conditions, although exceptions do occur. For example, changes in a few DNA building blocks (nucleotides) in the ABO gene give rise to the A, B, and O blood types of the ABO blood group. Variations (polymorphisms) within the genes that determine blood group give rise to the different antigens for a particular blood group protein. There are 29 recognized blood groups, most involving only one gene. 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. Blood group antigen proteins serve a variety of functions within the cell membrane of red blood cells. The genes in the blood group antigen family provide instructions for making antigen proteins. Antigens determine blood type and can either be proteins or complexes of sugar molecules (polysaccharides).
Dogs that are heterozygous (K +K C) have an intermediate or wavy coat like the labradoodle in Figure 4.īlood is classified into different groups according to the presence or absence of molecules called antigens on the surface of every red blood cell in a person’s body. A dog with two straight alleles (K +K +) has a straight coat. When a dog has two curly alleles (K CK C), it has a very curly coat, such as on the poodle in Figure 5. This change in protein shape prevents the keratin proteins from interacting together correctly within the hair, altering the structure of the hair and resulting in a curly coat (Runkel, 2006). The mutation which causes curly hair in dogs, such as the labradoodle seen in Figure 23, is in exon 2 of the gene and is predicted to substantially disrupt the structure of the keratin 71 protein (Cadieu, 2009). Keratins are also involved in several other critical cell functions, including cell movement (migration), regulation of cell size, cell growth and division (proliferation), wound healing, and transport of materials within cells. Different combinations of keratin proteins are found in different tissues. These proteins allow tissues to resist damage from friction and minor trauma, such as rubbing and scratching.
Keratins are best known for providing strength and resilience to cells that form the hair, skin, and nails. These cells also line the internal organs and are an important part of many glands. Epithelial cells make up tissues such as the hair, skin, and nails.
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. (Credit: Localpups, Flickr)Īnother example of incomplete dominance is the inheritance of straight, wavy, and curly hair 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. Figure 4: The wavy hair on this labradoodle is caused by incomplete dominance.
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