Intermediate filament proteins are a family of 70+ proteins. The proteins in the

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Intermediate filament proteins are a family of 70+ proteins. The proteins in the family are fibrous proteins that organize into 10 nm diameter intermediate filaments. Members in this family include desmin, vimentin, and GFAP (found in muscle, fibroblasts and endothelium, and astrocytes respectively); neurofilament proteins in neurons; and nuclear lamin proteins, which form part of the nuclear envelope Keratins are the most common intermediate filament proteins. There are more than 57 unique keratin genes in both dogs and humans. They can be subdivided into two types . Type I, or acidic keratins. They are numbered K9-K20, K23-K28, and K31-K40 Type ll or basic keratins. They are numbered K1-K8, K71-74, K81, and K85-K86 There is a second way to categorize keratins: hard or soft. "Hard" keratins are resistant to both chemical and enzymatic breakdown. The most commonly occurring "hard" acidic keratins in hair are K31 and K35. The main "hard" basic keratins found in hair are K71-74, K81, K85-K86 Individual hairs in humans or a dog's coat contain a mixture of 26+ different keratins. The specific type and ratio of hard and soft, or acidic vs. basic keratins, determines how pliable or stiff a particular hair is. Cells that form hairs can vary the ratio of keratins that are secreted depending on where they are located on the body, season, or stage of life. For example, human head hair tends to be much more flexible and softer than beard or moustache hair. Similarly, a dog's whiskers will be stiffer than hair in its coat. The amino acid sequence of the keratins also affects how the keratins pack together In 2009, Cadieu, et al. published a report explaining the genetics of long hair, wiry coats, and curly hair in dogs. Each of these three characteristics is controlled by a single gene. The R locus associated with curly coats contains the KRT71 gene, which codes for keratin 71. Curly-coated dogs are homozygous (r/r) for a 1-nucleotide change from C to T in Exon 2 of K71

Explanation / Answer

Amino acids are the organic compounds which are composed of a carboxylic group, an amino group, a hydrogen atom and a characteristic side chain. All these molecules bonded to a carbon atom. It can serve as monomers of proteins. Proteins are the polymer of the amino acid linked by the peptide bond which is in the native conformation having the minimum energy and high functional activity. Although there are many different amino acids are present in the cells but only 22 different amino acids participate in the synthesis of proteins which are incorporated ribosomically into the proteins. Each amino acid is specified by a distinct codon which is the sequence of the specific nucleotide to specify each amino acid in the protein. Each codon consists of a triplet code. The single change at the nucleotide level may lead to the change in the sequence of amino acid which ultimately leads to the formation of the different product. The effect of a change in a nucleotide sequence can be observed at both the phenotypic as well as genotypic level.

For example, in dogs, the single amino acid change from arginine (R) to tryptophan (W) at 151 positions (R151W) in one protein change the phenotype from straight to curly hair. The expression of genes at the phenotypic level probably decided by the dominance of particular genes at the genotypic level. If the R/R and R/r genotypes are expressed then it shows the straight hairs and slightly wavy hair phenotypes in the dogs respectively. While if the r/r genotype is expressed then it shows the curly hairs phenotype in dogs. This is so because of the incomplete dominance of R over r gene. And this incomplete dominance at the genotypic level may arise due to the change in the nucleotide sequence. This single change in the sequence of a nucleotide leads to the formation of the entirely new protein which encodes the different phenotype.

Moreover, the single change in the sequence of nucleotides substitution from A (adenine) to T (thymine) at the 6th position converts the glutamic acid codon to the valine codon caused the sickle cell anaemia in humans.

The change in single nucleotide substitution in case of sickle cell anaemia and hair coat phenotype in dogs are different. Sickle cell anaemia arises due to the mutation while the hair coat phenotype is an example of incomplete dominance.

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