The fundamental concepts of genotype, phenotype, alleles, and codons are essential for understanding inherited diseases and individual variations in drug responses. So let's dive in to learn them, accompanied by examples.
Genotype: The Genetic Blueprint
At the core of an individual's genetic makeup lies their genotype, which refers to the specific genetic constitution encoded within their DNA. The genotype encompasses the complete set of genes inherited from both parents, comprising alleles inherited at each genetic locus. A locus (or loci (plural)) is the actual location of the gene on a region of a chromosome.
Phenotype: The Observable Traits
While genotype provides the genetic instructions, phenotype represents the observable traits and characteristics exhibited by an individual as a result of their genotype interacting with environmental factors. Phenotypes encompass a wide range of traits, including physical features, biochemical properties, and disease susceptibilities.
For instance, the gene responsible for determining blood type in humans is ABO. This gene has three main alleles: A, B, and O. An individual's genotype at the ABO locus reflects which combination of these alleles they possess, determining their blood type. Humans have 4 phenotypes and 6 genotypes for the blood group.
The four phenotypes are A, B, AB, and O.
Blood group A has two genotypes (IAIA and IAi).
Blood group B has two genotypes (IBIB and IBi).
Blood group AB has one genotype (IAIB).
Blood group O has one genotype (i i)
This ultimately determines the blood group.
Picture: Understanding Blood type and its inheritance from parents.
Alleles:
Alleles are alternative forms of a gene that occupy the same genetic locus on homologous chromosomes. These variants may differ in their DNA sequence, resulting in variations in gene expression or protein function. Alleles can be dominant, recessive, or co-dominant, influencing how they contribute to the phenotype when present in a heterozygous individual.
For instance, in the context of cystic fibrosis, a hereditary disorder affecting the respiratory and digestive systems, mutations in the CFTR gene lead to the production of defective cystic fibrosis transmembrane conductance regulator (CFTR) protein. The most common mutation associated with cystic fibrosis is known as ΔF508, where a deletion of three nucleotides results in the loss of a phenylalanine residue at position 508 of the CFTR protein. Individuals who inherit two copies of the ΔF508 allele (homozygous) typically develop cystic fibrosis, while carriers (heterozygous) may exhibit milder symptoms or remain asymptomatic.
Codons: The Language of Proteins
Codons are sequences of three nucleotides within messenger RNA (mRNA) molecules that specify the incorporation of a particular amino acid into a growing polypeptide chain during protein synthesis. Each codon corresponds to a specific amino acid or serves as a start or stop signal for protein translation. The genetic code, consisting of codons and their corresponding amino acids, provides the blueprint for synthesizing proteins based on the information encoded in DNA.
For example, the codon AUG serves as the start codon, signaling the initiation of protein synthesis, while codons such as UAA, UAG, and UGA function as stop codons, halting translation and releasing the completed polypeptide chain. Mutations affecting codons can alter the amino acid sequence of proteins, potentially leading to changes in protein structure and function with implications for health and disease.
To conclude, genotype, phenotype, alleles, and codons are fundamental concepts in medical genetics that underpin our understanding of inherited traits, and genetic disorders. By deciphering the genetic code, researchers and clinicians can unlock insights into the molecular basis of diseases and develop personalized approaches to diagnosis, treatment, and prevention.
-Written by Sohni Tagore
Comentários