Inheritance: Single Gene Inheritance

Inheritance is a fundamental concept in genetics that refers to the transmission of traits from parents to offspring. This is regulated by genes.
A ‘gene’ is a small section of DNA that codes for a particular sequence of amino acids, which are used to make a specific protein. Each gene is found on a specific location on a chromosome.
Single gene inheritance refers to the inheritance pattern where a trait is controlled by one pair of genes. In this scenario, a child receives one gene from each parent in the pair composing their genetic makeup.
Alleles are variations of the same gene. A dominant allele is always expressed if present, whereas a recessive allele is only expressed if two copies are present (one from each parent).
Genotype is the term used to describe the pair of alleles present in an organism’s DNA for a specific gene.
Phenotype refers to the physical characteristics or traits that are visibly expressed. These characteristics result from an organism’s genotype and environmental influences.
If both alleles of a gene pair are identical (e.g., AA or aa), the individual is said to be ‘homozygous’ for the trait. If the alleles are different (Aa), the individual is ‘heterozygous’.
In single gene inheritance, each parent passes on one allele to their offspring. The combination of these alleles defines the genotype and thus the phenotype of the offspring.
The Punnett square is commonly used as a tool to predict the genotype of offspring from a genetic cross. The phenotype can then be deduced from the genotype following the principles of dominant and recessive alleles.
Mendel’s laws of inheritance, including the law of segregation and the law of independent assortment, are central to the understanding of single gene inheritance. These laws explain how alleles are separated during the formation of sex cells (gametes) and joined together during fertilisation.
The study of single gene inheritance can help to predict the likelihood of offspring inheriting particular traits, including certain genetic disorders.