What is the concept of a monohybrid cross in genetics?

A monohybrid cross in genetics is a breeding experiment between parental organisms differing in one genetic trait.

In more detail, a monohybrid cross is a method used by geneticists to determine the inheritance pattern of a particular trait between two single organisms. The term 'monohybrid' is derived from 'mono' meaning single, and 'hybrid' meaning mixed breed. Therefore, a monohybrid cross involves parents that are genetically different in one specific trait.

This concept was first introduced by Gregor Mendel, an Austrian monk and botanist, who is often referred to as the father of genetics. Mendel conducted his experiments on pea plants and observed how traits were passed from one generation to the next. He chose to study one trait at a time, such as seed colour or plant height, and this is where the concept of a monohybrid cross originates.

In a monohybrid cross, the parent organisms, known as the P generation, are each homozygous for the trait being studied but have different alleles for that trait. One parent has two dominant alleles, while the other parent has two recessive alleles. The offspring, known as the F1 generation, are all heterozygous, having inherited one dominant and one recessive allele.

When the F1 generation is self-fertilised or cross-fertilised with each other, the resulting F2 generation exhibits a 3:1 ratio of dominant to recessive phenotypes. This is known as Mendel's Law of Segregation, which states that allele pairs separate or segregate during gamete formation, and randomly unite at fertilisation.

A Punnett square is often used to visualise a monohybrid cross and predict the genotypic and phenotypic outcomes of the offspring. This simple diagram helps to show the probability of each possible genotype and phenotype.

In summary, a monohybrid cross is a fundamental concept in genetics that helps us understand how traits are inherited. It provides a basis for studying more complex inheritance patterns and is a key tool in genetic counselling and breeding experiments.