Genotype and Phenotype

Genotype Definition: Psychology

Firstly, a genotype has much to do with our DNA and the genes that create our individual and unique DNA. More specifically, a genotype is the chemical makeup or composition of our DNA. A genotype identifies the type of alleles related to a trait or many traits (such as eye colour) and is fixed from the moment of conception.

Fig. 1 Do you have freckles because of one of your parents?

Alleles describe versions of a gene. People inherit one allele for each gene from each parent, and we tend to lump the alleles into categories. For example, the gene for eye colour has an allele for blue eye colour and an allele for brown eye colour, depending on what your parents have.

Phenotype Definition: Psychology

A phenotype describes your physical characteristics, such as your eye colour or height, determined by genes and the environment. A phenotype's influence does not stop at visible characteristics; it can also affect your health history, behaviours, and general disposition.

Differences Between Genotype and Phenotype

The genotype is the genetic basis of an organism. It consists of all the genetic information that determines the characteristics of organisms. The phenotype is the observable expression of these genes that are also affected by the environment.

Genotypes are based on genetic makeup, meaning we are bound to have our genotypes already pre-chosen for us. Your parents, grandparents, great-grandparents, and so on are why you have the genotypes you were born with. But how does that affect phenotypes, and how do they differ?

Phenotypes are not a direct result of our pre-chosen genotypes. Instead, phenotypes are a culmination of both our genotypes and the circumstances of our life that are unique to us. You may know this as the nature vs nurture debate, with our genotypes being the nature aspect and the environment and circumstances of our life as the nurture aspect.

It is usually a mixture of genetic factors (genotype) and environmental factors that affect how these genes are expressed (phenotype), leading to behaviour changes.

Understanding the differences between genotype and phenotype can also help us understand inherited traits.

It is essential to distinguish between genotype and phenotype:

• Some people are born with a genetic predisposition to developing mental health problems.

• Some develop them as a product of their environment.

• A combination of both.

The distinction between genotype and phenotype can help doctors use their resources more effectively when it comes to mental health. A patient with a family history of mental health problems may be more likely to suffer from a chemical imbalance in the brain that responds better to medical treatment than therapy.

Conversely, a patient with no known family history of mental health problems and whose mental health problems are a product of their environment may help physicians determine what elements of their environment have affected them and how.

Relationship between Genotype and Phenotype

Genotype and Phenotype: Identical Twins

In twins, do both individuals share the same phenotype and genotype? As discussed earlier, genotypes are our genetic makeup and therefore are already predetermined. In the case of twins, genotypes are often incredibly similar and considered even a complete replication of each other in the case of identical twins (i.e. monozygotic twins).

Identical twins share the same genotypes, and non-identical twins share half of their genomes, just like any other siblings. Although Mz twins' genomes are identical, they never have the same phenotype despite their phenotypes being similar. This is apparent in the fact that close relations can always tell them apart, even though others might not be able to see the subtle differences.

Twin studies allow us to determine how much genotype influences human behaviour. These studies look at groups of twins and their behaviour. Because twins are so genetically similar (100% genetic match for monozygotic twins and 50% for dizygotic twins), these study results allow us to measure and assess the genetic basis of behaviour.

Genotype and Phenotype Examples

There are so many examples of genotypes, but one common one is eye colour.

• A gene encodes our eye colour.

• In this case, the allele is either brown or blue (one inherited from the mother, and the other inherited from the father).

• The brown allele is dominant (B), and the blue allele is recessive (b). If the child inherits two different alleles (heterozygous), then they will have brown eyes. For the child to have blue eyes, they must be homozygous for the blue-eye allele.

Fig. 2 A genotype is our eye colour.

Influences on phenotypes can include nutrition, temperature, humidity and stress. We can easily see this in the animal kingdom. Think of a flamingo. What colour is the flamingo? I am willing to guess that you see a pink flamingo in your mind's eye. But their natural colour is white! The pink colour is caused by pigments in the organism's diet, not a genetic disposition.