There is only one of you on this planet – your DNA is unlike anyone else's; it is unique. Even genetically identical twins differ in appearance and behaviour. Many things affect us as humans, including our genotypes and phenotypes. But what are these, and how do they affect us?
Firstly, we will understand the genotype and phenotype psychology definition.
Then, we will explore the difference between genotype and phenotype psychology.
We will also take a look at the relationship between genotype and phenotype.
Then we will look at identical twins and how genotypes and phenotypes can affect them.
Lastly, we will look at genotype and phenotype examples.
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.
In psychology, an example of a phenotype would be how environmental factors such as home life in childhood can affect how people develop and behave in adulthood.
Caspi et al. (2002) found that participants who exhibited more violent behaviour had a dysfunctional MAOA gene and experienced an abusive childhood. Thus, the genotype of the dysfunctional MAOA gene may not have been the sole cause of the violent behaviour but rather the expression of this gene when exposed to violent situations.
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.
Genotype - blood type, height, or disease. Phenotype - weight.
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.
A family may have a genetic predisposition to developing depression or another mental health problem, but they can avoid developing symptoms with treatment or avoiding potential triggers.
It is essential to distinguish between genotype and phenotype:
Their treatment can be tailored to their circumstances.
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
If genotypes and phenotypes are not the same, can they affect each other?
As humans, we encounter different environmental conditions. Our physiological and behavioural responses to these conditions depend on our genetic makeup. Genotypes generally remain constant from one environment to another.
But, when the same genotype is treated in different environments, it could produce a range of phenotypes. These phenotype variations are thanks to the environmental effect on the expression and function of genotypes influencing the trait.
These changes in the expression of genotypes across different environments are referred to as genotype-environment interactions (GEI).
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).
For fraternal twins (dizygotic twins), the genetic makeup may have similarities (as they are siblings, after all) but are not identical.
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.
Coccaro (1997) is an example of these twin studies. Coccaro examined the criminality of groups of monozygotic twins and some dizygotic twins. The Mz twins had around a 50% concordance rate, whereas the Dz twins had approximately a 19% rate. The finding suggests a genetic component to 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.
Genotype and Phenotype - Key takeaways
- A genotype is the chemical makeup or composition of our DNA. Of all DNA.
- The phenotype is the observable expression of these genes.
- Phenotypes are not a direct result of our pre-chosen genotypes. Instead, phenotypes are a culmination of our genotypes and circumstances that are unique to us as individuals.
- Identical twins share the same genotypes and share half of their genomes, just like any other siblings. Since their genomes are identical, they never have the same phenotype despite their phenotypes being similar.
- For fraternal twins, the genetic makeup may have similarities (as they are siblings, after all) but are not identical.
References
- Punnett homobrown x homoblue, Purpy Pupple, wikimediacommons.org, CC-BY-SA-3.0
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