Genotype and Phenotype
All organisms are made up of genes or are products of genes. In order to understand fully the concept of genotype and phenotype, it is basic to go down to the meaning of some terms in genetics, this will foster the more comprehensive and easy understanding of genotype and phenotype. We will evidently discuss their relationship and taking a look at why and how we might choose to study them.
Definition of genotype
In terms of biology, a gene can be seen as a section of deoxyribonucleic acid (DNA) that encodes a trait. The arrangement of nucleotides which comprises of a phosphate group, sugar (ribose sugar) and a base in a gene can differ between copies of the same gene. There’s a wide difference between the gene of one person to another. The Genes of identical twins will not also be exact, there must be a difference. These different forms are known as
loci : this refers to the exact position of genes in the chromosome. A diploid organism either inherits two copies of the same allele or one copy of two different alleles from their parents. An individual who inherits two identical alleles, their genotype is said to be homozygous at that locus.
However if it possess two different alleles in the same gene locus, their genotype is referred to as heterozygous for that locus. Alleles of the same gene are either autosomal dominant (RR or Rr) or recessive (RR). Autosomal dominant alleles will always be preferentially expressed (phenotype) over a recessive allele.
The subsequent combination of alleles that an individual possesses for a specific gene is their genotype.
Examples of genotype expression
eye color . Genes encodes for eye color. The allele is either brown, or blue, with one inherited from the mother, and the other inherited from the father.
The brown allele is genetically 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.
Another can be seen in the human genotype for the expression of sickle cell anaemia. When there exist two dominant alleles (AA), The patient is said to be free from the deadly genetic disease. When there is a heterozygous union of alleles (As), the person is known as a carrier. A person with homozygous recessive (ss) is the one that will suffer the genetic disease. He or she is known as the patient of sickle cell anaem
Other examples of genotype include:
Hair color, Height,Shoe size etc.Phenotype is the sum of an organism’s observable characteristics is their phenotype. They are the traits that are expressed. A major difference between phenotype and genotype is that, whilst genotype is inherited from an organism’s parents, the phenotype is the expressed gene.
Whilsta phenotype is influenced the genotype, genotype does not equal phenotype. The phenotype is influenced by the genotype and factors including:
Environmental and lifestyle factors A is an second example of individual’s skin color. Our genes control the amount and type of melanin that we produce, however, exposure to UV light in sunny climates causes the darkening of existing melanin and encourages increased melanogenesis and thus darker skin.
Genotype vs phenotype: Observing the phenotype is simple – we take a look at an organism’s outward features and characteristics, and form conclusions about them. Observing the genotype, however, is a little more complex. It requires biological techniques which it’s principles and steps aren’t simple, especially in interpretation of the results.
Genotyping is the process by which differences in the genotype of an individual are analyzed using biological assays. The data obtained can then be compared against either a second individual’s sequence, or a database of sequences. Most at times, data bases are used, mostly in forensic science; for crime dictation.
Decades ago, genotyping would enable only partial sequences to be obtained. Recently, major technological advances ,state of whole genome sequencing has made it possible for complete sequencing of genomes.
(WGS) allows entire sequences to be obtained. An efficient process that is increasingly affordable, WGS involves using high-throughput sequencing techniques such as single-molecule real-time (SMRT) sequencing to identify the raw sequence of nucleotides constituting an organism’s DNA. It is not the only way to analyze an organism’s genome – a variety of methods are available.
• DNA Microarray
• Allele-specific Oligonucleotide (ASO) Probes
• DNA Hybridization
Understanding the relationship between a genotype and phenotype can be extremely useful in a variety of research areas.
A particularly interesting area is
pharmacogenomics (considering how a drug affects a body) . Genetic variations can occur in liver enzymes required for drug metabolism, such as Cytochrome P450 . Therefore, an individual’s phenotype, i.e. their ability to metabolize a specific drug, may vary depending on which form of the enzyme-encoding gene they possess. For pharmaceutical companies and physicians, this knowledge is key for determining recommended drug dosages across populations. This is the reason for the observed difference in some specific drug bioavailability between the negros and the whites.
Making use of genotyping and phenotyping techniques in tandem (inverted repeated) appear to be better than using genotype tests alone. Enzymes such as nucleases are used in cutting the DNA fragments. In a comparative clinical pharmacogenomics assay, a multiplexing approach identified greater differences in drug metabolism capacity than was predicted by genotyping alone. This has important implications for personalized medicine and highlights the need to be cautious when exclusively relying on genotyping.
How can we study the relationship between genotype and phenotype?
Using animal models such as mice, scientists can genetically modify an organism so that it will exno longer expresses a particular gene. This is known as knockout mice. By comparing the phenotype of this animal to the wild type phenotype (i.e. the phenotype that exists when the gene has not been removed), we can study the role of certain genes in delivering certain phenotypes.
The Mouse Genome Informatics (MGI) initiative has compiled a database of thousands of phenotypes that can be created and studied, and the genes that must be knocked out to produce each specific phenotype.
Genotype vs phenotype
The set of genes in our DNA which are responsible for a particular trait An organism’s observable characteristics and traits
Characterized by Genotyping techniques such as WGS Observing an organism’s outward characteristics
Depends on The gene sequences an organism possesses Genotype, PLUS epigenetics and environmental factors
Inherited? Yes No
Example Genes encoding eye color An individual with brown eyes