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Overview of Genotype

The genotype of an organism defines the hereditary restrictions and potentials from the foetal stage during pregnancy through adulthood. In a simple manner, a genotype definition is given by, the sum of total genes transferred from parents to offspring. Therefore, the genotype of a specific person is their own personal genetic makeup. This genotype is expressed when the information from genes' DNA has utilized to make RNA molecules and proteins.

It is a well-known fact that all individuals are having large amounts of DNA. But not all DNAs are the same, and there is a sequence variation of DNA amongst individuals. But when these particular sequence differences are applied to a single gene, it is known as a genotype. Therefore, a genotype meaning is explained simply as the unique version of the DNA sequence that an organism contains.

Determination of Genotype

Genotyping is the method of elucidating the genotype of an individual with a biological assay. It is otherwise known as a genotypic assay, and the techniques are, DNA fragment analysis, PCR, allele-specific oligonucleotide (ASO) probes, nucleic acid hybridization to DNA microarrays or beads, and DNA sequencing. Several mutual genotyping techniques are such as restriction fragment length polymorphism (RFLP), amplified fragment length polymorphism (AFLP), terminal restriction fragment length polymorphism (t-RFLP), and multiplex ligation-dependent probe amplification (MLPA).

The analysis of DNA fragment can also be used to determine such diseases causing genetic aberrations as microsatellite instability (MSI), loss of heterozygosity (LOH), and trisomy or aneuploidy. LOH and MSI in specific have been associated with cancer cell genotypes for breast, colon, and cervical cancer.

Examples of Genotype

Let's look at a classic example of Genotype, which is eye color.

  • In this particular example, the allele is either blue or brown with one inherited from the mother and the other from the father.

  • A gene encodes the eye color.

  • Considering the figure that is given below, the blue allele is recessive (b), and the brown allele is dominant (B). If the child inherits two different alleles (heterozygous), they will have brown eyes. To have blue eyes for the child, they must be homozygous for the blue eye allele.

The most common chromosomal aneuploidy is the trisomy of chromosome 21, which manifests itself as Down syndrome. Typically, the current technological limitations allow only a fraction of an individual's genotype to be efficiently determined.

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The figure that is represented above shows the Inheritance chart on how an individual may inherit brown or blue eyes depending on the alleles carried by their parents in detail, with the blue eye color allele being recessive and the brown eye color allele being dominant.

A few other examples of Genotype can be listed below.

  • Height

  • Hair color

  • Shoe size

Genotypes in Terms of Blood Types

Let us look at the explanation of Genotype in terms of blood types.

Q. What Are Blood Types?

Ans. When we look at the mirror, we can find certain traits are apparent. The color of our eyes, the dimples on your cheeks, and the shape of your chin are evident to even the casual observer. Other characteristics, however, are a little more hidden. For example, do we know our blood type? Blood types are the categories of blood classified either by the presence or absence of antigens on the red blood cells (RBC) surface. Antigens are the structures that extend off the red blood cell (RBC). While type A blood contains one type of antigen, type B blood has another type. Whereas, AB-type blood contains the antigens both from A and B, while O type blood contains no antigens.

Blood Antigens

Humans possess four basic types of blood, which are, A, B, AB, and O. Blood type is not noticeable overtly and must be learned through a blood test. Due to this reason, many people are unaware of their blood type.


The type of blood is determined by our genes. These genes are the segments of DNA that code for specific traits. Different versions of genes are referred to as alleles. When determining something like blood type, individuals receive one allele from their biological mother and another from their biological father. The genotype is simply the combination of these alleles that creates the gene for blood type. This allele combination is called a genotype. Now let us relate this genotype (allele combination) to the blood types.

Blood type alleles are an interesting mix, and to better understand them, let's look at background information prior to this. The allele for type A blood is a dominant one. In other words, when someone inherited this allele from a parent, he or she will exhibit the antigen of type A. It is true of the same type B allele: if someone inherited the allele of type B from a parent, he or she would have the type B antigen. The allele of type O is recessive, which means, it will be masked or hidden by the alleles of either A or B.

FAQ (Frequently Asked Questions)

1. How do the ABO Alleles Inherit by our Children?

Ans. Every biological parent donates one ABO alleles to their child from their available two alleles. A mother who is with a Type - O blood can only pass an O allele to her daughter or son. A father who is with Type - AB blood could pass either an A or a B allele to his daughter or son. This couple (mother and father) could have children of either blood type A (Type-O from mother and Type-A from father) or blood type B (Type-O from mother and Type-B from father).

Since there exist four different paternal blood types and four different maternal possible blood types, there are 16 different combinations that are to be considered when predicting the children's blood type. If we know the blood type of our father and mother, possible blood types for their children can be identified.

2. How can one Determine or Predict their Genotype?

Ans. We can determine the Genotype by sending a sample DNA test. Until we have done that, all we can do is only a wild guess. Our genotype is not the ethnicity results. It is exactly how our deoxyribonucleic acids are lined up in each chromosome. Also, there are some phenotypes that cannot be any other genotype. Someone who is albino knows they don't have a gene that codes for active melanin.

A Siamese cat always has two genes that can make only melanin at slightly at low body temperatures. These genes are called recessive genes. At least, everyone has a few pretty much dominant genes. Before the DNA test, if someone wanted to know whether an animal was homozygous for a dominant trait, a breeding test was often done. If such an animal was bred with a homozygous animal for the corresponding recessive gene, and all the offspring had the same phenotype, it was safe to assume that the animal was homozygous fairly. If some of the offspring were similar to the homozygous parent, the animal was heterozygous (having both dominant and recessive gene), that works much better with mice and rats than with animals that only produce a few offspring in their lifetime!