How Genotype Influences Traits and Heredity
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.
Genotypes
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.
FAQs on What Is Genotype? Meaning, Examples & Insights
1. What exactly is a genotype in the context of biology?
A genotype is the complete set of genetic material or the specific combination of alleles (versions of a gene) that an organism inherits from its parents. It essentially serves as the genetic blueprint that determines the potential traits and characteristics of that organism. For instance, the genes that code for eye colour or blood type make up a part of your genotype.
2. What are the main types of genotypes based on allele composition?
Genotypes are primarily classified into two main types based on the alleles they contain for a particular gene:
Homozygous: An individual has two identical alleles for a specific gene. This can be either homozygous dominant (e.g., AA), where both alleles are the dominant version, or homozygous recessive (e.g., aa), where both are the recessive version.
Heterozygous: An individual has two different alleles for a gene (e.g., Aa). In this case, the dominant allele's trait is usually the one that is expressed.
3. Can you provide a simple example of genotype using a classic Mendelian trait?
A classic example is the gene for flower colour in pea plants, as studied by Gregor Mendel. Let's say the allele for purple flowers (P) is dominant, and the allele for white flowers (p) is recessive. The possible genotypes for this trait are:
PP: Homozygous dominant, resulting in purple flowers.
Pp: Heterozygous, also resulting in purple flowers because the 'P' allele is dominant.
pp: Homozygous recessive, resulting in white flowers.
4. What is the key difference between a genotype and a phenotype?
The key difference lies in what they describe. The genotype is the inherited genetic code or the set of genes an organism carries (e.g., Pp for flower colour). The phenotype is the observable physical or biochemical characteristic that results from the genotype's expression (e.g., the actual purple flower). Essentially, genotype is the 'instruction', and phenotype is the 'outcome', which can also be influenced by environmental factors.
5. How does a genotype determine a complex human trait like ABO blood type?
The ABO blood type is determined by the combination of three possible alleles: IA, IB, and i. Each person inherits two of these alleles, one from each parent. The resulting genotype determines the phenotype (blood type) as follows:
Genotypes IAIA or IAi result in Type A blood.
Genotypes IBIB or IBi result in Type B blood.
Genotype IAIB results in Type AB blood (an example of codominance).
Genotype ii results in Type O blood.
6. Is it possible for two organisms with different genotypes to have the same phenotype? Why?
Yes, it is possible. This occurs due to the principles of dominance and recessiveness. For example, in pea plants, a plant with a homozygous dominant genotype (PP) and a plant with a heterozygous genotype (Pp) will both have purple flowers. Although their genetic makeup is different, the presence of at least one dominant 'P' allele masks the recessive 'p' allele, leading to the same observable trait, or phenotype.
7. How can a person's specific genotype be determined?
A person's genotype can be precisely determined through genetic testing. This typically involves analysing a DNA sample from blood, saliva, or tissue. Techniques like DNA sequencing and genotyping arrays can identify the specific alleles present for thousands or even millions of genes. While observing an organism's phenotype can provide clues, only a genetic test can confirm the exact genotype, especially in distinguishing between homozygous dominant and heterozygous individuals.
8. Why is understanding the concept of genotype so important in modern biology and medicine?
Understanding genotypes is fundamental for several reasons. It allows us to:
Predict the inheritance patterns of traits and genetic disorders within families.
Diagnose and understand the basis of genetic diseases like cystic fibrosis or sickle cell anaemia.
Develop personalised medicine (pharmacogenomics), where drug treatments are tailored to an individual's genetic makeup for better efficacy and fewer side effects.
Improve crop and livestock breeds in agriculture through selective breeding based on desirable genotypes.
