Mendelian Genetics | Mendelian Theory, Principles & Applications

The study of genes and genetic patterns of inheritance in the wide branch of biological science is referred to as genetics. The concept of gene, DNA, chromosomes, etc. had evolved biology into a field of wide research, due to which we now have hybridized crops with better yield, highly advanced technologies in farming, cloning, production of test-tube babies to even investigating a case of potential harm successfully in forensic science.

Many bio wars were blown out due to the growth in the field of genetics. But who started this? Who invented this amazing concept that changed millions of lives? Quite surprisingly the father of genetics title is awarded to a mathematician, Gregor Mendel.

Like many great artists, the work of Gregor Mendel was not appreciated until after his death. He is now called the “Father of Genetics,” but he was remembered as a gentleman who loved flowers and kept extensive records of weather and stars when he died.

Gregor Mendel was born on July 22, 1822, to a poor farming family who lived in a village in Northern Moravia, which is now part of the Czech Republic. His family valued education but had little resources to send him to school, so he struggled to pay for his education.

In his later years, he joined a few Australian monks who loved science and astronomy and spent a few months of his life with him. After learning a lot from them he developed an interest in the field of botany which led him to take further interest in pea plants.

Mendelian Theory of Genetics

In the 1860s, Mendel introduced theories of inheritance, based on his experimental work with pea plants. Before Mendel, most people believed inheritance was due to a blending of parental ‘essences’, much like how mixing blue and yellow paint will produce a green color.

Mendel instead believed that heredity is the result of discrete units of inheritance, and every single unit (or gene) was independent in its actions in an individual’s genome. According to this Mendelian concept, the inheritance of a trait depends on the passing-on of these units.

Read also:  Detection of Cocaine user by Fingerprint testing | Forensic Yard | 2020

For any given trait, an individual inherits one gene from each parent so that the individual has a pairing of two genes. We now understand the alternate forms of these units as ‘alleles’. If the two alleles that form the pair for a trait are identical, then the individual is said to be homozygous and if the two genes are different, then the individual is heterozygous for the trait.

Based on his pea plant studies, Mendel proposed that traits are always controlled by single genes. However, modern studies have revealed that most traits in humans are controlled by multiple genes as well as environmental influences and do not necessarily exhibit a simple Mendelian pattern of inheritance

Conduction of Experiments & Results

Mendel carried out breeding experiments in his monastery’s garden to test inheritance patterns. He selectively cross-bred common pea plants (Pisum sativum) with selected traits over several generations.

After crossing two plants that differed in a single trait (tall stems vs. short stems, round peas vs. wrinkled peas, purple flowers vs. white flowers, etc), Mendel discovered that the next generation, the “F1” (first filial generation), was comprised entirely of individuals exhibiting only one of the traits.

However, when this generation was interbred, its offspring, the “F2” (second filial generation), showed a 3:1 ratio where three individuals had the same trait as one parent and one individual had the other parent’s trait.

Mendel then theorized that genes can be made up of three possible pairings of heredity units, which he called ‘factors’: AA, Aa, and aa.

  • ‘A’ represents the dominant factor.
  • ‘a’ represents the recessive factor.

In Mendel’s crosses, the starting plants were homozygous AA or aa, the F1 generation was Aa, and the F2 generation was AA, Aa, or aa. The interaction between these two determines the physical trait that is visible to us.

Mendel’s Law of Dominance predicts this interaction; it states that when mating occurs between two organisms of different traits, each offspring exhibits the trait of one parent only. If the dominant factor is present in an individual, the dominant trait will result. The recessive trait will only result if both factors are recessive.

Read also:  Decipherment/Examination of Charred documents in Arson investigation

The experiments performed by Mendel led to the formation of three main principles that dignify genetics i.e.,

  • Law of Independent Assortment
  • Law of Segregation
  • Law of Dominance

1. Law of Independent Assortment

The Law of Independent Assortment states that different pairs of alleles are passed onto the offspring independently of each other. Therefore, the inheritance of genes at one location in a genome does not influence the inheritance of genes at another location.

2. Law of Segregation

For each trait, each parent’s pairing of genes split and one gene passed from each parent to an offspring. Which particular gene in a pair gets passed on is rare.

3. Law of Dominance

This Law states that in a heterozygote, one trait will conceal the presence of another trait for the same characteristic. Rather than both alleles contributing to a phenotype, the dominant allele will be expressed exclusively. The recessive allele will remain “latent,” but will be transmitted to offspring in the same manner in which the dominant allele is transmitted. The recessive trait will only be expressed by offspring that have two copies of this allele; these offspring will breed true when self-crossed.

By definition, the terms dominant and recessive refer to the genotypic interaction of alleles in producing the phenotype of the heterozygote. The key concept is genetic: which of the two alleles present in the heterozygote is expressed, such that the organism is phenotypically identical to one of the two homozygotes.

It is sometimes convenient to talk about the trait corresponding to the dominant allele as the dominant trait and the trait corresponding to the hidden allele as the recessive trait. However, this can easily lead to confusion in understanding the concept as phenotypic.

Read also:  Is DNA evidence 100% reliable in court for conviction?

For example: to say that “green peas” dominate “yellow peas” confuses inherited genotypes and expressed phenotypes. This will subsequently confuse discussion of the molecular basis of the phenotypic difference. Dominance is not inherent. One allele can be dominant to a second allele, recessive to a third allele, and codominant to a fourth. If a genetic trait is recessive, a person needs to inherit two copies of the gene for the trait to be expressed. Thus, both parents have to be carriers of a recessive trait for a child to express that trait.

Applications

  • Using Mendel’s laws, we can determine new combinations in the progeny of hybrids and can predict their frequency. This information is vastly used by plants and animal breeders to produce better breeds. New types of plants with new combinations of useful characters can be produced by hybridization.
  • Forensic identification is a universal method used to establish the truth in the process of forensic investigation. The evidence includes, among other components, the identification but without being mistaken for it or being reduced to just this.
  • Both medico‐legal and criminalities identification are integrative parts of forensic identification, having probative value. The value of an identification method resides in the expert’s ability to compare traces left at the crime scene with traces found on other materials such as reference evidence. Through this method, one can compare traces of blood left at the crime scene with those found on a suspects’ clothes and with samples from the victim. Furthermore, the rifling can be compared with fingerprints left on the weapon and with the rifling of other weapons.
  • Together with the discovery by Mullis in 1983 of the polymerized chain reaction (PCR), Sir Alec Jeffreys introduced DNA in the field of forensic genetics. This technique by studying a set of DNA fragments that proved to have unique characteristics, which were non-recurring and inherent for each individual, the only exception being monozygotic twins. Alec Jeffreys named these reaction products “genetic fingerprints”.

Leave a Reply

Your email address will not be published.