The Science behind Genetics and Mendelian genetics

Introduction to Genetics and Mendelian genetics

Genetics is the scientific study that tackles heredity and how genes generate variations in living organisms. It accounts for an essential pillar of biology whilst converging with many other fields, including medicine and agriculture. Early stages of civilisation point toward acknowledging the principles of heredity, which we usually apply in improving cattle and crops. Ancient carvings reveal the utilisation of cross-pollination techniques on palm trees.  The 1800s saw the inception of genetics as an organised scientific discipline with Mendelian genetics laws.

Genetics is said to have sprouted after genes (DNA-based functional and physical units that makeup heredity) were identified. Genetics deals with genes at every level, including how they behave in cells and their transfer to offspring. 

Modern genetics tackles deoxyribonucleic acid (DNA).

Gregor Mendel is said to have triggered the scientific field of genetics in the mid-1800s. He acknowledged the presence of units that gave rise to the inheritance of certain traits. This knowledge founded how heredity is understood today.

The term genetics, however, was coined by William Bateson, an English biologist, in 1905. He contributed to the discovery of the work done by Mendel.

The History of Genetics

Despite Mendelian genetics being the foundation of the field, studies revealed that human beings showed interest in heredity even before civilisation came to being. These interests may have sprouted from resemblances within the family, including traits such as voice, height, body structure and the like. 

Early speculations on the topic are said to have first appeared during the early ages of the Greeks.

Hippocrates advocated the idea of inheriting traits from parents, and to prove this; he formulated his hypothesis called pangenesis. Aristotle was a proponent of the idea that blood played a pivotal role in heredity. People still use terms such as "blood ties" and "bloodlines" to address certain traits. 

What is Mendelian Genetics? And Define Mendelian genetics?

Preformation & natural selection

The 17th & 18th centuries saw the inception of novel ideas about heredity. One of those ideas was the concept of preformation. Scientists hypothesised the envisioning of miniature models of humans in sperm heads. Lamarck argued that acquired traits pointed towards evolution. He opined that we could only find rigidity in species in rigid environments. Additionally, he argued that certain organs develop according to their environmental needs. 

Wallace, a British naturalist, formulated the theory that stated the idea of evolution through natural selection. Charles Darwin contributed to the evidence of natural selection and the idea that animals and humans share one common ancestry.

Numerous scientists who advocated the concept of pangenesis disregarded Darwin's ideas as they did not align with Mendel's work.

Principles of mendelian genetics

 Long before Mendel worked on heredity, the concept was explained solely through speculation and logic and lacked experimentation. Mendelian Genetics included experiments on cross-pollination betwixt different garden pea variants. He crossed his yellow seeded peas with those that had green seeds. This resulted in yellow progeny seeds (F1). When crossed within themselves or self-pollinated, these seeds generated progeny that was 1/4 green and 3/4 yellow, depicting a 3:1 ratio. He concluded that because the F2 bunch comprised of some green variants, the F1 generation must have contained what determined their greenness despite its lack of expression in greenness and dominating yellow-green.

He found various other instances in the ratio of 3:1. Later, he concluded the presence of distinct units (genes) and that these units came in pairs which later separated whilst gamete formation. 

He concluded that the original pea plant group was YY (yellow) and yy (green). These plants gave rise to Y and y gametes generating generation F1 (Yy) of yellow peas owing to yellow being dominant. Generation F2 saw random mating resulting in Yy (1/4), YY (1/2) and yy (1/4), proving the ratio of 3:1. 

Stage II

Mendel experimented on another set of pure line peas with varying features, including seed colour (green vs yellow) as well as the shape of seed (wrinkled vs round). When seeds of the yellow round variant mixed with those of the green wrinkled variant, an F1 progeny generation occurred with round yellow peas. This revealed that round and yellow characteristics were dominant. 

The F2 progeny, however, when self-pollinated among F1 plants, generated a 9:3:3:1 ratio where 9/16 showed yellow round characteristics, 3/16 showed yellow wrinkled characteristics, 3/16 revealed green round characteristics and 1/16 revealed green wrinkled characteristics. One can note that this ratio is from two combined ratios of 3:1. This and many other experiments proved that gene pairs separate during the formation of a gamete.

Although the concept of genes in these experiments was hypothetical, the 1900s saw major milestones in the concept and its understanding.

Linked genes

Geneticist and American zoologist T.M. Morgan defended that genes were related to chromosomes. This demonstration involved parallel inheritance regarding the genes of a certain fruit fly on chromosomes that determined sex. He and his student, A. H. Sturtevant, revealed the link between certain genes with one chromosome. In addition, he also found a way to measure their proximity by the rate at which new combinations of chromosomes sprouted.

The early stages of molecular genetics 

British physician Garrod, in 1908, brought to light the idea of linked genes undergoing molecular action at the cell level. This came out when he argued that hereditary diseases such as alkaptonuria stemmed from innate metabolism errors. Molecular genetics came to being in 1941 owing to American geneticist Beadle and biochemist Tatum. The idea is that various studies fortified the genes code of certain proteins.

American bacteriologist Avery, Canadian American geneticist MacLeod and American biologist McCarty argued that genes in bacteria are from DNA. Later, he applied this to all living organisms.

DNA & the genetic code

It was a great achievement when Watson, an American biophysicist and geneticist, along with Crick and Wilkins, British biophysicists, in the year 1953, formulated a DNA model with a helical structure. This particular structure was brought to light by British scientist Franklin who used x-ray to arrive at that conclusion. Seymour Benzer, a molecular biologist in 1955, revealed that the gene exhibited a linear structure.

Crick and Benner, in 1961, argued that we should read genetic code as nucleotide triplets known as codons. Yanofsky, an American geneticist, shed light on the idea that mutant site positions in genes aligned with positions of modified amino acids in the sequence of amino acids with the corresponding protein. Nirenberg and Khorana, in the year 1966, deduced the genetic code of all 64 codons and certain amino acids they code for. Further studies revealed that all organisms exhibited DNA with a double helix structure, the same mode of replication and genetic code.

Technology and recombinant DNA 

Technology has played a pivotal role in the understanding of genetics. American microbiologists Nathans and Smith, in the year 1970, brought to light that restriction enzymes cut DNA according to certain nucleotide target arrangements. This discovery triggered the invention of an artificial molecule of recombinant DNA through the isolation of different molecules of DNA, cutting and joining them in a test tube.

American biochemists Boyer and Cohen further devised methods that allowed the production of recombinant plasmids, which reproduced naturally after insertion into bacterial cells. Various technologies allowed the examination of the genetic structure through nucleotide sequencing.

Canadian biochemist Smith, during the 1970s, created a revolutionary method that allowed for the redesigning of genes by instigating especially modified mutations at distinct genetic sites. This method came to be called site-directed mutagenesis.

Subfields of genetics

Classical genetics

This field laid the footing for all subfields of genetics. Its chief focus lies in genetically transmitted genetic traits (dominant, recessive, intermediate or polygenic) in animals and plants. We may either attribute genetic traits to sex or autosomal. Classical genetics commenced when Mendel performed his experiment with garden peas. It continues to develop as studies in inheritance within animals and plants are performed. In current times, classical genetics allows for the discovery of genes.

Cytogenetics

Cytogenetics refers to the study that tackles chromosomes and the DNA structure. It fuses the efforts of both cytologists and geneticists. Whilst the formerly discovered chromosomes and how chromosomes are duplicated and separated in the course of cell division, the latter grasped how genes behave at the cell level. 

Plant cytogenetics stemmed from the argument that plant chromosomes are much larger than animal chromosomes. 

On the other hand, animal cytogenetics gained importance after the technique squashed cells flat on the glass and observed them under a microscope.

Microbial genetics

Microbial genetics is a subfield of genetics that tackles microorganisms. Although initially neglected by geneticists owing to their small size, lack of variable traits and sexual reproduction, the discovery of their characteristics led to the upsurge in their interest in geneticists. Their size and rapid reproduction became a topic of interest amongst geneticists. Bacteria became one of the most genetically analysed microorganisms. Bacterial genetics revolutionised cloning technology.

The field that studies the genetic makeup of viruses is called viral genetics.

Molecular genetics

This subfield of genetics tackles DNA at the molecular level, including how its cells replicate and how they impact the determination of the genetic makeup of organisms. Molecular genetics immensely depend on recombinant DNA technology, which alters organisms by affixing foreign DNA, giving rise to transgenic organisms. Gene therapy is on transgenesis. It strives to treat genetic disorders by affixing normal genes sourced through external sources.

Genomics

Genomics plays a significant role in genetic research in current times. It stemmed from routinely employing technology that sequenced the DNA of entire genomes. Genomics allows the analysis of genes at a larger level. 

Population genetics

We use the subfield called population genetics to tackle the genes within a population of microbes, plants and animals. It sheds light on evolutionary relations, past migrations, the degree of mixing amongst a multitude of species and how they adapt to environmental changes. It employs mathematics that calculates the frequency of alleles and genetic types within populations. Population genetics has allowed practitioners to analyse human beings' originator and migratory routes.

Behaviour genetics

Behaviour genetics tackles and analyses how heredity causes certain behaviour patterns. We analyse various genetically related animal behaviour, leading to them being treated similarly to biological properties. Human behaviour, however, becomes an arduous task to analyse genetically owing to environmental influences (for instance, culture). Genomics aids in the analysis of genetic factors that shape the behaviour of human beings.

Human genetics

This subfield of genetics tackles the hereditary activities related to the genetics of human beings. Geneticists who specialise in this field pan their focus on comprehending and treating genetically stemmed disorders. Other activities include laboratory-related research that studies how human genes function. 

Procedures involving genetics

Cytogenetic techniques

This method involves microscopic observation of genetic elements of cells, including genes, gene products and chromosomes. Additionally, cytogenetic methods include microscopic studies of cells by placing them in wax and slicing thin segments. Cytogenetics diagnoses chromosomal anomalies that lead to disorders, including Down syndrome.

 Physiological techniques

These methods, although chiefly inclined towards analysis of functions of organisms, also aid in gene-related examinations. A majority of genetic variations in microorganisms require substantial cell function. For instance, we can differentiate strains of E Coli bacterium by putting them on a mixture free of thiamin. It is observable that the grow strains contain the gene required for the enzyme while those that do not grow lack such genes.

 Immunological methods

These methods aid in the determination of blood groups while blood transfusions, Rhesus incompatibility during childbirth and organ transplants. Certain antigens carry genetic correlations with human diseases, while antibodies exhibit genetic bases. Immunological techniques aid in identifying certain clones of recombinant DNA that helps synthesise certain proteins. 

 Mathematical techniques

Mathematical techniques are widely used in genetics owing to the quantitative nature of the data involved. Geneticists employ statistics to calculate deviations from estimated results during experimental genetic analysis. So, we utilise probiotic laws in crossbreeding and aid in predicting how frequently certain genetic constitutions appear in offspring. Bioinformatics utilises computer programs that scan DNA, detecting genes and determining their potential function according to similar genes.

 Biochemical techniques

We perform these techniques on extracts of cells. And administered on primary genetic compounds such as RNA, protein and DNA. They aid in the determination of genetic activity in cells. We subdivide ground-up cells and chemicals for further genetic examination in a certain approach.

 Molecular methods

These techniques overlap biochemical techniques and involve the immediate examination of DNA. A donor such as a human being could donate DNA which could then be removed from the chromosome and placed in a vector, thereby producing recombinant DNA. 

 Experimental breeding

This procedure involves crossing a variety of organisms in a manner that produces distinct allele combinations. For instance, the F1 generation produced through parental crossing lines undergoes mating randomly, producing offspring characterised by pure breeding genotypes (DD, cc, bb, AA). 

Application of genetics

1. Genetics in industries

A multitude of industries makes use of genetics. We hire geneticists, for instance, to facilitate yeast strains in brewing industries to produce alcohol. So, pharmaceutical industries employ science to develop strains of bacteria, mould and other microorganisms that yield antibiotics. For instance, fungi produce penicillin while bacteria yield ampicillin.

2. Animal husbandry and Agriculture

Plants and animals are improved genetically by employing myriads of genetic techniques. In addition, we employ recombinant DNA methods for transgenic alteration and breeding analysis. As a result, artificial insemination is a common technique used by animal breeders who propagate prized animal genes.

3. Medicine 

We diagnose inherited human diseases with the aid of genetic techniques. Family history related to certain conditions such as asthma or other disorders may help indicate the likelihood of developing those conditions. Cells extracted from the embryo may indicate genetic anomalies such as a deficiency of enzymes, thereby allowing early treatment.

Conclusion

Genetics is a highly complex and advanced branch of science; it began as a study in the classical period and established itself with Mendelian Genetics. Mendelian genetics was not advanced, it was the basics but it is where every advancements in the field that we see today began.