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Genetics

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Genetics - is one of the most important branch of biology. This part of science is concerned with genes, heredity and variation in living organisms. The word genetics stems from the ancient Greek meaning "genitive"/"generative", which derives from "origin".

 

Depending on the object of the research, there are some types of genetics (genetics of plants, animals, microorganisms, humans), so depending on the way of the research, genetics can be molecular, environmental.

Ideas and methods of genetics play the important role in medicine, agriculture, microbiological industry, genetic engineering.

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History

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The first word "genetics" was used by the Hungarian nobleman Imre Festetics, who described several rules of genetic inheritance in his work "The Genetic Law of Nature".

The origins of genetics lie in the development of theories of evolution. It was in 1858 that the origin of species and how species variability was developed after the research work of Charles Darwin and Wallace. They described how new species arose via evolution and how natural selection occurred to evolve new forms. They did not know the role genes had to play in this phenomenon.

 
Mendel's theory

Mendelian and classical theories of genetics

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The beginning of modern genetics originates in the works of the Augustinian monk Gregor Mendel in the middle of the 19th century. Consequently, Gregor Mendel is known as the Father of Genetics.

His work is in fact the basis of understanding the principles of genetics even today. In his work "Experiments on Plant Hybridization" Mendel traced the patterns of inheritance of some traits in pea plants and mathematically described them. Mendel's work suggested that heredity was partial, not acquired, and that patterns of inheritance for many traits could be explained by using simple rules and relationships.

However, Thomas Morgan is one more important person of classical genetics. He was an American evolutionary biologist, geneticist. Studying the fly Drosophila, which has only four pairs of chromosomes, a high reproduction rate and a short life span, the scientist formulated the chromosomal theory of heredity.

Molecular genetics

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However, genes were known to exist on chromosomes, chromosomes are composed of both protein and DNA, and scientists did not know which of the two is responsible for inheritance. Frederick Griffith, British bacteriologist, discovered the phenomenon of transformation, which consisted in the fact, that dead bacteria could transfer genetic material to "transform" other still-living bacteria. So, some years later the Avery–MacLeod–McCarty experiment dentified DNA as the molecule responsible for transformation.

Features of inheritance

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Genetic inheritance is a basic principle of genetics and explains how characteristics are passed from one generation to the next.

Mendel was the first person to correctly understand the process of how characteristics are inherited by offspring from parents. Mendel performed a series of experiments of 7 different characteristics, each with 2 different traits. After crossing the first generation of offspring with each other, Mendel found that approximately 75% of the second generation inherited the same trait as their parents and the remaining 25% expressed the second trait of the original parents, the trait that appeared to be lost in the first generation of offspring.

Following three generations of cross-breeding Mendel produced three significant conclusions regarding genetic inheritance. His first conclusion was that each trait is passed on unchanged to offspring via ‘units of inheritance’. These units are now known as ‘alleles’.

Mendel’s second conclusion, offspring inherit one allele from each parent for each characteristic. His third and final conclusion was that some alleles may not be expressed in an individual but can still be passed on to the next generation.

Gene expression

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Gene expression is the process when DNA directs the synthesis of functional products such as proteins.

 
Regulation of gene expression by steroid hormone receptor

The amounts and types of mRNA molecules in a cell reflect the function of that cell. In fact, thousands of transcripts are produced every second in every cell. RNA transcription makes an efficient control point because many proteins can be made from a single mRNA molecule. Transcript processing provides an additional level of regulation for eukaryotes, and the presence of a nucleus makes this possible. In prokaryotes, translation of a transcript begins before the transcript is complete, due to the proximity of ribosomes to the new mRNA molecules. In eukaryotes, however, transcripts are modified in the nucleus before they are exported to the cytoplasm for translation.

Model organisms

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Emerging model organisms

Model organisms are non-human species that are used in the laboratory to help scientists understand biological processes. These organisms share many genes with humans, are easily maintained in the lab, and have short generation times that make it easy to study the effects of genetic manipulations.

There are some of the most popular types of model organisms:

  • Drosophila melanogaster or the fruit fly. It has been used in scientific research for over a century. The fruit fly makes a great model organism because they are easy and not very expensive to grow in the lab, have a short life cycle of 8 to 14 days and produce a large number of offspring that are laid externally.
  • The mouse (Mus musculus). Mice have many advantages as a mammalian model organism for scientists as they have a relatively short generation time for mammals - the time between being born and giving birth - of about 10 weeks. Adult mice reproduce as often as every three weeks so scientists can simultaneously observe several generations of mice at a time.
  • Zebrafish (Danio Rerio). They share about 70% of their genes with humans and 85% of human genes associated with a disease have a homolog in zebrafish (Howe et al., 2013). Zebrafish are small, easily maintained as they are housed in large groups, easily bred, and produce 50-300 eggs at a time.

Genetic change

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Mutations

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A gene mutation is a permanent alteration in the DNA sequence that makes up a gene, such that the sequence differs from what is found in most people. Mutations are the basis of evolution as well as genetic disorders. Genetic mutations can change proteins and cells function.If mutations occur in non-germline cells, then these changes can be categorized as somatic mutations.

 
Drift of genes

A single mutation can have a large effect, but in many cases, evolutionary change is based on the accumulation of many mutations with small effects. Mutational effects can be beneficial, harmful, or neutral, depending on their context or location. Most non-neutral mutations are deleterious. In general, the more base pairs that are affected by a mutation, the larger the effect of the mutation, and the larger the mutation's probability of being deleterious.

Types of mutations

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  • Duplication or triplication of segments of DNA.
  • Deletions of vital segments.
  • Point mutations affect a single amino acid or short sequence.
  • Translocation. This is when a chromosome segment rearranges from one location to another. It can happen either within the same chromosome or move to another chromosome.

Research methods

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DNA can be manipulated in the laboratory.

Mutations and human health

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Unfortunately, there are mutations, which provides lots of diseases. For example, all types of mutations can cause cancer.

Sections of genetics

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Methods of genetics

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  • Hybridological - the main method of genetics. The study of the hereditary properties of an organism by crossing it with a related form and subsequent analysis of the characteristics of the offspring.
  • Cytogenetic - the study of the structure and number of chromosomes.
  • Biochemical - the study of changes in the biochemical parameters of the body resulting from a change in the genotype.
  • Ontogenetic - the study of the manifestation of a gene in the process of ontogenesis.
  • Population - the study of the genetic composition of populations. This method helps to find out the distribution of individual genes in a population and calculate the frequency of alleles and genotypes.
  • Genealogical - the study and compilation of pedigrees. Helps to set the type and nature of inheritance of traits.
  • Twin - study of twins with the same genotypes. Allows you to find out the influence of the environment on the formation of various signs.
  • Genetic engineering - is the use of natural or artificially created genes.
  • Mathematical - statistical processing of the received data.

CRISPR and other methods of editing human genomes

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CRISPR is a family of DNA sequences found in the genomes of prokaryotic organisms such as bacteria and archaea

In 2012, researchers demonstrated that RNAs could be constructed to guide a Cas nuclease to any DNA sequence. Further testing revealed that the system works quite well in all types of cells, including human cells.

 
CRISPR system

But any such edits in humans would not only affect an individual but also his or her progeny. They could also theoretically be used to enhance desirable traits instead of curing disease. Scientists have therefore called for a moratorium on human germline editing until the serious ethical and societal implications are more fully understood.

Genetics and society

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Moreover, genetics is the great opportunity in the questions about life extension and the creation of pure genotypes. However, there are some scandals connected to the modern genetics methods. For example, in 2015 the clinical use of methods for editing the human genome (CRISPR and zinc finger) was prohibited in the whole world.

See also

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Further reading

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  • Matt Ridley (May 2006). "The Autobiography Of A Species In 23 Chapters"
  • Koonin EV, Makarova KS (December 2009). "CRISPR-Cas: an adaptive immunity system in prokaryotes".
  • Michael Cummings (June 1962). "Human Heredity: Principles and Issues"
  • Richard Dawkins (1982). "The Extended Phenotype: The Long Reach of the Gene"
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  • genetics https://www.nature.com/subjects/genetics
  • genetic change https://www.news-medical.net/life-sciences/Genetic-Change.aspx
  • heredity https://www.britannica.com/science/heredity-genetics
  • five popular model organisms https://blog.addgene.org/plasmids-101-five-popular-model-organisms
  • gene mutation https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5126403/
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