Introduction to Genetics:
The subject known as genetics involves the study of genes, their mechanisms, regulation, and their pattern of expression. We must know about the genes to study the subject. Specific sequences of the nucleotides are known as the genes. They express a particular phenotype. These entities are also known as the functional units of heredity (transmission of genes from one generation to the next). We all resemble our parents, yet look different. The physical, mental and behavioral characteristics get passed on from the parents to the children, through gametes. In eukaryotes, the genetic material is present in a membrane-bound nucleus within the cells.
Differences between organisms are due to differences in their genetic makeup. These differences occurred due to events such as mutation, recombination, and selection. Mutation leads to a change in the genetic material. The exchange of genetic material between chromosomes is known as recombination. A particular combination of genes chosen in a given environment is known as selection. Mutations may either occur spontaneously or occur due to mutagens. They get permanently incorporated in the genetic code.
Image 1: Introduction to genetics
Basic Terms in Genetics
We must know the basic terms used in genetics.
Cells: The basic functional units in the body, with a full-fledged genetic and biochemical, machinery, are known as cells. They synthesize certain molecules necessary for the body, carry out regulation mechanisms, participate in signaling, and undergo a cascade of events. Right from the synthesis of energy to the functioning of every body part requires the pre-planned efforts of the cells.
Nucleus: Inside the cell, there is a nucleus. It is the main store of genetic machinery.
Chromosomes: The thread-like structures present in the nucleus are known as chromosomes. The chromosomes have different shapes.
Base Pairs: There are four bases in DNA such as Adenine, Guanine, Thymine, and Cytosine. In RNA, uracil is an alternative to the thymine. The sequence of these bases within the strand determines the genetic information.
DNA: Deoxyribonucleic acid or DNA is the hereditary material present in the nucleus of the cell. It is also known as a blueprint for life. It is in the form of a double helix with base pairs attached to the sugar-phosphate backbone.
RNA: The ribonucleic acid is involved in protein synthesis.
In more sophisticated terms, a gene is a sequence that codes for a functional molecule. Gene expression is an important process in all the organisms.
Phenotypic traits: These are the specific characteristics passed on from the parent to offspring. Examples include eye color, skin type, the shape of the nose, etc.
Genotype: Different DNA sequences constitute a genotype. Thus, genotypes combine with the environmental factors and determine the trait or phenotype.
Homozygous organism: An organism having a pair of identical alleles is said to be homozygous.
Heterozygous organism: An organism having two different alleles is said to be heterozygous.
Heterozygous organism: An organism having two different alleles is said to be heterozygous.
The Discovery of Genetics
Mendelian Genetics (1856-1866):
Gregor Mendel was an Austrian monk in the 19th century. He was the pioneer in genetics. His experiments on pea plant led to the discovery of the basic mechanisms of the heredity. Mendel established the basic principles of heredity. This study is known as Mendelian genetics. Later on, various researchers came up with interesting concepts in the field of genetics.
Gregor Mendel is known as the father of modern genetics. He worked on pea plants.
Image 2: Mendel and his study on the pea plants
The DNA era (1944-1972):
It started with Avery's experiment which demonstrated isolation of DNA as a genetic material (also known as transforming principle). Transposons were discovered later on by other scientists.
Discovery of Genomic science (1972- 2016):
The genomics era started with Walter Fiers's discovery of the genetic sequence for a bacteriophage. Likewise, Sanger, Maxam, and Gilbert sequenced the DNA for the first time. The computer stores important information in databases. There are many genetic databases available on the internet. One of the examples of genetic databases includes the National Center for Biotechnology Information (NCBI). A genetic database consists of a store of researched documents, computational biology data, genomic data software and other useful information. Gene maps show the location of genes on chromosomes. The position of a gene on the chromosome is known as gene locus. The unit of genetic distance is known as the map unit. Genetic maps are used to study the organization of genes on the chromosomes. They are used to obtain complete genome sequences.
Many discoveries led to advances in genomic science such as:
· The DNA sequencing
· Nucleic acid labeling
· Mapping the structure of DNA
· Gene Cloning
· Transposon-mediated mutation and chromosome breakage studies
· DNA fingerprinting
· CFTR protein sequencing
· Identification of BRCA gene
· Cloning of Dolly sheep
· Genome sequencing of Drosophila
· Development of Human Genome Project
· Genetic Databases and Maps
Branches of Genetics
Four main branches of genetics are:
Human genetics: It is the study of inheritance in humans.
Plant genetics: It is the study of genes and inheritance in plants.
Animal genetics: It involves the study of genes in animals. Genetic engineering is used to breed animals with a specific trait. Animal geneticists develop genetically modified animals.
Microbial genetics: Various genetic mechanisms also occur in microbes such as bacteria, fungi, and viruses. Microbial genetics is the study of genetic mechanisms in microbes.
Image 3: Branches of genetics
Based on the above categories, genetics can be further studied as follows:
Classical genetics: It is the oldest branch of genetics that depends only on the physical characteristics of an organism. It involves the study of Mendelian Inheritance.
Molecular genetics: It involves the study of the structure and function of the genes at molecular levels.
Cytogenetics: It mainly deals with chromosomes and cellular behavior.
Biochemical genetics: It involves the study of biochemical processes, metabolic disorders and the role of genetic machinery.
Medical genetics: It helps in diagnosing genetic disorders.
Epigenetics: It is the study of heritable changes in gene function under the influence of certain environmental factors. It covers important aspects such as DNA methylation and histone modification.
Developmental genetics: It is the study of genes and their way of controlling the growth and development of an organism.
Behavioral genetics: It involves genetic science to understand the behavior of an individual or an organism.
Population genetics: It is a study based on evolutionary biology and Mendelian inheritance. Population genetics involves the study of particular traits, changes in alleles and genotypes in a population.
Ecological genetics: It involves a combination of genetics and ecological sciences. In layman terms, ecological genetics is the study of natural populations.
Genetic engineering: It is a direct way of manipulating the gene of an organism to get the desired trait.
Genetics of intelligence: It uses genetics to determine the I.Q. of an individual.
Genomics: It is a study of structure, function, evolution, and mapping of the genomes.
Importance of Genetics in Medicine
A large number of diseases have a genetic background. That is why genetics plays a crucial role in medical science. Genetics may be used to avoid disorders related to genes and chromosomes. With the latest genetic techniques such as prenatal diagnosis, it is easy to detect the chances of abnormalities in the fetus.
Role of Medical Genetics
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Table: Role of Genetics in medicine and healthcare
Genetic Engineering
Genetic engineering involves modification or cloning a specific gene preferably involving a vector. Many drugs and hormones such as insulin, somatostatin, blood clotting factors and growth hormones are synthesized using recombinant DNA technology. Synthetic vaccines such as anti-rabies, anti-malaria, anti-hepatitis vaccines are produced using genetic engineering.
Genetic alterations to the plants may improve the quality of the crop. Such crops may be able to satisfy human needs. For example, disease resistance to plants can be achieved using gene alteration. Other desirable traits include stress resistance, drought resistance and tolerance to extreme conditions, salinity and temperatures.
References:
[1] Genetics, Daniel Hartl, 2011, Preview
[2] IGenetics, a molecular approach, Peter Russel, second edition
[2] IGenetics, a molecular approach, Peter Russel, second edition
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