Genetics: Definition, Examples, Meaning, Facts, Topics, Timeline

Genetics is the study of how traits and characteristics are passed from one generation to the other. This field helps explain how genes and DNA determine things such as eye colour, height, and even health conditions. This topic is from the Class 12 chapter on the Molecular Basis of Inheritance in Biology. Questions are often asked in competitive exams such as NEET and AIIMS BSc Nursing.

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This Story also Contains

1. What is Genetics?
2. Basic Concepts in Genetics
3. Mendelian Genetics
4. Chromosomal Basis of Inheritance
5. Genetic Disorders

What is Genetics?

Genetics involves the investigation of genes and their characteristics in living organisms in the field of science. It studies how characteristics are passed to children and is broader to include all the processes that dictate these occurrences. Traditionally, a basis of modern genetics has been set by Gregor Mendel, whose works on pea plants in the nineteenth century provided knowledge about heredity.

Genetics is concerned with discovering human inheritance patterns and participates in the process of improving our knowledge of the molecular and cellular mechanisms of life phenomena, evolution, and disease in medicine. Some basic concepts, which are widely used when studying genetics include genes of heredity, alleles that are the differentiation of genes and genotypes, which essentially form the diverse and intricate density of forms of life.

Also Read:

• MCQ Practice on Genetics
• Principles of Inheritance and Variation
• Mendelian Genetics
• Molecular Basis of Inheritance

Basic Concepts in Genetics

The basic concept of genetics in biology includes the following:

Genes, Alleles, and Chromosomes

A gene refers to a segment of DNA sequence that is responsible for the inheritance of characters and it is found on chromosomes which are slender structures observed in the atomic nucleus of the cell. They may refer to the different forms of a single gene known as alleles which can cause differences in the levels of a character in different individuals.

DNA Structure and Function

DNA is composed of double-stranded molecules that provide instruction on how organisms develop, how they function, how they grow as well as replicate. It has a twisted scale like a ladder and therefore it is suitable for replication and transmission of genetic information to take place.

Genetic Code and Protein Synthesis

Genetic code is a code according to which the sequences of genomes, that is DNA sequences, are translated into amino acid sequences while the formation of proteins. This translates into transcription, which is the formation of the mRNA from the DNA, and translation, the process by which proteins are assembled from the mRNA within cellular machinery.

Mutations are any changes that happen to DNA, which can occur randomly by chance or as a result of other influences in the environment. They may cause alterations in protein conformation or activity that modify an inherited characteristic and may be implicated in disease or serve as the basis for adaptation in probes or populations. Mutations are an important concept in genetics and one of the highly essential factors for understanding genetic and phenotypic diversity and disease processes.

Mendelian Genetics

The laws of genetics introduced by Mendel are:

Mendel's Laws of Inheritance

Prelude to Gregor Mendel’s experiments on pea plants put into place important principles on the inheritance of certain characteristics:

Law of Segregation: Every person has two alleles for a specific trait, and after the formation of the gamete these alleles separate which makes certain that at least one allele is transferred from each parent to the next generation.

Law of Independent Assortment: For different traits, genes pair up randomly during gamete formation which creates the variation needed in a population.

Monohybrid and Dihybrid Crosses: In a monohybrid cross one gene with two alleles is represented whereas in a dihybrid cross, two different alleles of different genes are being tested.

Punnett Squares: There are different methods of using punnett squares and one of the methods is using punnett squares, which helps to predict the genotypes and phenotypes of offspring as a result of inherited alleles from parents. They show there are diploid organisms, and demonstrate the dominant and recessive alleles and the probabilities of inheritance for monohybrid and dihybrid crosses through simulation.

Chromosomal Basis of Inheritance

The study on genetics indicated that the inheritance of all traits can be fundamentally guided by the behaviour of chromosomes during cell division.

Chromosome Theory of Inheritance

The chromosome theory of inheritance affirms that genes are present on the chromosomes and that characteristic processes of chromosomes during the process of meiosis can explain the traits of Mendelian genetics. This theory combines the rules given by Mendel and the cytological studies of chromosomes.

Sex-Linked Inheritance

A sex-linked trait therefore is any characteristic that is determined by genes that are found in the sex chromosomes, that is X and Y. Dominant conditions affect men more frequently in humans because the X chromosome is far larger than the Y chromosome. Hemophilia and colour blindness are sex-linked traits. About 1% of male children are colour blind while only a few female children can be colour-blind.

Linkage and Crossing Over

Alleles of different genes that are tightly connected and situated on the same chromosome are called linked genes, they are co-inherited. Pairing up, and crossing over results in genetic recombination and can un-link linked genes, for the two homologous chromosomes hand over their genetic material to each other during meiosis.

Genetic Maps and Recombination Frequencies

Genetic maps refer to the relative distance between genes that ranges from a few per cent to nearly 100% of the organisms’ total genome based on the recombination frequency evident in offspring. Thus, high recombination frequency signifies that genes on a chromosome are located far apart, which is useful in the construction of maps of the chromosomes.

Genetic Disorders

Genetic disorders refer to those diseases that are contracted as a result of an individual's genes or chromosomes not functioning adequately or not being present in the right amount. These disorders can be inherited from the father or mother or both parents or can be caused by a new mutation that was not present in either parent. It is a group of diseases that manifest on the gene level and can influence human health and development with signs of varying severity.

Examples of genetic disorders include:

Cystic Fibrosis

Particularly, the lungs and digestion system are suffering from the symptoms of hard breathing and digestive issues as a result of a genetic disorder of salt and water transportation inside cells.

Down Syndrome

An extra chromosome 21 causes individuals to suffer from intellectual problems, facial appearance, and other body complications like cardiovascular diseases.

Hemophilia

A genetic disorder that entails the failure of blood to coagulate as an outcome of genetic factors that regulate clotting factors.

Sickle Cell Disease

It is a heredity disease that is concerned with red blood cells where they transform making their form hard and sticky to cause some level of pain in the body it also interferes with the transportation of oxygen in your body.

Huntington's Disease

A disease that is a hereditary disorder which causes a condition that involves irregular twisting movements, mood and thinking disorders, as well as dementia.

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