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

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 offspring 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.

Scope and Importance of Genetics

The scope and importance of genetics includes:

• Genetics is concerned with discovering human inheritance patterns.

• Helps understand evolution, and disease in medicine.

• Some basic concepts, which are widely used when studying genetics include genes of heredity, alleles and genotypes, which essentially form the diverse and intricate density of forms of life.

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 store genetic information.

• It enables replication and transmission of traits

• Helps to controls growth, development, and metabolism

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.

Mutation and Variation

• Mutations are changes that happen to DNA.

• They 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.

Mendelian Genetics

The laws of genetics introduced by Mendel are:

Gregor Mendel – Father of Genetics

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

Mendel's Laws of Inheritance

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.

Genetic Crosses

• In a monohybrid cross one gene with two alleles is represented

• In a dihybrid cross, two different alleles of different genes are being tested.

Genetic Crosses

• Punnett square 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 theory affirms that genes are present on the chromosomes

• Behaviour of chromosomes explains Mendelian inheritance.

• Meiosis explains segregation and assortment.

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 frequently in humans because the X chromosome is far larger than the Y chromosome.

• Hemophilia and colour blindness are sex-linked traits.

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 Mapping

• Genetic maps refer to the relative distance between genes that ranges from a few per cent to nearly 100% 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 the 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.

Examples of Genetic Disorders

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.

Genetics NEET MCQs (With Answers & Explanations)

Important questions asked in NEET from this topic are:

• Mendelian Genetics

• Genetic Disorders

Practice Questions for NEET

Q1. Alleles are:

1. different molecular forms of a gene

2. heterozygotes

3. different phenotype

4. true breeding homozygotes

Correct Answer: 1) different molecular form of gene

Explanation:

Alleles are different gene variants or molecular forms that occur at the same location (locus) on a chromosome and are caused by mutations. Different characteristics or variances in an organism can be caused by alleles.

People who have two distinct alleles at a specific gene locus (such as Aa) are known as heterozygotes.
Various phenotypes Although alleles are not distinct phenotypes, phenotypes are the observable qualities or characteristics of an organism that arise from the expression of alleles.
Although this is not the definition of alleles, true-breeding homozygotes are organisms that have two identical alleles for a particular attribute (AA or aa, for example).

Hence, the correct answer is option 1)different molecular forms of a gene.

Q2. What is a phenotype?

1. The genetic makeup of an individual

2. The physical characteristics of an individual

3. The reproductive cells of an individual

4. The expression of a single gene

Correct Answer: 1) different molecular form of gene

Explanation:

A phenotype is the observable physical and biochemical traits of an individual, such as height, hair color, and blood type. It is the result of the interaction between an individual's genetic makeup (genotype) and the environment. The phenotype can also include behavioral characteristics and susceptibility to certain diseases. The genotype refers to the genetic makeup of an individual, including all of the individual's genes and genetic variants. The reproductive cells of an individual are called gametes, and the expression of a single gene is just one part of the complex process that leads to the development of a phenotype.

Hence the correct answer is option 2, The physical characteristics of an individual.

Q3 What is a gene?

1. A unit of heredity that is passed from parent to offspring

2. A type of protein that regulates gene expression

3. A section of DNA that codes for a specific protein

4. A type of RNA that carries genetic information

Correct answer: 3) A section of DNA that codes for a specific protein

Explanation:

A gene is a specific sequence of DNA that encodes the information required to make a functional protein or RNA molecule. This sequence of DNA contains the instructions for the sequence of amino acids that make up the protein, as well as the regulatory sequences that control when and where the gene is expressed. These proteins perform various functions in the body, such as enzymes that catalyze chemical reactions, structural proteins that form the framework of cells, and signalling proteins that regulate cellular communication. Mutations in genes can lead to changes in protein function, which can result in genetic disorders or diseases. In summary, a gene is a fundamental unit of heredity that carries the genetic information necessary to produce a functional protein or RNA molecule.

Hence, the correct answer is option 3) A section of DNA that codes for a specific protein.

Also Read:

• MCQs on Mendelian Genetics

• Mendel’s Laws of Inheritance

• Complementary Genes

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