Genetics: Principles of Heredity

The Genetic Principles of Heredity explain how traits are inherited from one generation to the next through genes. Heredity is the biological process of passing traits from parents to offspring. It happens through genes present on chromosomes. These principles explain patterns of inheritance, such as eye color, height, and even genetic disorders.

This Story also Contains

1. What is Genetics?
2. What is Heredity?
3. Variation and its Types
4. Mendel's Laws of Heredity
5. Genetic Disorders
6. Examples of Genetic Disorders
7. MCQs on Genetics

In Biology, Gregor Mendel discovered the basic rules of heredity. These rules explain how traits are inherited. They also help in understanding why offspring look like their parents. These principles form the base of Mendelian genetics. The Principles of Heredity are a part of the Principles of Inheritance and Variation, explaining how traits pass and vary in offspring.

What is Genetics?

Genetics is the study of heredity and how traits are different among living things. It relates to understanding genes and how genes work when transmitted, expressed, and regulated. The basic units of heredity are genes, which in turn control specific characteristics through the synthesis of proteins (process of translation) and other molecules. There are branches of genetics, molecular genetics, population genetics, and evolutionary genetics. It has a huge impact on medicine, agriculture, and biotechnology, making it easier to understand human health, biodiversity, and genetic variety.

What is Heredity?

Heredity is defined as the passing of genetic traits from parents to their offspring through genes. It means that characteristics, such as eye colour, texture of hair, and even some kinds of diseases, can be passed on from generation to generation. Genes are kept in a very small thread-like structure within each cell, called a chromosome. Thousands of genes are carried by the chromosome. The segments of DNA responsible for specific characteristics. In the process of reproduction, genetic material from both parents combines to create a unique genetic makeup in their offspring. This process helps in maintaining continuity in a species while also permitting individual differences and variations.

Variation and its Types

Variation refers to the differences in traits among individuals in a group or population. Such differences can be in physical features, body shape, colour, or even internal traits like how the body works. Such visible or genetic differences are often described using the term polymorphism. Variation is important for evolution and gives rise to adaptation and habitat in species to change in their environment. There are two primary types of variation:

Genotypic Variation

• This comes about as a result of differences in the genes, or alleles, passed from parents to the offspring.

• It gives rise to variations in a population and allows species to thrive in various environments.

• Such traits include physical characteristics and body functions, as well as disease resistance and other protection mechanisms.

Somatic Variation

• These are variations in traits that occur during the lifetime of an organism but are not passed on to the next generation.

• They are caused by diet, environment, lifestyle, or exposure to harmful substances.

• Somatic variation caused by a somatic type of mutation also brings about changes in body cells. Sometimes, it results in causing diseases like cancer.

Mendel's Laws of Heredity

Gregor Mendel, considered the father of modern genetics, established three basic principles of heredity known as Mendel's Laws of Inheritance from his experiments on pea plants, as follows:

• Law of Segregation: Two alleles of a gene segregate during meiosis from each other for gamete formation, such that each gamete carries only one allele of each gene.

• Law of Independent Assortment: Genes for different traits segregate independently of one another in forming gametes, and their inheritance is independent.

• Law of Dominance: Some alleles are dominant and mask the expression of recessive alleles in heterozygous individuals. Dominance relationships determine the phenotypic outcomes of genetic crosses.

Genetic Disorders

Genetic disorders are diseases resulting from abnormalities in an individual's genetic material. Broadly, there are three types of disorders based on the pattern of inheritance of a particular disorder:

• Autosomal Recessive Disorders: Disorders occurring due to the inheritance of two recessive alleles for a gene. Examples include cystic fibrosis, sickle cell anemia, and phenylketonuria.

• Autosomal Dominant Disorders: It results from the inheritance of a single allele copy of a gene. Examples include Huntington's disease, Marfan syndrome, and neurofibromatosis.

• X-linked Recessive Disorders: A result of a mutation in genes found in the X chromosome, much of their effect falls upon males, who have only one X chromosome. Examples are haemophilia, Duchenne muscular dystrophy, and colour blindness.

Examples of Genetic Disorders

Human Genetic disorders manifest themselves in multiple ways and, therefore, impact many of the systems and organs within the body. Some of these disorders are:

• Cystic fibrosis affects the respiratory and gastrointestinal systems.

• Huntington's disease consists of involuntary movements and cognitive decline.

• Chromosomal conditions like Down syndrome result in mental disability along with developmental delays.

Recommended Video on Genetics

MCQs on Genetics

Question: 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

Answer: 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.

Question: Which of the following statements about heredity and variation are true?

1. Heredity is the process of transmission of traits from offspring to parents.

2. Heritable characters are not transmissible.

3. Genetics deals with the inheritance and variation of characters.

4. Variations can only be heritable.

Answer: A) This statement is incorrect. Heredity is the process of transmission of traits from parents to their offspring, not the other way around.

B) This statement is incorrect. Heritable characters are transmissible from parents to offspring.

C) This statement is correct. Genetics is the branch of biology that deals with the inheritance and variation of characteristics.

D) This statement is incorrect. Variations can be heritable or non-heritable.

Hence, Option 3) Genetics deals with the inheritance and variation of characters is the correct answer.

Question: Which of the following statements about DNA is correct?

1. DNA is a double-stranded molecule made up of amino acids.

2. DNA carries the genetic information in the form of genes.

3. DNA is found only in the nucleus of cells.

4. DNA is a protein that provides structural support to cells.

Answer: DNA (deoxyribonucleic acid) is a double-stranded molecule made up of nucleotides, not amino acids. It carries genetic information in the form of genes, which are specific sequences of DNA that provide instructions for the synthesis of proteins and other molecules. DNA is found in the nucleus of cells, but it can also be found in other cell organelles like mitochondria and chloroplasts. DNA is not a protein but a nucleic acid.

Hence, the correct answer is option 2) DNA carries the genetic information in the form of genes.

Also Read:

• MCQ Practice on Genetics

• Gene Interaction

• Molecular Basis of Inheritance