Inheritance Definition: Meaning, Synonyms, Issues, & Facts

Inheritance refers to the passing down of genetic traits from parents to their offspring. The offspring get the genetic information from their parents. Therefore, inheritance is the reason why the parents and their children have similar characteristics.

These traits are passed on by parents, including eye colour, hair colour, and blood group. Diseases can also be passed on to the offspring from their parents. Humans have 22 pairs of autosomes and one pair of allosomes or sex chromosomes, for a total of 23 chromosomes. Inheritance is a topic of the chapter Principles of Inheritance and Variation in Biology.

This Story also Contains

1. What is Inheritance?
2. Basic Concepts of Inheritance
3. Mendelian Inheritance
4. Non-Mendelian Inheritance
5. Sex-Linked Inheritance
6. MCQs on Inheritance
7. Recommended Video on Inheritance Definition

What is Inheritance?

Biological inheritance is a process in which genetic information is passed from parents to offspring. Put differently, the transfer of traits from one generation to the following takes place through genes, which are described to be the basic units of heredity. Understanding inheritance is therefore important if one needs to understand how traits and characteristics are passed on to cause variations within a species.

Inheritance is the basis for the major field of biology known as genetics, which is tailored to variation and the transmission of traits.

The study of inheritance allows prediction regarding the patterns of traits and accounts for particular disorders genetically transmitted in families due to chromosomal abnormalities. It also finds application in techniques of genetic engineering for health and agriculture. The basic principles of inheritance form the basis of advances in medicine, biotechnology, and evolution.

Basic Concepts of Inheritance

Inheritance is linked to concepts such as genes, chromosomes, alleles, and the way they express themselves in genotype and phenotype. The concept of inheritance is described below:

Genes and Chromosomes

Genes are short stretches of DNA that encode proteins, which determine the expression of certain traits. They are located on chromosomes, which are long helices of DNA wrapped around proteins called histones. There are 23 pairs of chromosomes in humans, with each one containing thousands of genes. Chromosomes ensure the proper distribution of genetic material during cell division and, hence, may be considered responsible for heredity.

Alleles

Alleles are the variants of genes that produce variation in a given trait. Dominant alleles mask the presence of other alleles, although sometimes allele expression is only seen if the organism has two copies of the allele. For example, the allele for purple flowers, P, is dominant over that for the white version, p, at the same locus in pea plants. An individual who contains two copies of the same allele for a given trait is homozygous (PP or pp). An individual who contains different alleles at a particular locus is heterozygous; in this case, that would be Pp.

Genotype and Phenotype

Genotype refers to the genetic constitution of an organism, that is, all its genes and alleles. The phenotype is the expression of the genotype resulting from the interaction of the genotype with environmental factors. In pea plants, the PP or Pp genotype will produce the phenotype known as purple flowers and the pp genotype will produce white flowers.

Mendelian Inheritance

Mendelian inheritance is the transmission of traits from parents to offspring following Mendelian genetics. The Mendelian Inheritance is given below:

Laws of Mendelian Inheritance

Gregor Mendel, the Father of Genetics, formulated laws of inheritance based on his experiments with pea plants. The Law of Segregation says that as gametes are made, the two alleles for a given trait separate, and thus each contains just one allele. The Law of independent assortment states that during the formation of gametes, alleles segregate separately, resulting in each possible genetic combination.

Monohybrid Cross

A monohybrid cross is a cross for a single trait. All possible genotypes and phenotypes that will result in offspring from parents of known genotypes can be predicted using a Punnett square. Such as crossing homozygous dominant (PP) with homozygous recessive (pp) will yield all heterozygous offspring (Pp) with the dominant phenotype.

Dihybrid Cross

A dihybrid cross examines two traits simultaneously. A Punnett square for a dihybrid cross is larger because it includes all possible combinations of alleles for both traits. For instance, crossing plants heterozygous for the seed shape (Rr) and seed colour (Yy) gives offspring in the ratio 9:3:3:1, a result that describes Mendel's Law of Independent Assortment.

Non-Mendelian Inheritance

Non-Mendelian inheritance does not follow the pattern of Mendelian genetics of complete dominance and segregation. The Non-Mendelian Inheritance is given below:

Incomplete Dominance

Incomplete dominance is a phenomenon where the expression of the heterozygous phenotype is an intermediate mixture of two homozygous phenotypes. For instance, in snapdragons, crossing the flower colour with red (RR) with white (rr) results in the pink colour in the offspring, Rr.

Codominance

In codominance, both alleles are expressed fully in the heterozygote. The classical example is the ABO blood group system in human beings. For example, IA and IB alleles produce A and B antigens on the red blood cells and result in AB blood type.

Multiple Alleles

Multiple alleles refer to the presence of more than two alleles of genes in a population. Inheritance of blood group systems ABO typifies this, whereby three alleles (IA, IB, i) determine four blood types: A, B, AB, O.

Polygenic Inheritance

Polygenic inheritance is a condition where more than one gene controls a particular trait, causing continuous variations. Skin colour in human beings is a polygenic character controlled by several genes which contribute to the gradation of skin colours found amongst the population.

Sex-Linked Inheritance

In Sex-linked inheritance, there is transmission of traits that are present on the sex chromosome in males and females. The Sex-linked Inheritance is described below:

Sex Chromosomes

Sex is determined by the sex chromosomes, X and Y. For sex determination to take place, what is required is that females must have two X's, while males should have XY chromosomes. These contain genes for sex-linked characteristics.

X-Linked Inheritance

X-linked inheritance refers to genes on the X chromosome. Specific disorders such as colour blindness and haemophilia are more common in males than females. Since there is only one X chromosome, it carries a single recessive allele of some genes on the X chromosome that express the trait.

Y-Linked Inheritance

Y-linked inheritance refers to genes on the Y chromosome. Y-linked genes have a transmission pattern of father to son. Traits controlled by Y-linked genes are very rare and usually involved in male-specific development.

MCQs on Inheritance

Q1. How many maximum types of gametes can be obtained when an individual has two heterozygous pairs (AaBb)?

Option 1: 2

Option 2: 3

Option 3: 4

Option 4: 9

Correct answer: 3) 4

Explanation:

The formula 2n, where n is the number of heterozygous pairs, is used to determine the maximum number of distinct gamete types that can be created when a person possesses two heterozygous gene pairs, represented as AaBb. Since n equals 2, the calculation in this case produces 22, which means that there are four potential gametes. From each gene pair, these gametes can appear in four different allele combinations: AB, Ab, aB, and ab.

Hence, the correct answer is option 3) 4.

Q2. The production of gametes by the parents, the formation of zygotes, the F1 and F2 plants, can be understood from a diagram is called:

Option 1: Bullet square

Option 2: Punch square

Option 3: Punnett square

Option 4: Net square

Correct answer: 3) Punnett square

Explanation:

The Punnett square is a diagrammatic tool used to predict the genotypes of offspring resulting from a particular genetic cross or breeding experiment. It was developed by Reginald C. Punnett in 1905. The square helps biologists determine the probability of an offspring inheriting specific genotypes by organising the potential genetic contributions from both parents. Each parent’s alleles are represented along the top and side of the square, and the possible combinations of alleles are filled in the grid to show all potential genotypes for the offspring. This tool is especially useful in Mendelian genetics to understand inheritance patterns.

Hence, the correct answer is option 3) Punnett square

Q3. Assertion: The monohybrid cross is used to study the inheritance of a single gene.

Reason: Mendel's experiments on pea plants showed that traits were inherited predictably.

Option 1: Assertion and Reason are both true, and Reason is an accurate account of Assertion.

Option 2: Both Assertion and Reason are accurate, but Reason does not adequately explain Assertion.

Option 3: The assertion is correct, but the reasoning is incorrect.

Option 4: Both the Assertion and the Reason are incorrect.

Correct answer: 1) Assertion and Reason are both true, and Reason is an accurate account of Assertion.

Explanation:

Mendel's experiments on pea plants showed that the inheritance of traits was determined by the transmission of genes from parents to offspring. He conducted a series of experiments that involved crossing plants with different traits, such as tall and short plants. By analysing the traits of the offspring, Mendel was able to determine that each trait was controlled by a pair of factors or genes and that these genes were passed down from parents to offspring in a predictable manner.

Hence, the correct answer is option 1)Assertion and Reason are both true, and Reason is an accurate account of Assertion.

Also Read:

• MCQ Practice on Inheritance

• Test Cross

• Molecular Basis of Inheritance

Recommended Video on Inheritance Definition