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In biology, Inheritance refers to the process through which genetic information is passed on from parents to offspring. Subsequently, this is the reason why members of the same family tend to have similar characteristics.
The variations that are exhibited by the individuals can accumulate and they may cause a species to evolve, this all is done through Inheritance. The study of biological inheritance is known as genetics.
The visible characteristics of the inheritance involve similarity in the eye color, hair color, body type, facial structure, and so on. It also includes hereditary diseases passed on from parents to the offspring.
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Keyterms: Inheritance, Gene, Genetics, Variation, Biological inheritance, Heredity, Evolution, Organisms, Sexual reproduction, Reproduction
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Meaning of Biological Inheritance
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Inheritance refers to a process in which a child inherits the characteristics traits from his/her parents. Inheritance is also known as heredity and serves as a link between organisms and evolution. Through sexual reproduction, the progeny tends to acquire the shared inheritance.
The different organism of the same species transfers half of their genes to the new individual when they both mate. This is the reason for genetic mix-up and variation. The variations accumulate over some time and also through the generations that cause species to evolve. In biology, biological inheritance is studied under genetics.
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Experiment on Inheritance by Mendel
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The reason why the child looks identical to its parents is heredity. Due to heredity, one gets to know how the organism of the same family shares the same features. Understanding the concepts of inheritance started in the 19th century. Some experiments and postulated laws were conducted by Sir Gregor Mendel that helps us a lot in understanding and knowing more about the concepts of inheritance and heredity.
An experiment, named the hybridization experiment was carried out by the Scientist Gregor Mendel. He experimented on green peas in his pea garden and then he recorded the observations.
The scientist pollinated plants crossly with different properties and showed the traits in the table that were noticed by the offspring which were later known as the true-breeding pea lines.
Reasons for selecting the Pea plant for the Experiment
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The reasons for the selection of pea plant for the experiment are mentioned below-
- Pea plants do not require high maintenance and they can be easily grown.
- Pea plants can naturally self-pollinate, they can be cross-pollinated also.
- Since the pea plant is an annual plant, it takes less time to maintain and many generations of the pea plant can also be studied in a short period.
- It also includes many contrasting characters.
On the selected pea plant, the scientist performed a monohybrid and dihybrid cross experiment.
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- Monohybrid cross experiments- In this experiment, the scientist crossbred the plants of the opposite traits. So, one tall and one short plant was chosen. The cross-pollination of tall and short plants results in tall plants. The F1 progeny was cross-pollinated again, the progeny obtained after cross-pollination were both tall and short in the ratio of 3:1. For other traits like- color, types of leaves, and so on, the same experiment was repeated, the same result was obtained each time. Monohybrid cross-experiment gave way for the law of segregation and dominance.
- Dihybrid cross experiments- In a dihybrid cross experiment, the scientist selected two traits that have different alleles from each other. For the dihybrid cross experiment, Mendel cross-pollinated yellow and round seeds along with green and wrinkled seeds. Through the experiment, he gets F1 generation as yellow round seeds that mean round and yellow is the domain trait. After this, the F1 progeny was self-pollinated along with the observation of 4 different traits in new generations of the progeny. The traits were wrinkled-yellow, round-yellow, wrinkled-green seeds, and round-green in the ratio of 9:3:3:1.
Experiment’s Conclusions
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The conclusions of the experiment are mentioned below-
- The physical appearance of the plant is referred to as the phenotype while the genetic makeup of the plant is called genotype.
- The genes are transferred to offspring from the parents, in pairs that are known as alleles.
- During gametogenesis, the probability of one of the two alleles fusing with the other plant is 50%.
- Same alleles are referred to as homozygous and the different alleles are called heterozygous alleles.
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Mendel’s Law of Inheritance
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There are three laws of inheritance that are given by Gregor Mendel. The laws are mentioned below-
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Law of Dominance
The Law of dominance is considered as the first law of inheritance according to which the hybrid progeny will inherit the dominant trait in the physical structure only.
Recessive traits are termed suppressed alleles. The alleles determining the phenotypic characteristics are termed dominant traits.
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Law of Independent Assortment
This law tells us that the separation/segregation of a trait’s pair takes place of the other pair independently at the time of formation of the gamete.
Different traits equally get an opportunity to occur independently as the hereditary factors of an individual assort. This law is also termed Mendel’s second law of inheritance.
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Law of Segregation
The law of segregation initiated by the scientist Gregor Mendel tells us that during the formation of gametes, the two copies of each genetic element separate to ensure that each parent's offspring inherits one factor.
It means that allele pairs separate when gamete is forming and randomly reunite during fertilization. The Law of segregation is also known as Mendel’s third law of Inheritance.
Things to Remember
- Inheritance refers to a process in which a child inherits the characteristics traits from his/her parents.
- Inheritance is also known as heredity and serves as a link between organisms and evolution.
- The study of biological inheritance is known as genetics.
- The visible characteristics of the inheritance involve similarity in the eye color, hair color, body type, facial structure, and so on.
- The different organism of the same species transfers half of their genes to the new individual, when they both mate, so this is the reason for genetic mix-up and variation.
- The Mono-hybridization and Hybridization experiment was carried out by the Scientist Gregor Mendel.
- There are three laws of Mendel’s law of inheritance, namely- the law of dominance, the law of segregation, and the law of independent assortment.
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Sample Questions
Ques: What criteria are adopted for selecting the organisms to perform crosses for studying the inheritance of a few traits? (3 marks)
Ans: The criteria that are adopted for selecting the organisms are mentioned below-
- The traits should easily be visible.
- The organism must have different traits.
- The organism should have a span of short time.
- The organism must have to be true breeds.
- The process of pollination must be simple.
- The traits should be easily manipulated.
- Gametes should mate randomly.
Ques: Explain the difference of alleles of a gene from each other and also describe its importance. (2 marks)
Ans: The alternative form of the same gene is called alleles. For instance, a gene for height consists of two alleles, of which one is for tall (T) and one is for short (t). They are different in their nucleotide sequence due to which results in different phenotypes. The importance is mentioned below-
- They play a very important role in studying inheritance and its behavior pattern.
- Due to contrasting phenotypes of a character, it shows variation in the population.
Ques: How far are the genes and environment responsible for expressing a particular trait? (2 marks)
Ans: The genes remain in activity throughout our lives. It switched on and off its expression to the environment. The external factors that are responsible for the gene expression that exhibits changes in the phenotypic are light, nutrition, and temperature, etc. Experiments provide an opportunity for the expressions of the traits while the gene provides the potentiality.
Ques: Give the difference between dominance, codominance, and incomplete dominance. (2 marks)
Ans: Dominance is considered as the phenomenon in which the effects of different variants of the same gene are masked by one variant.
Co-dominance describes the relationship between two alleles of a gene, in which none of the alleles is recessive and it expresses the phenotypic of all the alleles.
Incomplete dominance is considered as the form of intermediate inheritance. In this, one allele for the specific trait is not completely expressed over its paired allele.
Ques: What do you mean by the chromosomal theory of inheritance? (2 marks)
Ans: The fundamental theory of genetics that recognizes chromosomes as the carriers of genetic materials is termed the chromosomal theory of Inheritance.
Ques: What are the characteristics of a true-breeding line? (3 marks)
Ans: The characteristics of a true-breeding line are mentioned below-
- It undertakes self-pollination.
- For several generations, it depicts stability in Inheritance.
- It produces gametes with the same traits and is used as parents for artificial hybridization.
- To identify the genotype through a test cross, homozygous recessive plants are used.
Ques: Describe the characteristics of the chromosome theory of inheritance. (3 marks)
Ans: Following are the characteristics of the chromosome theory of the inheritance-
- Diploid condition is restored by fertilization.
- They separate and assorted independently.
- At the time of meiosis, homologous chromosomes get separated.
- Both chromosomes and genes exist in the pairs of diploid cells.
- Gamete consists of only one chromosome at a particular type and only one from the two alleles of a character.
Ques: Why does color blindness mostly occur in men more than females? (2 marks)
Ans: Color blindness is the sex-linked problem associated with the X chromosomes. For affected by this disease the female should have alleles in both the X chromosomes. However, if the alleles are available only in one chromosome then, the female is considered as the carrier of the disease. Since males have only chromosomes, it can be concluded that having such alleles in one chromosome can be restricted to be closer to disease. Therefore, males have more chances to have the problem of color blindness more than females.
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