The passing on of genetic traits from parents to offspring is known as Inheritance in biology. It refers to the transmission of genes from one generation to another. These genes contain the genetic information which is passed on to the progeny by inheritance. Inheritance explains the similarity in the characteristics of parents and their young ones. The visible characteristic traits of heredity include similarity in eye colour, hair colour, body type, facial structure, etc. Heredity also confers hereditary diseases from parents to the progeny. Inheritance and heredity play a greater role in chromosomal anomalies in some cases.
Inheritance is a process of acquiring characteristic traits by offspring organisms from parent organisms. Inheritance is the link between organisms and evolution. Sexual reproduction causes the progeny to acquire shared inheritance. When different organisms of the same species mate, they both transfer half of their genetic information to the new individual. This causes a genetic mix-up and variation. The variations keep accumulating over a period of time and through generations causing a species to evolve. Biological inheritance is studied under genetics in biology.
Heredity is the reason why the child looks somewhat identical to its parents. Inheritance describes how heredity works. It lets us know why and how organisms of the family share similar characteristics. We began to understand the concepts of inheritance from the 19th Century. Sir Gregor Mendel conducted some experiments, postulated laws and helped know more about the concepts of heredity and inheritance.
The scientist Gregor Mendel carried out hybridization experiments on green peas in his pea garden and recorded his observations. He cross-pollinated plants with distinct characteristics and made a table of traits that were shown by the offspring plants. The natural continuous self-pollinating plants were called the true-breeding pea lines.
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Pea plants can be easily grown and require less maintenance.
They self-pollinate naturally and can even be cross-pollinated.
Being an annual plant, it will take less time and many generations of the plant can be studied in a short span.
Pea plants have many contrasting characters.
Mendel performed monohybrid cross experiments and dihybrid cross experiments on the selected pea plants.
Monohybrid Cross Experiments: In the monohybrid cross experiment, Mendel crossbred two pea plants with opposite traits. So, one tall and the other short plant was chosen. The resulting progeny or the first generation- F1 was tall with the characteristic trait from the taller plant. The F1 progeny was again cross-pollinated and the resulting progeny were tall as well as short in 3:1 ratio. The same experiment was repeated for other traits like colour, type of leaves, etc. and similar results were obtained each time. This experiment gave way for the laws of segregation and dominance.
Dihybrid Cross: In this experiment, Mendel selected two traits having two different alleles (a variant of a given gene). For the experiment, he cross-pollinated yellow and round seeds with green and wrinkled seeds and obtained the F1 generation as yellow round seeds which meant round and yellow is the dominant trait. The F1 progeny was then self-pollinated and 4 different traits were observed in the new generation of progeny. These traits were wrinkled-yellow, round-yellow, wrinkled-green seeds and round-green in the ratio 9:3:3:1.
This law gave way for the second law, the law of independent assortment.
The genetic makeup of the plant is referred to as the genotype and the physical appearance is called the phenotype.
The genes are transferred from parents to progeny in pairs called alleles.
During gametogenesis, there is 50% probability of one of the two alleles to fuse with the other parent.
Same alleles are called homozygous alleles and the different ones are termed as heterozygous alleles.
Law of Dominance: This is the first law of inheritance as per which hybrid offspring will only inherit the dominant trait in the phenotype (physical structure). Suppressed alleles are called recessive traits. The alleles that determine the phenotypic characteristics are called dominant traits.
Law of Segregation: The law of segregation put forward by Mendel, states that two copies of each hereditary factor segregate during the production of gametes and the individual acquires one heredity factor from each parent. This means, allele pairs segregate during gamete formation and reunite randomly during fertilization. This law is also known as Mendel’s third law of Inheritance.
Law of Independent Assortment: Law of independent assortment states that segregation of a pair of a trait takes place independently of the other pair at the time of gamete formation. Different traits get an equal opportunity to occur as the heredity factors of an individual assort independently. This is also Mendel’s second law of inheritance.
Q1. Define Inheritance.
Ans: Inheritance is the process of acquiring characteristic traits by offspring organisms from parent organisms. Inheritance is the link between organisms and evolution. Sexual reproduction causes the progeny to acquire shared inheritance. When different organisms of the same species mate, they both transfer half of their genetic information to the new individual. This causes a genetic mix-up and variation. The variations keep accumulating over a period of time and through generations causing a species to evolve.
Q2. What are Mendel’s Laws of Inheritance?
Ans: Mendel proposed three laws of inheritance from the conclusion drawn from his experiments with the pea plants. These are:
Law of Dominance
Law of Independent Assortment
Law of Segregation