What is the Principle of Inheritance and Variation? Biology Note Class 12
Principle of Inheritance and Variation
What is Heredity?
Heredity is a mechanism of transfer from parents to their offspring of inherited characteristics. The field of biology concerned with inheritance and variation concepts and mechanisms is genetics. Inheritance is the basis of heredity, and characteristics are passed down from the parents to the offspring by this process.
A heredity is a form of transmission, through asexual reproduction or sexual reproduction, of traits from parents to their offspring. These features or characteristics are found in the form of genes on the chromosomes.
Genes, found on chromosomes, are the fundamental unit of inheritance, variation always occurs between individuals of one species. Variation is due to the genes found on chromosomes crossing over, recombination, mutation, and environmental influences on the expression.
Principle of Inheritance and Variation
What is Inheritance? What is a variance?
Inheritance is the method of passing characters from parent to offspring. It is the cornerstone of genetics. Variation is the degree to which descendants differ from their ancestors. In terms of anatomy, physiology, cytology, and behavioural characteristics of individuals belonging to the same species, variation may be possible. Variations occur as a result of Gene/chromosomes reshuffling. Over crossing or recombination
The inheritance includes the transition from parents to offspring of distinct inheritance groups or chromosomes. A scientist found that it was either dominant or recessive for paired pea traits. Dominant traits were often seen in the progeny when pure-bred parent plants were cross-bred, whereas recessive traits were concealed before self-pollinating was left to the first-generation (F1) hybrid plants.
Who was Mendel? What were his experiments?
Gregor Mendel, who lived in the 1800s, was an Austrian scholar, teacher, and Augustinian prelate. While living in a monastery, he worked on garden pea hybrids and is regarded as the founder of modern genetics.
Garden pea experiments were carried out by Mendel. He took 14 real-breeding pea plants with seven distinguishable characters that had two opposite characteristics. He referred to genes as “factors” that go from parents to offspring. Genes are called ‘alleles,’ which code for a pair of opposite characteristics.
What are the different laws of heredity?
Law of Dominance: One of the alleles is dominant and in the case of the heterozygote, is reflected in the phenotype, e.g. we get all the tall plants with the genotype Tt in the offspring when we cross homozygous tall (TT) and dwarf (tt) plants, so tallness is a dominant trait over the dwarfness.
Law of Gene Segregation: At the time of gamete formation, each allele separates during meiosis. There is no mixing and various gametes are transferred to characters. Only one form of gametes is produced by homozygotes and different forms of gametes are produced by heterozygotes.
Independent Assortment Law: This states that alleles are separately inherited for various traits. He showed that a dihybrid cross was used.
Test Cross: It is to discover the dominant genotype of the plant by the plant being crossed with the recessive homozygote. The two findings are: if only the dominant feature is indicated by the phenotype of offspring, then the parent plant was homozygote to the dominant feature. If both phenotypes of the offspring are produced, then the parent plant was heterozygote to the dominant feature
The popularity of Mendel was also attributed to his careful preparation and working style, learning only one character at a time.To stop cross-pollination with unwanted pollen grains, he used all available techniques. In order to evaluate the results obtained by him, he applied math and statistics. For his hybridization experiments, Mendel picked 7 contrasting garden pea characters.
Must read – What is DNA?
What is incomplete Dominance?
If none of the two alleles is dominant, neither of the parents resembles the phenotype of the heterozygote. Intermediate or a combination of the characteristics of two parents are represented by the heterozygote
Example: Inheritance of the snapdragon flower color (dog flower). We obtain all pink flowers in the F1 generation when crossing true breeding red (RR) and white flower (rr).
What is Co-Dominance?
When all the alleles in an organism express themselves together, they are said to be co-dominant. Example: ABO blood group inheritance in humans is regulated by the gene I. The I gene has three types of allelic, IA, IB, and i. In a human being, there are two out of three alleles with IA and IB coding for different forms of sugar polymers on the RBC surface.
What are the essential properties of the inheritance theory of chromosomes?
i. There are both chromosomes and genes in all the pairs in diploid cells
ii. There is only one chromosome of a specific type and only one of the two alleles of a character in a Gamete
iii. Fertilization recovers the state of the diploid
iv. At the time of meiosis, homologous chromosomes split apart
v. Chromosomes are isolated and sorted separately
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