Mendelism and Blending Inheritance | Animal Husbandry & Veterinary Science Optional for UPSC PDF Download

Mendelism and Blending Inheritance

Essence of Mendelism

• Genes are present in pairs, maintaining their identity across generations.
• Genes do not blend but exist independently.
• During reproduction, each parent passes on only one gene from each pair to offspring.

Laws of Inheritance

• Offspring receive a sample of half of the parent's inheritance.
• Sampling nature allows for transmission of different inheritances to different offspring.
• Chance governs the sampling process, ensuring each sample contains one gene of each pair.

Gene Transmission

• Offspring may receive exact duplicates of genes from one parent but opposite members from the other parent.
• For homozygous gene pairs, the transmitted gene does not affect the result.
• Heterozygous parents lead to varied gene transmission, explaining non-identical pedigrees.

Role of Dominance

• Dominance increases population variability and masks genotypic differences.
• Dominant genes do not inherently increase in number over recessive genes.
• Gene ratios remain stable in the absence of selection, with minor variations due to sampling.

Mechanism of Inheritance

• Mendelism's mechanism does not alter gene ratios significantly without selection pressure.
• Sampling variation occurs during segregation, influencing gene ratios in each generation.
• These variations are minor, especially in larger populations.

Linkage and Inheritance

• Inheritance is a complex process influenced by the linkage of genes, which can hinder genetic progress by preventing desired and undesired genes from combining freely during gamete formation.
• Mendel, the pioneer in genetics, was unaware of sex linkage, which is an exception to the principle that genetic inheritance equally originates from both parents.
• Some instances of non-Mendelian inheritance were later found to conform to Mendelian patterns upon more in-depth analysis, suggesting that the complexity of genetic factors or interactions can obscure traditional inheritance patterns.
• Selection within pure genetic lines suggests that there is minimal blending inheritance, supporting the Mendelian model of distinct gene inheritance.

Importance of Maintaining Genetic Variability

• The Mendelian mechanism of inheritance plays a crucial role in preserving genetic variation within populations, ensuring a steady level of variability over extended periods.
• This mechanism contrasts sharply with the blending theory of inheritance, which predicts a rapid convergence towards uniformity in populations over successive generations.

Impact of Mendelism on Evolutionary Theory

• Initial skepticism towards Darwin's theory of evolution stemmed from the belief in blending inheritance, which implied that natural selection had to act swiftly and perfectly to preserve new variations.
• The advent of Mendelian genetics dispelled the notion of blending inheritance and highlighted the role of individual genetic variation in evolution.
• Understanding Mendelism has reduced the emphasis on frequent mutations in breeding practices and debunked the idea that selection must immediately capitalize on variations to prevent their loss.
• Mendelism complements Darwinian theory by demonstrating the stability of populations through the accumulation of individual variations, thereby reinforcing the concept of natural selection.