The Mendelian principle which has always stood true is

Options

A. The law of independent assortment
B. The law of segregation
C. The law of dominance
D. All the above

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks which Mendelian principle has always been true. We need to evaluate the three principles proposed by Mendel: the law of independent assortment, the law of segregation, and the law of dominance.

2. **Evaluating the Law of Independent Assortment**: This law states that different genes independently separate from one another when reproductive cells develop. However, this law is not universally applicable due to the phenomenon of linkage, where genes that are located close to each other on a chromosome tend to be inherited together. Therefore, this law does not always hold true.

3. **Evaluating the Law of Segregation**: This law states that during the formation of gametes, the two alleles for a trait segregate from each other so that each gamete carries only one allele for each gene. This principle has been consistently observed in genetic studies, and there are no known exceptions to this law. Thus, it can be considered universally true.

4. **Evaluating the Law of Dominance**: According to this law, in a heterozygote, one allele may conceal the presence of another. However, there are exceptions such as co-dominance (where both alleles are expressed) and incomplete dominance (where the phenotype is a blend of both alleles). Therefore, this law is also not universally true.

5. **Conclusion**: After evaluating all three laws, we find that the law of segregation is the only Mendelian principle that has consistently stood true without exceptions. Thus, the correct answer is the law of segregation.

**Final Answer**: The Mendelian principle which has always stood true is the law of segregation.

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