• A. Linkage of genes
• B. Unit factors in pairs
• C. Dominance/Recessiveness
• D. Monohybrid cross
• E. Segregation

Choose the correct answer from the options given below:

1. A, B, E only
2. C, D, A only
3. B, C, E only
4. A, B, D, E only

   Correct Answer: Option 3 (B, C, E only)

   Mendel’s first three postulates are the foundational principles from his pea plant experiments: unit factors in pairs (B), dominance/recessiveness (C), and segregation (E). These form the core of classical genetics before linkage or independent assortment.

   Postulate Analysis

   Mendel’s postulates establish how traits are inherited:

   • B. Unit factors in pairs: Each trait controlled by paired hereditary units (alleles); one from each parent.​

   • C. Dominance/Recessiveness: In heterozygotes, one allele masks the other (complete dominance).​

   • E. Segregation: Allele pairs separate during gamete formation; each gamete gets one allele.​

   Not included: A (linkage – discovered later by Morgan), D (monohybrid cross – experimental method, not postulate).

   Option Breakdown

   Option	Includes	Excludes	Issue	Correct?
   1	A, B, E	C	Adds linkage (not Mendel’s)	No
   2	C, D, A	B, E	Includes cross method + linkage	No
   3	B, C, E	A, D	Exact three postulates	Yes
   4	A, B, D, E	C	Too many; adds linkage + method	No

   Historical Context

   Mendel proposed these in 1866:

   1. Paired unit factors (B)

   2. Dominance principle (C)

   3. Segregation law (E)

   Independent assortment (4th) came from dihybrid crosses.

   ---

   Introduction to Mendel’s First Three Postulates

   Mendel’s first three postulates form the bedrock of genetics: unit factors in pairs (B), dominance/recessiveness (C), and segregation (E). NEET Q.70 tests precise recall excluding later discoveries like linkage. These principles explain monohybrid 3:1 ratios.​

   Detailed Postulate Explanations

   1. Unit Factors in Pairs (B)

   • Each trait controlled by two alleles (one maternal, one paternal)

   • Organisms diploid: homozygous (AA) or heterozygous (Aa)

   • Mendel’s insight: Inheritance particulate, not blending

   2. Dominance/Recessiveness (C)

   • Dominant allele expresses in heterozygote (Aa → A phenotype)

   • Recessive allele masked but unchanged

   • Explains F1 uniformity, F2 3:1 ratio

   3. Segregation (E) – Law of Segregation

   • Alleles separate during meiosis

   • Each gamete gets one allele randomly

   • Genotypic ratio F2: 1 AA : 2 Aa : 1 aa

   Why Other Options Wrong

   • Linkage (A): Morgan 1910, not Mendel

   • Monohybrid cross (D): Experimental technique, not postulate

   • Only B+C+E = first three postulates

   NEET Memory Aid

   “BCE” = Basic Characters Equal (paired factors, complete dominance, equal segregation)

   Punnett square verification:

   text

   A a
A AA Aa
a Aa aa


   3 dominant : 1 recessive phenotype confirms all three postulates working together.

   Exam Strategy

   • Recognize “first three” excludes Independent Assortment (dihybrid)

   • Postulates = principles; crosses = methods

   • B,C,E sequence matches Mendel’s publication order