Q.47 Which of the following statements are correct?

1. In complete dominance of one allele, heterozygous phenotype is same as that of homozygous dominant.
2. In codominance, both phenotypes are expressed in homozygotes.
3. In multiple allele cases, genes have more than two alleles in the population.
4. In pleiotropy, multiple gene affects single phenotypic character.

Choose the correct answer from the options given below:

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

   This Mendelian genetics MCQ tests core concepts like dominance patterns and gene effects, building on prior DNA replication questions for molecular biology mastery.

   Correct Answer: C (A and C only)

   Options A and C accurately describe dominance and multiple alleles; B misstates codominance genotype, while D reverses pleiotropy definition.

   Option A: Complete Dominance – Correct

   In complete dominance, heterozygotes (Rr) show the same phenotype as homozygous dominant (RR), like Mendel’s tall peas (TT=Tt=tall). The dominant allele fully masks recessive, producing identical traits.

   Option B: Codominance in Homozygotes – Incorrect

   Codominance expresses both alleles simultaneously in heterozygotes (e.g., AB blood type shows A+B antigens), not homozygotes (AA or BB show single types). Homozygotes can’t express “both” since they carry identical alleles.

   Option C: Multiple Alleles – Correct

   Multiple allele systems feature more than two alleles in a population (e.g., ABO blood: IA, IB, i), though individuals inherit only two. This expands phenotypic variation beyond simple dominant/recessive pairs.

   Option D: Pleiotropy Definition – Incorrect

   Pleiotropy means one gene affects multiple phenotypic traits (e.g., sickle cell allele impacts blood, spleen, bones), not multiple genes on one trait. The latter describes polygenic inheritance.

   Exam Insights

   For Mendelian genetics MCQ, distinguish: complete dominance (heterozygote = dominant homozygote), codominance (both alleles in heterozygote), multiple alleles (population-level), pleiotropy (one gene, many traits). Perfect for NEET genetics sections.