26. A reciprocal translocation heterozygote at the end of meiosis I generate
(1) An acentric and a dicentric chromosome
(2) Viable gametes with deletions and duplications
(3) Viable gametes with only parental type chromosomes
(4) All non-viable gametes

Concept in brief

• In a reciprocal translocation heterozygote there are two normal chromosomes and two translocated derivatives.

• During meiosis I they form a quadrivalent (cruciform) pairing structure.

• Alternate segregation sends either both normal chromosomes or both translocated chromosomes to a pole → balanced gametes (viable).

• Adjacent segregations give unbalanced combinations with duplications and deletions → mostly non‑viable gametes.

• So the viable gametes are those carrying only parental-type chromosome sets (normal or balanced translocation), not recombinant or unbalanced ones.

Option-wise explanation

1. An acentric and a dicentric chromosome

   • This is typical of a paracentric inversion crossover, not of a reciprocal translocation.

   • Reciprocal translocations keep one centromere per chromosome; the problem is unbalanced segment content, not acentric/dicentric chromatids.

2. Viable gametes with deletions and duplications

   • Gametes carrying sizable deletions/duplications are usually unbalanced and non‑viable or cause severe abnormalities.

   • In translocation carriers, these are the gametes that are typically eliminated, so this is incorrect.

3. Viable gametes with only parental type chromosomes – correct

   • “Parental type” here means either the normal chromosome pair or the balanced translocated pair produced by alternate segregation.

   • These have a complete, balanced genome and thus are the viable gametes from a translocation heterozygote.

4. All non‑viable gametes

   • Not true; if all gametes were non‑viable, carriers could not reproduce, but many balanced carriers are phenotypically normal and fertile (though with increased risk), proving that some gametes are viable.

Hence, the correct description of what a reciprocal translocation heterozygote generates at the end of meiosis I is viable gametes with only parental-type chromosomes (option 3).