7. What is outcome after single crossover between chromosomes having pericentric inversion and normal?
(1) Segmental Deletion and Duplication
(2) Bridge formation
(3) Ring formation
(4) Acentric and dicentric chromosomes

Concept

• Pericentric inversion: the inverted segment includes the centromere.

• In a heterozygote, homologous chromosomes pair by forming an inversion loop.

• A single crossover within this loop exchanges unequal segments because the arms differ in length and gene order.

• The result:

  • Two chromatids are parental (one normal, one inverted).

  • Two recombinant chromatids carry extra material (duplication) on one arm and missing material (deletion) on the other arm.

  • These unbalanced chromatids usually lead to inviable gametes or abnormal zygotes.

Therefore, the characteristic outcome is segmental deletion and duplication.

Option-wise explanation

1. Segmental Deletion and Duplication – correct

   • Exactly matches the recombinant products of a single crossover within a pericentric inversion loop.

   • No acentric or dicentric chromatids are formed because each recombinant still has exactly one centromere.

2. Bridge formation

   • Refers to the dicentric bridge seen at anaphase I in paracentric inversions, not pericentric ones.

   • In pericentric inversions, centromeres are not pulled to opposite poles on a single chromatid, so no bridge forms.

3. Ring formation

   • Rings are associated with ring chromosomes or with certain translocation/inversion configurations, but a simple single crossover in a pericentric inversion does not give a ring.

4. Acentric and dicentric chromosomes

   • Again characteristic of paracentric inversion crossovers: one recombinant chromatid lacks a centromere (acentric) and another has two (dicentric).

   • In a pericentric inversion, each recombinant still carries one centromere; the problem is unbalanced duplication/deletion, not loss or doubling of centromeres.

So, for a single crossover between a pericentric inversion chromosome and its normal homolog, the key outcome is segmental deletion and duplication (option 1).