48. Organ Identity genes are responsible for correct positioning of floral organs on floral meristem.
    Mutation in them will lead to
    (1) Loss of all organs from whorls
    (2) More number of organs in certain whorls
    (3) Appearance of organs at incorrect positions
    (4) No flower

Introduction

Floral organ development in angiosperms is controlled by organ identity genes, which ensure that sepals, petals, stamens, and carpels develop in their precise positions on the floral meristem. These genes encode transcription factors that regulate spatial gene expression patterns responsible for organ differentiation.

Function of Organ Identity Genes

• Organ identity genes are responsible for establishing the identity and precise positioning of floral organs in the four whorls of a flower.

• They direct the developmental programs that result in formation of sepals, petals, stamens, and carpels in their correct spatial locations.

Consequences of Mutations

• Mutations in organ identity genes do not typically cause loss of all organs or increased numbers but usually cause homeotic transformations.

• This means organs appear in incorrect positions, being replaced by other organ types (e.g., petals replaced by sepals or stamens replaced by petals).

• The classic ABC model of flower development is based on function of organ identity genes; disruption causes organ identity switches and positional errors.

Summary

Conclusion

Mutations in organ identity genes primarily cause floral organs to develop at incorrect positions rather than causing complete organ loss or overproduction, consistent with option (3).