62. The control of flowering is a complex process involving several key regulatory genes. Some statements on flower development are given below:
    A. Two major types of genes regulate floral development: meristem identity genes and floral
    organ identity genes.
    B. The important genes in Arabidopsis that play key regulatory roles in meristem identity are: APETALA1, LEAFY and SUPPRESSOR OF CONSTANS1.
    C. The genes that determine floral organ identity were discovered as floral homeotic mutants.
    D. Most plant homeotic genes belong to a class of related sequences known as FAD box genes.
    Which one of the following combinations of the above statements is correct?
    (1) A, B and C (2) B, C and D
    (3) A, C and D (4) A, B and D

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Introduction

The ABC model of floral organ development in Arabidopsis defines spatially regulated gene expression patterns that produce distinct floral organs. Class A genes—APETALA1 (AP1) and APETALA2 (AP2)—specify floral sepals and petals, providing the foundation for flower morphology. AP2 is uniquely expressed during sepals and petals formation.

Expression Patterns of Floral Homeotic Genes

• APETALA2 transcripts localize primarily to the first two floral whorls, which give rise to sepals and petals.

• APETALA1 (AP1) works together with AP2 and also contributes to early floral meristem identity.

• AGAMOUS (AG), a Class C gene, is expressed in the inner floral whorls: stamens and carpels, not during sepal and petal formation.

• APETALA3 (AP3), a Class B gene, is expressed in second and third whorls (petals and stamens), but not sepals.

Evaluation of Statements

1. AP2 expression during sepal and petal development is correct, confirming its Class A role.

2. AGAMOUS is not a Class A gene but Class C.

3. AP1 is not expressed during carpel development.

4. AP3 is not expressed during sepal development.

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Summary Table: Gene Expression by Floral Whorls

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Conclusion

APETALA2 transcripts are expressed during sepal and petal formation consistent with Class A gene function, making option (1) correct.