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Understanding the ABC Model of Flower Development

The ABC model is a genetic model that explains how different classes of genes control the formation of floral organs (sepals, petals, stamens, and carpels) in angiosperms (flowering plants). According to this model:

• A-class genes control sepals.

• A + B-class genes control petals.

• B + C-class genes control stamens.

• C-class genes alone control carpels.

These gene classes work in a combinatorial manner to define the identity of each floral whorl.

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Which Domain Characterizes ABC Model Genes?

Let’s evaluate the options:

1. C box

• Not a domain associated with floral development.

• More common in promoter elements, not structural protein domains.

• Incorrect Answer

2. MADS box

• MADS box genes are transcription factors that play a crucial role in flower development.

• The ABC genes (like APETALA1, APETALA3, PISTILLATA, AGAMOUS) are all MADS box genes.

• They bind to DNA and regulate the expression of other genes necessary for floral organ specification.

• Correct Answer

3. WRKY

• WRKY domain transcription factors are involved in plant stress responses and defense regulation, not flower organ identity.

• Incorrect Answer

4. NAC

• NAC domain proteins are involved in a wide range of functions including senescence, secondary wall formation, and abiotic stress responses, but not flower organ formation.

• Incorrect Answer

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What is the MADS Box?

• The MADS box is a highly conserved DNA-binding domain found in a family of transcription factors.

• The name comes from MCM1 (yeast), AGAMOUS (Arabidopsis), DEFICIENS (snapdragon), and SRF (human).

• MADS box genes bind to CArG box motifs in the promoters of target genes and regulate transcription during floral meristem and organ identity formation.

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Correct Answer:

2. MADS box

The MADS box domain is the defining feature of transcription factors involved in the ABC model of flower development, making it the correct answer to this question.