## CORE INFORMATION\n✓ **Answer**: B\n## CONCEPT FRAMEWORK\n\t**Primary Concept**: Chromosome Structure during Meiosis\n\t**Related Topics**: Homologous Chromosomes, Synapsis, Crossing Over, Meiosis I\n\t**Prerequisites**: Basic understanding of cell division and chromosome structure.\n## SOLUTION PATHWAY\n**Given Information**:\nA bivalent is being described.\n**Method & Steps**:\n1. **Definition of Bivalent**: A bivalent is a pair of homologous chromosomes that have synapsed (paired up) during meiosis I.\n Reasoning: Homologous chromosomes are similar in size, shape, and carry the same genes (but may have different alleles). They pair up during prophase I of meiosis.\n2. **Number of Chromatids**: Each chromosome in a homologous pair has replicated during the S phase prior to meiosis. Therefore, each chromosome consists of two sister chromatids.\n Working: A pair (bivalent) of homologous chromosomes means 2 chromosomes. Each chromosome has 2 sister chromatids.\n Key Point: A bivalent is formed by two homologous chromosomes, each consisting of two sister chromatids.\n3. **Total Chromatids**: Total chromatids in a bivalent = 2 chromosomes * 2 chromatids/chromosome = 4 chromatids.\n Result: 4\n Verification: The term 'bivalent' refers to two homologous chromosomes paired together. Each chromosome, having replicated, consists of two chromatids. Thus, a bivalent has four chromatids.\n## OPTION ANALYSIS\n[A] :x: '2' represents only the number of homologous chromosomes in a bivalent, not the number of chromatids.\n[B] ✓: '4' is correct because a bivalent, consisting of two chromosomes that have replicated, has four chromatids.\n[C] :x: '8' would imply four homologous chromosomes paired together, which is not the definition of a bivalent.\n[D] :x: '16' is even further off and doesn't represent any relevant structure in meiosis.\n## LEARNING AIDS\n\t**Common Mistakes**:\n\t\t1. Confusing Bivalent with the number of homologous chromosomes: Remember a bivalent is a *pair* of homologous chromosomes, and each chromosome has replicated into two sister chromatids.\n\t\t2. Forgetting replication: Meiosis I occurs after DNA replication in the S phase. Each chromosome entering meiosis already consists of two sister chromatids.\n\t**Quick Tips**:\n\t\t1. Bi = 2 (homologous chromosomes); each chromosome has 2 chromatids, so 2 x 2 = 4 chromatids.\n\t\t2. Visualize the structure: Imagine two X's joined together - each X representing a replicated chromosome, and the pair forming the bivalent. Count the arms of the X's to get the number of chromatids.

NEET Botany Cell Cycle and Cell Division MCQs

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NEET Botany Cell Cycle and Cell Division MCQs

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