Problem 96 - Objective Biology for NEET

Question

In meiosis I, the centromere undergoes (a) No division (b) Division between anaphase and interphase (c) Division between prophase and metaphase (d) Division but the daughter chromosomes do not separate

Step-by-Step Solution

Answer

The correct answer is (c) Division occurs between prophase and metaphase.

Step 1: Understand Meiosis I

Meiosis I is the first part of the meiosis process, where reduction division occurs. This process has multiple phases, specifically Prophase I, Metaphase I, Anaphase I, and Telophase I.

Step 2: Analyze each option

Option a suggests no division of the centromere in Meiosis I, which contradicts with the process's purpose - the separation of homologous chromosomes. Options b and c mention division between phases, but the centromere division specifically occurs only during one phase: Anaphase I. Finally, option d proposes division but no separation of daughter chromosomes. This contradicts with the purpose of Anaphase I where the daughter chromosomes separate after the centromere division.

Step 3: Conclude

Knowing the characteristics of each stage of Meiosis I, we can rule out options A, B and D. The centromere undergoes division in Anaphase I (not between phases), and the daughter chromosomes do separate post this division.

Key Concepts

Centromere

The centromere is a crucial part of a chromosome that plays a pivotal role during cell division. It is the region where two sister chromatids are held together, and it is also the attachment site for spindle fibers during mitosis and meiosis. In the context of meiosis, specifically, the centromere ensures that chromosomes are properly aligned and that each daughter cell receives the correct set of chromosomes.

• Holds sister chromatids together
• Serves as an attachment point for spindle fibers
• Vital for proper chromosome alignment and separation

By maintaining the integrity and correct distribution of genetic material, the centromere ensures successful cell division and genetic variability across generations.

Anaphase I

Anaphase I of Meiosis is a crucial stage where significant changes occur in the cell. During this phase, the homologous chromosomes are pulled apart to opposite poles of the cell by the spindle fibers. It is important to note that in Anaphase I, the centromeres do not divide as they do in mitosis. Instead, it is the homologous pairs that are separated.

• Separation of homologous chromosomes
• Movement towards opposite poles
• Centromeres do not divide here

This separation reduces the chromosome number by half, setting the stage for genetic diversity through the formation of non-identical gametes.

Homologous Chromosomes

Homologous chromosomes are pairs of chromosomes containing the same genes, one inherited from each parent. In Meiosis I, these pairs line up and exchange segments through crossing over, which increases genetic variability. During Anaphase I, homologous chromosomes are separated into different cells.

• Contain identical gene sequences
• One chromosome per pair from each parent
• Undergo crossing over for genetic diversity

The separation of these chromosomes during Anaphase I is vital for ensuring that daughter cells end up with a single set of chromosomes, ready for further division.

Reduction Division

Reduction division is another term for meiosis, highlighting a key feature of this process - the reduction of chromosome number by half. This is achieved during the first division of meiosis (Meiosis I), where homologous chromosomes are separated. Reduction division ensures that each gamete contains only half of the original number of chromosomes, a critical factor for maintaining species stability during sexual reproduction.

• Chromosome number is halved
• Achieved by separating homologous chromosomes
• Essential for genetic stability and diversity

This reduction in chromosome number across gametes maintains the somatic cell chromosome number in offspring after fertilization, ensuring continuity and variation within a species.