Problem 74 - Objective Biology for NEET

Question

Meiosis is (a) Disjunctional division (b) Equational division (c) Multiplicational division (d) Reductional division

Step-by-Step Solution

Answer

The correct answer is (d) Reductional division

Step 1: Understand Meiosis

Meiosis is a type of cell division that results in four daughter cells each with half the number of chromosomes of the parent cell, as in the production of gametes and plant spores. This is crucial for sexual reproduction in living organisms.

Step 2: Determine the correct term

By comparing the provided choices with the definition of meiosis given in step 1, (d) Reductional division is the most appropriate term to describe meiosis, because meiosis reduces the number of chromosomes per cell by half.

Key Concepts

Cell Division

Cell division is a fundamental biological process whereby a parent cell divides into two or more daughter cells. It's essential for growth, repair, and reproduction in living organisms.

In multicellular organisms, cell division can occur via two primary methods: mitosis and meiosis. Mitosis results in two identical daughter cells and is key for somatic cells to proliferate. In contrast, meiosis, the focus of our textbook exercise, serves a different purpose as it produces gametes, also known as sex cells, with half the chromosomes compared to the original cell.

Understanding cell division is paramount for grasping the mechanisms behind genetic diversity and the life cycle of organisms.

Chromosomes

Chromosomes are long strands of DNA wound around proteins called histones, which exist within the nucleus of eukaryotic cells. Human cells, for instance, typically have 46 chromosomes, comprising 23 pairs.

Each chromosome carries hereditary information in the form of genes. During meiosis, chromosomes play a critical role as they undergo recombination and segregation, processes ensuring genetic diversity in offspring. Importantly, meiosis starts with cells that have a full set of chromosomes (diploid) and ends with cells that have half the number of chromosomes (haploid), which is essential for maintaining the constant chromosome number across generations in sexually reproducing organisms.

Sexual Reproduction

Sexual reproduction is a biological process where two organisms contribute genetic material to produce offspring. This process involves the fusion of gametes: the sperm from the male and the egg from the female.

The uniqueness of sexual reproduction lies in the exchange and mixing of genetic material from two parents, which increases genetic variation within a species. Genetic variety is a crucial factor in the survival and evolution of species, as it improves adaptability to changing environments. Meiosis is integral to sexual reproduction because it produces the diverse gametes necessary for this genetic exchange.

Gametes

Gametes are the special cells used by organisms during sexual reproduction to transmit genetic information to their offspring. These include sperm cells in males and egg cells in females.

Gametes are haploid, meaning they contain one set of chromosomes and unite during fertilization to form a diploid zygote, restoring the chromosome number to its original diploid state. The creation of gametes through meiosis is vital as it ensures each gamete is genetically distinct due to the reshuffling of genetic material during the process.

Reductional Division

Reductional division, the hallmark of meiosis, refers to the process by which the chromosome number is halved from diploid to haploid. During this division, homologous chromosomes are separated, leading to daughter cells that contain only one chromosome from each pair.

This is contrasted with equational division, where cells divide without altering the number of chromosomes. The reductional division is crucial in maintaining the stability of the genome across generations by ensuring that each gamete carries just a single set of genetic instructions, which are mixed at fertilization to produce genetically diverse offspring.