Question

Assertion: Meiosis produces four genetically dissimilar cells. Reason: Crossing over or gene exchange takes place in meiosis.

Short answer

Yes, the assertion is correct and the reason is the right explanation. Meiosis does produce four genetically dissimilar cells primarily due to the crossing over or gene exchange.

Step-by-step solution

Understanding Meiosis

Understand that meiosis is a type of cell division that reduces the number of chromosomes in a parent cell by half and produces four gamete cells (sex cells). This process is fundamental to sexual reproduction and leads to genetic diversity.

Role of Crossing Over

Learn that crossing over is a process during meiosis where two chromosomes pair up and exchange segments of their genetic material. This creates new combinations of genes, contributing to genetic diversity in offspring.

Linking Assertion and Reason

Assert that indeed, meiosis produces four genetically dissimilar cells, primarily due to the exchange of genetic material during the 'crossing over' phase. This confirms that the reason correctly explains the assertion.

Final Statement

Formulate the final statement connecting the assertion and reason: 'Meiosis produces four genetically dissimilar cells, due to the occurrence of 'crossing over' or gene exchange during one of its stages.'

Key concepts

Genetic Diversity

Genetic diversity refers to the variety of different forms of genes within a species. This diversity is the cornerstone of evolutionary adaptation and survival. One of the principal ways genetic diversity is achieved in organisms that reproduce sexually is through a process known as meiosis.

During meiosis, germ cells divide to produce unique gamete cells, each containing a different combination of DNA. This is due in part to the random assortment of chromosomes that occurs during the formation of gametes. The process ensures that each gamete has a unique set of genetic instructions, which, when paired with another gamete during fertilization, results in offspring with a genetic makeup that's different from either parent. This genetic variation is essential for a population's adaptability to changing environments and for the health of the species as a whole.

Crossing Over

Crossing over is a critical event in meiosis that significantly increases genetic diversity. It occurs during prophase I, one of the early stages of meiosis. Here, homologous chromosomes — pairs of chromosomes containing the same genes but different alleles, or versions of those genes — come together and exchange genetic material.

How Crossing Over Works

• Homologous chromosomes pair up along their lengths.
• At points called chiasmata, the arms of the chromosomes cross over each other.
• Genetic material is swapped at the crossover points.
• When the chromosomes separate, each now contains a mix of alleles from both original chromosomes.

This exchange creates new combinations of alleles on each chromosome, generating genetically unique gametes, which, when fertilized, lead to even greater variability in the offspring.

Sexual Reproduction

Sexual reproduction is a biological process by which organisms create descendants that have a combination of genetic material. Unlike asexual reproduction, where the offspring is genetically identical to the parent, sexual reproduction involves the fusion of two distinct gametes – sperm and egg cells.

For the continuation of a species, sexual reproduction offers the advantage of increased genetic diversity. This is due to the segregation and assortment of chromosomes during meiosis, and the genetic shuffling due to crossing over. The resultant genetic variation in offspring enables a population to adapt over time to environmental changes and protects against diseases that could wipe out entire populations with identical genetic profiles. Thus, sexual reproduction, underpinned by meiosis and the genetic mixing it provides, is a significant evolutionary strategy for many organisms.

Gamete Cells

Gamete cells, also known as sex cells, are specialized cells that are involved in sexual reproduction. Human gametes come in two forms: sperm for males and eggs (or ova) for females. These cells are haploid, meaning they contain half the number of chromosomes found in normal body cells, which are diploid.

Formation and Role

Through the process of meiosis, a diploid cell divides to produce haploid gametes. During fertilization, one sperm and one egg combine to form a diploid zygote, restoring the full complement of chromosomes and creating a new, genetically distinct individual. The reduction of chromosome number in gametes and their subsequent fusion during fertilization are crucial for maintaining the genetic stability of a species while simultaneously promoting genetic diversity.