Question

Meiosis occurs in (a) Haploid cells (b) Diploid cells (c) Both haploid and diploid cells (d) Triploid cells

Short answer

The correct answer is (b) Diploid cells

Step-by-step solution

Understand the process of meiosis

Meiosis is a unique type of cell division that occurs in sexually reproducing organisms. It reduces the chromosome number by half and produces four genetically unique haploid cells. It begins in a parent cell that is diploid, meaning it has two sets of chromosomes.

Analyze the options

Given that meiosis begins in a diploid cell, options (a) haploid cells and (d) triploid cells can be eliminated because haploid cells have a single set of chromosomes, and triploid cells, which have three sets of chromosomes, are usually sterile because they can't undergo regular meiosis.

Choose the correct answer

Since the process of meiosis only occurs in diploid cells, the correct answer would be (b) Diploid cells as these are the cells which are able to undergo meiosis.

Key concepts

Meiosis

Meiosis is a specialized form of cell division crucial for sexual reproduction in eukaryotes. The process serves to reduce the chromosome number by half, from diploid to haploid, ensuring that offspring have the same number of chromosomes as each parent. Unlike mitosis, which results in two identical daughter cells, meiosis consists of two sequential cell divisions—meiosis I and meiosis II—ultimately producing four non-identical haploid gametes.

During meiosis I, homologous chromosomes—each consisting of two sister chromatids—pair up and exchange genetic material through a process called crossing over. This genetic recombination increases genetic diversity. Meiosis II resembles mitotic division, where the sister chromatids separate. The ultimate result is four genetically diverse haploid cells, each with half the number of chromosomes of the original diploid cell.

Diploid Cells

Diploid cells contain two complete sets of chromosomes, one set inherited from each parent. These cells form the majority of an organism's body, known as somatic cells. A diploid number, often represented as 2n, varies between species; for example, humans have 46 chromosomes or 23 pairs.

These cells are crucial for sexual reproduction because they give rise to gametes—sperm and eggs in animals—through the process of meiosis. Diploidy enables genetic variation and contributes to the robustness of an organism by masking deleterious mutations that might be expressed in a haploid state. Recognizing the diploid origin of gametes can help students appreciate the interplay between inheritance and variation which is fundamental to the study of biology.

Cell Division

Cell division is the process by which a parent cell divides into two or more daughter cells. It is a fundamental aspect of the life cycle of cells, allowing for growth, reproduction, and repair of organisms. There are two main types of cell division: mitosis and meiosis.

Mitosis

During mitosis, a single cell divides to produce two genetically identical daughter cells, used for growth and asexual reproduction within an organism.

Meiosis

In meiosis, which is another form of division, the resultant cells have half the chromosome number (haploid) of the parent cell and are used in sexual reproduction to produce a new organism when two haploid gametes fuse. Emphasizing these differences can clarify for students when and why each type of cell division occurs.

Sexual Reproduction

Sexual reproduction is a biological process where two haploid gametes—a male sperm and a female egg—combine to form a diploid zygote. This fusion, known as fertilization, initiates the development of a new organism with genetic material from both parents.

The distinct feature of sexual reproduction is the combination of genetic material from two different cells, which leads to genetic variation among offspring. Such variation is beneficial as it contributes to the adaptability and evolution of species. In this context, students should understand that meiosis is the cellular basis for sexual reproduction, providing the mechanism for creating diverse gametes necessary for this type of reproduction.