Problem 7 - Biology: Concepts and Applications

Question

The stage of meiosis that makes descendant cells haploid is _____________. a. prophase I d. anaphase II b. prophase II e. metaphase I c. anaphase I f. metaphase II

Step-by-Step Solution

Answer

The correct answer is c. anaphase I.

Step 1: Understanding Meiosis

Meiosis is a type of cell division that reduces the chromosome number by half, producing four haploid cells, each genetically distinct from the parent cell. This process is crucial in sexual reproduction.

Step 2: Identifying Key Stages of Meiosis

Meiosis consists of two successive divisions: meiosis I and meiosis II. Meiosis I is the reductional division where the chromosome number is halved, while meiosis II is the equational division, similar to mitosis.

Step 3: Focus on Meiosis I

In meiosis I, homologous chromosomes are separated. The stages include prophase I, metaphase I, anaphase I, and telophase I. Anaphase I is particularly important as it is when homologous chromosomes are pulled to opposite poles.

Step 4: Understanding Haploid Cell Formation

During anaphase I, the separation of homologous chromosomes results in cells with half the number of chromosomes, making them haploid. Each cell contains only one chromosome from each pair.

Step 5: Conclusion

Since anaphase I is the stage where homologous chromosomes are separated, resulting in haploid cells, it is the correct answer.

Key Concepts

Haploid Cells

Haploid cells are a fundamental concept in genetics and are a product of the biological process known as meiosis. These cells contain half the number of chromosomes compared to diploid cells. Diploid refers to a cell that has two complete sets of chromosomes, one from each parent. In contrast, haploid cells have only one set, making them essential for sexual reproduction. They ensure that when two haploid cells (like sperm and egg in animals) unite during fertilization, the resulting zygote maintains the correct number of chromosomes.

The formation of haploid cells occurs during a specific stage of meiosis. This process involves two rounds of cell division, meiosis I and meiosis II, ultimately resulting in four non-identical daughter cells, each with a haploid set of chromosomes. The transition from diploid to haploid is crucial as it maintains the chromosomal integrity across generations, allowing for genetic diversity while preventing abnormal chromosomal numbers in offspring.

Haploid cells are vital in organisms' life cycles and convey the genetic variability necessary for evolution and adaptation. Meiosis, by creating haploid cells, provides the basis for these complex biological processes.

Anaphase I

Anaphase I is a critical phase in meiosis, particularly in meiosis I, often termed the reductional division. During this stage, several key changes occur which lead to the production of haploid cells.

• Homologous chromosomes, which are pairs of chromosomes containing the same genes inherited from each parent, are separated and pulled towards opposite ends of the cell.
• This movement is orchestrated by the spindle fibers extending from the centrioles at either pole of the cell. These fibers attach to chromosomes and aid in their separation.

The distinguishing feature of anaphase I is the segregation of homologous chromosomes rather than sister chromatids (which occurs later in meiosis II). This separation is what reduces the chromosomal number by half, setting up the production of haploid cells by the end of meiosis.

By ensuring that each resulting cell receives only one chromosome from each homologous pair, anaphase I plays a pivotal role in maintaining genetic variety and enabling successful sexual reproduction. It's this precise coordination and splitting that lay the groundwork for genetic reshuffling, contributing to the diversity seen in every generation.

Reductional Division

Reductional division is a term that aptly describes meiosis I. This phase is characterized by a reduction in the number of chromosomes, transforming a diploid cell into two haploid cells, a process vital for sexual reproduction.

Unlike mitosis, where the chromosome number remains constant as cells divide, reductional division involves a halving of the chromosomal count. This occurs because each daughter cell receives only one chromosome from each homologous pair, resulting in haploid cells.

• This ensures that sexual reproduction, which fuses two haploid cells (e.g., sperm and egg), doesn't double but maintains the species-specific chromosome number.
• Reductional division allows for the mixing of parental chromosomes, which is central to genetic diversity. This mixing is further enhanced by processes such as crossing over, where homologous chromosomes exchange genetic material during prophase I of meiosis.

Ultimately, reductional division is a key evolutionary strategy for maintaining genetic stability while facilitating adaptation through diversity. Its role in meiosis underscores the balance between conserving identity through stable chromosome numbers and promoting variability through genetic combinations.