Question

What is the principal difference between meiotic anaphase I and meiotic anaphase II?

Short answer

The principal difference is that in meiotic anaphase I, homologous chromosomes are separated, while in meiotic anaphase II, sister chromatids are separated.

Step-by-step solution

Understanding Anaphase in Meiosis

Comprehend the process of meiosis, which is a type of cell division that reduces the chromosome number by half, producing four haploid cells. Anaphase is a critical stage in meiosis where chromosomes or chromatids are separated and move towards opposite poles of the cell.

Examining Meiotic Anaphase I

Recognize that during anaphase I, homologous chromosomes are separated. These are chromosomes that are similar in size, shape, and genetic content. In this phase, one chromosome from each homologous pair is pulled to opposite ends of the cell, ensuring each daughter cell receives a mix of chromosomes from both parents.

Inspecting Meiotic Anaphase II

Understand that during anaphase II, sister chromatids are separated. Anaphase II is similar to anaphase of mitosis. Here, the sister chromatids that were previously copied before meiosis began are now split and move to opposite poles of the cell.

Distinguishing Between the Two Phases

Note the principal difference: In meiotic anaphase I, homologous chromosomes are separated, whereas in meiotic anaphase II, sister chromatids are separated. This distinction is crucial for understanding the genetic variation produced by meiosis.

Key concepts

Meiosis Cell Division

Meiosis is a specialized form of cell division that is integral to the production of gametes, such as sperm and egg cells, in sexually reproducing organisms. It consists of two sequential divisions called meiosis I and meiosis II.

During this process, a single cell divides twice to produce four cells containing half the original amount of genetic information. These cells are known as haploid cells, each with just one set of chromosomes, in contrast to the diploid cells from which they originate, which contain two sets of chromosomes.

• Meiosis I reduces the chromosome number by separating homologous chromosomes.
• Meiosis II resembles mitosis and separates the sister chromatids.

This sequence of divisions is essential for sexual reproduction because it ensures that each parent contributes half of the genetic material to the offspring, which is key for genetic diversity.

Separation of Homologous Chromosomes

The first division of meiosis, meiosis I, particularly during anaphase I, deals with the separation of homologous chromosomes. Homologous chromosomes are pairs of chromosomes, one inherited from each parent, that carry the same genes in the same order but can have different alleles.

• During anaphase I, spindle fibers attach to the paired homologous chromosomes.
• These chromosome pairs are then pulled apart and moved to opposite poles of the cell.

The separation of homologous chromosomes is a vital step because it halves the chromosome number and contributes to genetic variation by creating new combinations of genes.

Separation of Sister Chromatids

Following the first meiotic division, the cell undergoes another division, meiosis II, which resembles mitosis. Anaphase II of meiosis is when sister chromatids are separated. Sister chromatids are identical copies of each other that result from the DNA replication process.

• Each chromosome lines up at the equator of the cell during metaphase II.
• In anaphase II, the sister chromatids are pulled apart by spindle fibers and migrate to opposite poles of the cell.

The result of this division is the segmentation of the previously duplicated genetic material into distinct cells, ensuring each gamete contains only one set of chromosomes.

Genetic Variation

Genetic variation is the cornerstone of biodiversity and is critically important for the survival and adaptation of species. Meiosis contributes significantly to genetic variation in several ways.

• In meiosis I, during prophase I, homologous chromosomes undergo a process known as 'crossing over' where they exchange genetic material, creating new combinations of genes.
• The independent assortment of chromosomes in meiosis I contributes to the variation because the way in which chromosomes are distributed to daughter cells is random.
• The separation of homologous chromosomes and sister chromatids during anaphase I and II, respectively, further ensures that each gamete is genetically distinct.

These mechanisms guarantee an extensive range of genetic combinations in offspring, contributing to the genetic diversity of populations.