Question

Male honeybees, which are haploid, produce sperm by meiosis. Explain what unusual event (compared with other animals) must occur during spermatogenesis in honeybees to produce sperm. Does this unusual event occur during meiosis I or meiosis II?

Short answer

The unusual event in honeybees' spermatogenesis is that meiosis leads to direct production of haploid sperms, as drones are already haploid organisms. This event conceptually occurs during the meiosis II phase.

Step-by-step solution

Understanding Meiosis in Honeybees

Firstly, get a clear understanding of meiosis and spermatogenesis in honeybees. Honeybee males, or drones, are haploid organism, meaning they have only one set of chromosomes in their cells, unlike diploid organisms where cells contain two sets of chromosomes.

Identifying the Unusual Event

It is exceptional in honeybees because unlike most animals where meiosis results in four haploid cells, in honeybees it leads to production of haploid sperms directly. This is because drones are already haploid, so there's no need to reduce the number of chromosomes in half, as in other animals. Meiosis in honeybees results in four haploid sperms for every primary spermatocyte.

Determination of Meiosis Phase

Regarding the phase of meiosis during which this unusual event happens, it happens throughout the course of meiosis, both I and II, but conceptionally, it relates more to meiosis II. This is because meiosis II is the part of meiosis most associated with the creation of haploid cells in other animals.

Key concepts

Haploid Organism

A haploid organism, such as a male honeybee or 'drone', carries a single set of chromosomes in each of its cells. Unlike diploid organisms that have two sets of chromosomes (one from each parent), haploid organisms have just one set, making their cells 'haploid'.

In the context of reproduction, this has significant implications. In honeybees, drones arise from unfertilized eggs, which means they inherit the genetic material exclusively from the mother, with no paternal contribution. This unique reproductive strategy affects their method of producing sperm, known as spermatogenesis, which diverges from the processes observed in diploid animals.

Meiosis in Animals

Meiosis is a specialized type of cell division crucial for sexual reproduction in animals. It consists of two sequential phases: meiosis I and meiosis II. The primary goal of meiosis is to halve the chromosome number, thus producing haploid cells from an original diploid cell.

In diploid organisms, meiosis I segregates one chromosome of each pair to opposite poles, leading to the formation of two cells. Meiosis II further separates the chromatids, resulting in a total of four haploid cells. These cells develop into eggs or sperm, based on the organism's sex. However, in honeybees, since drones are haploid, their meiosis skips the chromosome number reduction step.

Sperm Production

Sperm production, or spermatogenesis, is the process by which males produce sperm cells, the male reproductive cells. In most animals, spermatogenesis includes the reduction division of meiosis, which ensures that sperm cells carry only one set of chromosomes. In turn, they can combine with the female's egg, which is also haploid, to create a diploid zygote.

However, in haploid honeybee drones, the process is simplified. Since there is only one set of chromosomes to begin with, spermatogenesis generates haploid sperm without needing to reduce chromosome numbers. This way, each sperm produced by a drone contains an identical set of chromosomes to the drone itself.

Chromosome Sets in Cells

The term 'chromosome sets' refers to the number of complete sets of chromosomes in a cell. Diploid cells, which are the norm in the animal kingdom, have two sets of chromosomes—one inherited from each parent. This is known as the '2n' condition. However, there are variations, such as haploid cells, with a single set of chromosomes labeled 'n'.

In honeybee drones, all bodily cells are haploid and carry the same single set of chromosomes due to their unique development from unfertilized eggs. When drones produce sperm, the spermatogenesis process does not have to reduce the chromosome number, since the starting cells are already haploid. This distinctive mechanism is a fascinating adaptation within the insect world.