Question

Considering Problem \(15,\) predict the number of different haploid cells that could be produced by meiosis if a fourth chromosome pair (W1 and W2) were added.

Short answer

Answer: 16 different haploid cells.

Step-by-step solution

Understanding meiosis and haploid cells

Meiosis is a type of cell division that results in four non-identical daughter cells, each having half the number of chromosomes as the parent cell. In this case, the resulting daughter cells are haploid cells, which means they contain only one set of chromosomes. Haploid cells are important for sexual reproduction where the fusion of two haploid cells (e.g., sperm and egg) results in a diploid cell with two sets of chromosomes.

Independent assortment of chromosomes during meiosis

The process of meiosis introduces genetic variations in the resulting haploid cells due to the random assortment of maternal and paternal chromosomes. This is called independent assortment, wherein chromosomes may align in any arrangement on the equatorial plane during metaphase I. So, each chromosomal pair can have two possible arrangements (one from the mother and one from the father). For multiple chromosome pairs, we can multiply the number of possible arrangements for each pair to determine the total possible combinations.

Calculate haploid cell combinations

In this problem, we have four chromosome pairs: A1/A2, B1/B2, C1/C2, W1/W2. To find the total number of different haploid cells that could be produced by meiosis, we need to calculate the possible combinations of these chromosome pairs. Since each pair has two possible arrangements (either the maternal or paternal chromosome), we can use the formula: Total number of combinations = 2^n where n is the number of chromosome pairs. In our case, n = 4. Total number of combinations = 2^4 = 16 So, considering the addition of the fourth chromosome pair (W1 and W2), 16 different haploid cells could be produced by meiosis.

Key concepts

Independent Assortment

Independent assortment is a fundamental principle of genetics first outlined by Gregor Mendel in the 19th century. During meiosis, the maternal and paternal chromosomes are shuffled in a process that is similar to shuffling a deck of cards. Each of the pairs of chromosomes segregates independently of other pairs, which contributes to the genetic diversity of sexually reproducing organisms.

Imagine lining up four different pairs of shoes, one pair for each chromosome pair. The left shoe represents the maternal chromosome and the right shoe represents the paternal chromosome. When gametes are formed through meiosis, these shoes are randomly selected to create new, unique combinations, much like how each gamete receives a mix of your parents' genes.

This randomness in the distribution of chromosomes in gametes ensures that each egg or sperm cell produced by meiosis has a different set of genetic information. So, even in our textbook exercise example, by adding another pair of chromosomes, W1 and W2, we increase the potential genetic combinations as predicted by the formula: \(2^n\), where n represents the number of chromosome pairs. Hence, with four pairs, we have \(2^4 = 16\) different combinations, creating diversity within the species.

Genetic Variation

Genetic variation is the cornerstone of evolution and the survival of species in changing environments. It's the difference in DNA among individuals which can lead to variations in traits such as eye color, height, or predisposition to certain diseases. Meiosis plays a pivotal role in creating this variation.

In addition to the mechanism of independent assortment, meiosis also involves a process called 'crossing over,' where pieces of DNA exchange between homologous chromosomes. This recombination process further shuffles the genes between the chromosomes, ensuring that each gamete - and eventually each offspring - is genetically unique.

In our example involving meiosis, aside from independent assortment, if crossing over occurs, the number of possible genetic combinations vastly increases, far surpassing the predictable 16 haploid cell variations. This randomness is essential to the resilience and adaptability of a species, especially in the face of environmental changes and stresses.

Sexual Reproduction

Sexual reproduction is the process by which two organisms produce offspring that inherit genetic material from both parents. It involves the union of haploid cells—a sperm from the father and an egg from the mother—to create a diploid cell, or zygote.

The significance of sexual reproduction lies in its ability to enhance genetic diversity within a population. This is in stark contrast to asexual reproduction, where offspring are typically genetic clones of the parent. Sexual reproduction combines the genetic material of two parents, meaning that each offspring is genetically distinct from its siblings and parents.

The role of meiosis in sexual reproduction is to ensure that each gamete carries just a single set of chromosomes. This halving of the chromosome number in gametes is crucial because it allows for the restoration of the full chromosome complement when two gametes fuse during fertilization, maintaining the species-specific chromosome number across generations. As indicated in our textbook exercise problem, the 16 different haploid cells produced by meiosis due to the addition of a fourth chromosome pair contribute to the vast genetic diversity observed in sexually reproducing organisms.