Question

You are given a metaphase chromosome preparation (a slide) from an unknown organism that contains 12 chromosomes. Two that are clearly smaller than the rest appear identical in length and centromere placement. Describe all that you can about these chromosomes.

Short answer

Answer: From the metaphase chromosome preparation, we can gather information about the number, morphology, and classification of two small chromosomes, as well as their relationship with the other chromosomes in the organism. This analysis offers insights into the organism's overall karyotype, chromosomal organization, and genetic composition.

Step-by-step solution

(Step 1: Observing the Chromosome Number)

We have been given a slide with 12 chromosomes, including two smaller ones. From this information, we can determine the total number of chromosomes in this organism's diploid cell is 12.

(Step 2: Identifying the Small Chromosomes)

Observe the two chromosomes that are smaller than the others and have similar length and centromere placement. Given their appearance, it can be inferred that these two chromosomes are a homologous pair.

(Step 3: Analyzing Centromere Placement)

Centromere is the region where sister chromatids are connected. Depending on the placement of the centromere, chromosomes are classified into different categories such as metacentric, submetacentric, acrocentric, and telocentric. Observe the centromere placement on the smaller chromosomes to determine which category they belong to.

(Step 4: Determining Chromosome Morphology)

Analyze the overall morphology of the two smaller chromosomes. Observe the length of the arms, banding pattern, and presence of any secondary constrictions. These features can provide further insights into the structure and genetic composition of the chromosomes.

(Step 5: Comparing Smaller Chromosomes with other Chromosomes)

Compare the features of the two smaller chromosomes with the other 10 chromosomes. Observe the differences in size, centromere placement, and morphology among them. This analysis can provide more information about the organism's overall karyotype and chromosomal organization.

(Step 6: Conclusion)

By combining the observations made in the previous steps, we can gather information about the number, morphology, and classification of two small chromosomes, as well as their relationship with the other chromosomes in the given organism. Additionally, this information will provide an understanding of this unknown organism's karyotype and genetic composition.

Key concepts

Metaphase Chromosome Preparation

When studying chromosomes, scientists often analyze them during the metaphase stage of cell division. At this point, the chromosomes are easiest to observe under a microscope because they are highly condensed and aligned at the cell's equatorial plane.

The process of preparing metaphase chromosomes begins by treating cells with a compound that arrests them in metaphase, then spreading the chromosomes on a slide and staining them with dyes that bind to DNA, such as Giemsa. This staining highlights the unique banding patterns of chromosomes, helping in the identification and analysis of their structures. Metaphase chromosome preparation is critical for observing the number, size, and shape of an organism's chromosomes and for identifying potential chromosomal abnormalities.

Homologous Chromosomes

Homologous chromosomes are pairs of chromosomes that have the same length, gene sequence, and centromere placement. In a diploid organism, one chromosome of each pair comes from the mother and the other from the father.

The presence of homologous chromosomes is important for genetic variation; during meiosis, homologues can exchange sections of DNA in a process called recombination. Although they share the same genes, different alleles or versions of a gene can be found on each homologous chromosome, resulting in variation within the species.

Centromere Placement

The centromere is a specialized structure on a chromosome that is crucial during cell division as it is the attachment point for spindle fibers. The placement of the centromere also defines the shape of the chromosome.

There are four main types of centromere placement:

• Metacentric: the centromere is in the middle, resulting in arms of equal length.
• Submetacentric: the centromere is slightly off-center, creating one arm that is slightly longer than the other.
• Acrocentric: the centromere is significantly off-center but not at the very tip, leading to one very long arm and one very short arm.
• Telocentric: the centromere is at the very end, resulting in only one arm.

The position of the centromere can affect the behavior and stability of chromosomes during cell division.

Chromosome Morphology

A chromosome's morphology, or its structure and form, includes the length of its arms, the location of its centromere, and its banding pattern. Each chromosome has characteristic bands that can be observed when stained and are useful for identifying genetic landmarks and abnormalities.

The morphology of a chromosome can provide a wealth of information regarding the genetic health and characteristics of an organism. Researchers use chromosome morphology to identify numerous genetic conditions, track evolutionary relationships between species, and understand fundamental biological processes.

Genetic Composition

The genetic composition of an organism is the complete set of genes and genetic material present in each cell. Apart from the genes themselves, the genetic composition also includes non-coding sequences which play regulatory roles and other functions.

Understanding the genetic composition of an organism involves analyzing the sequence of bases in its DNA, identifying genes, regulatory elements, and chromosomal structures like telomeres and centromeres. This composition guides the organism's development, physiological processes, and it forms the hereditary blueprint passed on from one generation to the next.

Karyotype

A karyotype is an organized profile of an organism's chromosomes. It typically involves the arrangement of chromosomes by size, number, and shape. Karyotyping is used to detect chromosomal abnormalities such as extra or missing chromosomes and structural changes like translocations or inversions.

In the case of the unknown organism with 12 chromosomes, including two smaller, homologous ones, the karyotype could reveal if the organism has a typical chromosome complement for its species, or if there are variations that might influence its characteristics or health. Karyotypes are also essential for understanding species' genetics and can be especially helpful in diagnosing genetic diseases in humans.