Question

After DNA replication, a eukaryotic chromosome______ a. consists of two sister chromatids \(\mathrm{b}\) has a characteristic \(\mathrm{X}\) shape c. is constricted at the centromere d. all of the above

Short answer

The correct answer is d: all of the above.

Step-by-step solution

Identifying the Question

The question requires us to determine the correct state of a eukaryotic chromosome following DNA replication. We will evaluate each provided option to see which one correctly describes post-replication chromosomes.

Evaluating Option a

After DNA replication, each chromosome consists of two sister chromatids. These chromatids are identical copies of the chromosome, joined together at a central region called the centromere.

Evaluating Option b

In many instances, chromosomes are depicted with an X shape because each side of the X corresponds to one of the sister chromatids, and they are joined at the centromere. Hence, this representation is also accurate following DNA replication.

Evaluating Option c

Each pair of sister chromatids is joined at the centromere, a region on the chromosome that appears constricted. This description fits the structure of the chromosome following replication.

Conclusion

All the options accurately describe the state of a eukaryotic chromosome after replication. Therefore, the correct answer is option d: all of the above.

Key concepts

DNA Replication

DNA replication is a critical process that occurs in the cell cycle before a cell divides. It ensures that each new cell gets an identical copy of the DNA. During replication, the DNA molecule unwinds and separates into two strands. Each strand serves as a template for creating a new complementary strand. This process is semi-conservative, meaning that each new DNA molecule consists of one old strand and one new strand.

Key points of DNA replication include:

• The process starts at specific locations in the DNA, called origins of replication.
• Enzymes like helicase unwind the DNA, while DNA polymerase helps synthesize the new strands by adding nucleotides complementary to the templates.
• DNA replication results in two identical copies of the original DNA molecule, necessary for proper cell division.

Understanding DNA replication is essential for grasping how cells duplicate and pass genetic information accurately to daughter cells.

Sister Chromatids

Sister chromatids are the identical halves of a duplicated chromosome. They form during DNA replication when a chromosome duplicates its genetic material. These chromatids are joined together by a centromere, forming the characteristic X-shape seen during certain stages of cell division.

Some important points about sister chromatids:

• Each sister chromatid consists of a single DNA molecule, which is an exact copy of its partner.
• Sister chromatids ensure that each daughter cell receives the same genetic information during cell division.
• They stay connected at the centromere until they are pulled apart during mitosis, ensuring accurate genetic distribution.

Sister chromatids play a vital role in maintaining genetic consistency from one cell generation to the next.

Centromere

The centromere is a region on a chromosome that appears constricted. It is essential during cell division because it holds the sister chromatids together after DNA replication. Its main function is to serve as the attachment point for spindle fibers, which pull the chromatids apart during cell division.

Key features of the centromere include:

• It helps organize and align chromosomes during mitosis and meiosis.
• Special proteins bind to the centromere forming a complex called the kinetochore, vital for proper chromosome movement.
• The centromere's position can vary along the chromosome, classifying it as metacentric, submetacentric, or acrocentric based on the location.

The centromere is crucial for accurate chromosome segregation, ensuring genetic stability across generations of cells.