Problem 3 - Biology Today and Tomorrow with Physiology

Question

How many chromatids does a duplicated chromosome have? a. one b. two c. three d. four

Step-by-Step Solution

Answer

A duplicated chromosome has two chromatids.

Step 1: Understanding Chromosomes

Chromosomes are structures within cells that contain DNA. A single non-duplicated chromosome consists of one DNA molecule, tightly coiled around proteins.

Step 2: Definition of Chromatid

A chromatid is one half of a duplicated chromosome. After DNA replication, a chromosome consists of two identical copies called sister chromatids.

Step 3: Counting Chromatids in Duplicated Chromosomes

When a chromosome is replicated, it forms two sister chromatids. These chromatids are identical and are joined at a region called the centromere.

Step 4: Conclusion on the Number of Chromatids

Given that each duplicated chromosome has two sister chromatids, the answer is option b. two.

Key Concepts

Chromatid

A chromatid is a crucial part of the chromosome structure. When you look at a duplicated chromosome, you see two strands. Each of these strands is known as a chromatid. A chromatid contains a single, tightly-coiled DNA molecule. They form as a result of DNA replication and are necessary for cell division. Each chromatid is identical to its partner, and this feature plays a vital role during the process of cell division. In simpler terms, think of chromatids as the two "arms" of a duplicated chromosome that ensure genetic information is passed accurately to the next generation of cells.

Sister Chromatids

When a chromosome duplicates, what you get are two sister chromatids. These are essentially two identical copies of a chromosome, containing the same genetic material. This identical nature is significant because it ensures that when cells divide, each new cell gets a perfect copy of the DNA.
Sister chromatids are connected to each other at a central point called the centromere. During cell division, specifically in mitosis and meiosis, sister chromatids are pulled apart. This process ensures each daughter cell ends up with the right amount of genetic material.

• Identical copies: Ensure consistency of genetic material.
• Joined at the centromere: Mark the paired nature until cell division.
• Separated during cell division: Distribute genetic material evenly.

DNA Replication

DNA replication is a pivotal biological process that occurs before cell division. It essentially involves copying the DNA molecule in a cell. This ensures that both daughter cells have the same genetic information as the parent cell.
During replication, the DNA double helix unwinds, and each strand serves as a template for creating a new complementary strand. This results in the formation of two identical DNA molecules, which means that each chromosome now consists of two sister chromatids. This process is critical as it guarantees genetic fidelity across generations of cells.

• Unwinding: The DNA double helix unzips to allow replication.
• Template strands: Each original DNA strand serves as a guide.
• Result: Two identical DNA molecules form, creating sister chromatids.

Centromere

The centromere is a specialized region of the chromosome that plays a critical role in cell division. This is where the sister chromatids are held together, allowing them to stay paired until they are ready to be separated during cell division. The centromere ensures that each chromatid pair is recognized and manipulated correctly during the transfer process.

• Attachment site: Holds the sister chromatids together.
• Essential for distribution: Plays a key role during chromosome segregation.
• Spindle attachment: During cell division, the centromere attaches to spindle fibers, facilitating chromatid movement.

Understanding the centromere's role helps explain how the cell ensures accurate genetic information distribution.