What is a chromatid?

What is a chromatid?

• A. A tetrad
• B. One of two identical sister parts of a duplicated chromosome
• C. The exchange of genetic material between chromatids
• D. A replicated chromosome

Answer: (B)

A chromatid is one of two identical copies that make up a duplicated chromosome. After DNA replication, each chromosome consists of two sister chromatids held together at the centromere; each chromatid is an exact copy of the other. That’s why this option is best: it defines a chromatid as one half of the duplicated chromosome, while the whole replicated chromosome would refer to both chromatids together, not just one. The other ideas don’t fit: a tetrad is four chromatids (two homologous chromosomes) paired during meiosis; crossing over is the exchange of genetic material between chromatids; a replicated chromosome describes the full structure of two chromatids together, not the single chromatid itself.

A chromatid is one of two identical copies that make up a duplicated chromosome. After DNA replication, each chromosome consists of two sister chromatids held together at the centromere; each chromatid is an exact copy of the other. That’s why this option is best: it defines a chromatid as one half of the duplicated chromosome, while the whole replicated chromosome would refer to both chromatids together, not just one.

The other ideas don’t fit: a tetrad is four chromatids (two homologous chromosomes) paired during meiosis; crossing over is the exchange of genetic material between chromatids; a replicated chromosome describes the full structure of two chromatids together, not the single chromatid itself.