The correct answer is A. Tetrad.
A tetrad is a group of four chromatids that are held together by a centromere. They are formed during meiosis I, when homologous chromosomes pair up and exchange genetic material.
A gamete is a reproductive cell that is produced by meiosis. It contains half the number of chromosomes as a somatic cell.
A chromatid is one of the two identical strands that make up a chromosome. They are joined together at the centromere.
A zygote is a fertilized egg cell. It contains the full complement of chromosomes, one from each parent.
Here is a diagram of a tetrad:
As you can see, the tetrad consists of two pairs of homologous chromosomes. Each homologous chromosome is made up of two chromatids. The chromatids are held together at the centromere.
During meiosis I, the homologous chromosomes pair up and exchange genetic material. This process is called crossing over. After crossing over, the homologous chromosomes separate and each daughter cell receives one of each homologous chromosome.
The following table summarizes the differences between the four options:
| Option | Description |
|—|—|
| Tetrad | A group of four chromatids that are held together by a centromere. They are formed during meiosis I, when homologous chromosomes pair up and exchange genetic material. |
| Gamete | A reproductive cell that is produced by meiosis. It contains half the number of chromosomes as a somatic cell. |
| Chromatid | One of the two identical strands that make up a chromosome. They are joined together at the centromere. |
| Zygote | A fertilized egg cell. It contains the full complement of chromosomes, one from each parent. |