The main difference between a tetrad and a chromatid pair is that the tetrad contains the four sister chromatids of the bivalent, while the chromatid pair comprises the two sister chromatids of a single chromosome after DNA replication . In addition, homologous chromosomes pair during prophase I of meiosis I, while the chromatid pair emerges after DNA replication during the S phase of the interphase of the cell cycle. In addition, a tetrad can undergo homologous recombination while a chromatid pair does not undergo homologous recombination.  

Tetrad and chromatid pair are two terms used to describe different combinations of chromatids of the bivalent. In general, bivalent is a pair of homologous chromosomes that pair during meiosis. In addition, they have already undergone DNA replication.  

Key areas covered  

1. What is a tetrad - definition, formation, role 2. What is a chromatid pair - definition, formation, role 3. What are the similarities between a tetrad and a chromatid pair?   - Overview of the common characteristics 4. What is the difference between tetrad and chromatid pair - comparison of the main differences

key terms  

Chromatid pair, homologous chromosomes, homologous recombination, sister chromatids, tetrad

What is a tetrad?  

All chromosomes undergo DNA replication, thus synthesizing the exact copy of the DNA molecules that make up each chromosome. It occurs during the S phase of the interphase of the cell cycle. Here the S phase of the interphase is responsible for preparing the cell for the subsequent cell division. In addition, the homologous chromosomes pair during prophase I of meiosis I. And these two chromosomes of the homologous pair are called bivalent. Tetrad is the four sister chromatids of the two chromosomes of the homologous pair (or the divalent).

Figure 1: Chromatid pair

Here the chromatids belonging to the opposite chromosomes of the homologous pair can recombine by means of chromatid crossover. Note that the chromatids that can cross-over are the non-sister chromatids. It is important that homologous recombination is responsible for the exchange of chromosome parts, and these exchanged parts pass into different gametes. Hence, it is the main process of creating genetic variation in successive generations.  

What is a chromatid pair  

Chromatid pairs are the two chromatids of a chromosome that has undergone DNA replication. Basically, the two chromatids that are formed from the same chromosome are sister chromatids. As mentioned above, DNA replication takes place during the S phase of the interphase, which prepares the cell for subsequent cell division. The replicated chromosomes condense during metaphase I of meiosis I. And these are visible as thread-like structures under the light microscope during this step.

Figure 2: Chromatid pair

In addition, DNA replication occurs in both types of cell division; mitosis and meiosis to double the amount of DNA in the nucleus. In addition, the sister chromatids produced in this way are held together by cohesin proteins during the subsequent steps of cell division until they are separated during the anaphase of mitosis and anaphase II of meiosis II.  

Similarities Between Tetrad and Chromatid Pair  

• Tetrad and chromatid pair are two combinations of sister chromatids of homologous chromosomes.   
• Here the sister chromatids are made after DNA replication to prepare the cells for nuclear division during the growth phase of the cell cycle .   
• So both pair during the prophase of meiosis.  

Difference between a tetrad and a pair of chromatids  

definition  

Tetrad refers to the four-part structure that forms during the prophase of meiosis. It consists of two homologous chromosomes and each consists of two sister chromatids. A chromatid pair is half of two identical thread-like strands of a replicated chromosome.   

Appear  

Tetrad occurs only during prophase of meiosis I after pairing of homologous chromosomes. Meanwhile, after DNA replication, the chromatid pair occurs during the S phase of the cell cycle.  

Number of sister chromatids  

Tetrad comprises the four sister chromatids of the bivalent, while the chromatid pair comprises the two sister chromatids of a single chromosome of the bivalent.  

In the bivalent  

Tetrad comprises the sister chromatids of both chromosomes of the homologous pair, while the chromatid pair comprises only one chromosome of the homologous pair.  

origin  

Tetrad has sister chromatids of both maternal and paternal origin, while a pair of chromatids is of either maternal or paternal origin.  

Homologous recombination  

The tetrad can go through homologous recombination, while the chromatid pair does not go through homologous recombination.  

Stick together  

Chromatids of the tetrad are held together by the formation of synaptonemal complexes, while sister chromatids of the chromatid pair are held together by cohesin proteins .  

diploma  

Tetrad is the four sister chromatids of the two chromosomes of the homologous pair. In general, homologous chromosomes pair during the prophase of meiosis I. A pair of sister chromatids that belong to each of the two homologous chromosomes can also undergo homologous recombination. Meanwhile, the chromatid pair are the two sister chromatids on a particular chromosome that underwent DNA replication during the S phase of interphase. Here the cohesin proteins are responsible for holding the two sister chromatids together. Therefore, the main difference between a tetrad and a chromatid pair is the nature of the sister chromatids and their role.  

References:

1. “Meiosis I | Biology for Major Subjects I. “ Lumen , available here.

Image courtesy:

1. “0330 homologous chromosome pair.” By OpenStax ( CC BY 4.0 ) via Commons Wikimedia 2. “Figure 11 01 02” By CNX OpenStax ( CC BY 4.0 ) via Commons Wikimedia