Question

Drag the terms on the left to the appropriate blanks on the right to complete the sentences. Tetrads) Crossing over) (Synapsis) Dyads Bivalents Sister chromatids Monad Chiasmata ) 1._____is the point-by-point pairing of homologous chromosomes during prophase of meiosis I. 2. _____are those structures formed by the synapsis of homologous chromosomes. 3. _____refers to the structure, when viewed microscopically, of crossed chromatids. 4. _______is the exchange of genetic material between chromatids. 5. _____are the post-S phase structure of replicated chromosomes. 6. ______are synapsed homologous chromosomes thereby composed of four chromatids. 7. ______are composed of two chromatids joined by a centromere. 8. A sister chromatid is also called a _____.

Answer 1

1. Synapsis

2. Bivalents

3. Chiasmata

4. Crossing over

5. Dyads

6. tetrads

7. Chromosomes

8. Monad

Step-by-step explanation:

The cell cycle is mainly divided into 2 stages namely;

1. The interphase
2. The m or division phase

The interphase is further divided into the
`G_0, G_1, S` and
`G_2` phase representing resting, cell development, DNA synthesis and protein synthesis stage respectively while the m phase represents mitotic or meiotic cell division depending on the cell.

Chromosomes are contained in the DNA and are therefore synthesized or replicated along in the S-phase. Typical post-S phase chromosomes are usually made up of 2 sister chromatids and are sometimes referred to as dyads. A sister chromatid is also often referred to as monad.

Meiosis involves the division of sex cells and it is usually a 2-staged division - meiosis I and meiosis II. While meiosis II is entirely a mitotic division, the bulk of the distinguishing processes of meiosis happens in meiosis I - prophase I to be precise.

The prophase I of meiosis I is further divided into leptotene, zygotene, pachytene and diplotene stage based on the behaviour of chromosomes.

The leptotene stage is essentially a stage where chromosomes compact and become visible as thin threads. During the zygotene stage, homologous chromosomes start pairing up in a process known as synapsis which results in the formation of a complex structure known as synaptonemal complex.

Since each chromosome in a normal cell is made up of 2 sister chromatids joined together at the centromere. Hence, two synapsed chromosomes form a 4-chromatids structure known as bivalents or tetrads.

Paired chromosmes then go ahead to exchange genetic materials between non-sister chromatids in a process known as crossing over at the pachetene stage. The diplotene stage is marked by dissolution of the synaptonemal complex, although homologous chromosomes are still held together at the site of crossing over. The site is usually seen under the microscope as a X-shaped structure, otherwise known as the chiasmata.