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Chapter 2: Problem 10

Define and discuss these terms: (a) synapsis, (b) bivalents, (c) chiasmata, (d) crossing over, (e) sister chromatids, (f) tetrads, \((g)\) dyads, (h) monads.

Short Answer

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Question: Define and discuss the importance of synapsis in the process of cell division and genetics. Answer: Synapsis is the process that occurs during prophase I of meiosis, where homologous chromosomes (one from each parent) pair up closely, enabling them to exchange genetic material. During synapsis, the chromosomes form a structure called a 'bivalent' or 'tetrad'. This process plays a key role in increasing genetic diversity through crossing over and is essential for ensuring that each gamete produced during meiosis carries a unique set of genetic information.

Step by step solution

01

(a) Synapsis

Synapsis is the process that occurs during prophase I of meiosis, where homologous chromosomes (one from each parent) pair up closely, enabling them to exchange genetic material. During synapsis, the chromosomes form a structure called a 'bivalent' or 'tetrad'. This process plays a key role in increasing genetic diversity through crossing over.
02

(b) Bivalents

Bivalents, also known as tetrads, are formed during the synapsis process in meiosis. A bivalent consists of two pairs of sister chromatids, one pair from each homologous chromosome, aligned next to each other. As a result, each bivalent contains four chromatids, which allows for the exchange of genetic material during crossing over and contributes to the genetic diversity of the offspring.
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(c) Chiasmata

Chiasmata are the points where homologous chromosomes physically cross over and exchange genetic material during meiosis. Chiasmata are formed during the synapsis process when the homologous chromosomes are positioned close to each other in a bivalent or tetrad. This exchange of genetic material is referred to as crossing over.
04

(d) Crossing Over

Crossing over is the process that takes place during prophase I of meiosis when homologous chromosomes exchange genetic material at the chiasmata. This process is essential for promoting genetic diversity by recombining genetic information from both parental chromosomes and ensuring that each gamete produced during meiosis carries a unique set of genetic information.
05

(e) Sister Chromatids

Sister chromatids are pairs of identical chromosomes that are formed during DNA replication. They are joined together at the centromere, a region of DNA that holds the two chromatids together until they are separated during cell division. In meiosis, sister chromatids play a key role in genetic recombination when they are part of a bivalent or tetrad during synapsis.
06

(f) Tetrads

Tetrads, also known as bivalents, are groups of four chromatids formed during synapsis in meiosis. Each tetrad consists of two sets of sister chromatids (one from each parent) aligned closely together. This arrangement allows for the exchange of genetic material between the homologous chromosomes during crossing over, promoting genetic diversity in the offspring produced through meiosis.
07

(g) Dyads

Dyads are pairs of sister chromatids that are created during DNA replication before meiosis begins. During meiosis I, homologous dyads are aligned in tetrads to facilitate crossing over, while during meiosis II, the sister chromatids of each dyad are separated, resulting in the formation of four haploid cells called monads.
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(h) Monads

Monads are the haploid cells produced as a result of meiosis II. Each monad contains a single copy of each chromosome (in the form of a single chromatid), which represents half the genetic material of the parent cell. In sexually reproducing organisms, monads become gametes (sperm or eggs), which fuse during fertilization to form a new, genetically unique offspring.

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Most popular questions from this chapter

Contrast telophase in plant and animal mitosis.

A diploid cell contains three pairs of homologous chromosomes designated Cl and \(\mathrm{C} 2, \mathrm{M} 1\) and \(\mathrm{M} 2\), and \(\mathrm{S} 1\) and \(\mathrm{S} 2\). No crossing over occurs. What combinations of chromosomes are possible in (a) daughter cells following mitosis, (b) cells undergoing the first meiotic metaphase, (c) haploid cells following both divisions of meiosis?

Contrast spermatogenesis and oogenesis. What is the significance of the formation of polar bodies?

The nuclear DNA content of a single sperm cell in Drosophila melanogaster is approximately 0.18 picogram. What would be the expected nuclear DNA content of a primary spermatocyte in Drosophila? What would be the expected nuclear DNA content of a somatic cell (non-sex cell) in the Gl phase? What would be the expected nuclear DNA content of a somatic cell at metaphase?

What role do the following cellular components play in the storage, expression, or transmission of genetic information: chromatin, (b) nucleolus, (c) ribosome, (d) mitochondrion, centriole, (f) centromere?
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