Genetics Chapter 3: The Cell Cycle

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Questions and Answers

What is the primary function of the G2 phase in the cell cycle?

Chromosome duplication

Gene expression and RNA transcription

Cell growth and preparation for mitosis (correct)

DNA synthesis

Which phase of the cell cycle lasts the shortest duration?

G2 phase

M phase (mitosis) (correct)

G1 phase

S phase

What happens during prophase?

Chromatin condenses into chromosomes (correct)

The cell remains in a resting state

Nuclear division occurs

Chromatids separate to opposite poles

What is the significance of the centromere in chromatids?

It is the site where sister chromatids are held together Signup and view all the answers

Which proteins are specifically involved in regulating the transitions between the phases of the cell cycle?

Cyclins Signup and view all the answers

How long does it typically take for most eukaryotic cells to complete a full cell cycle?

18 to 24 hours Signup and view all the answers

During which cell cycle phase does the entire genome get duplicated?

S phase Signup and view all the answers

What characterizes cells in the G0 phase?

They no longer divide and are in a resting state Signup and view all the answers

What happens to chromosomes during cell division?

Chromosomes coil and condense. Signup and view all the answers

What are telomeres?

The natural ends of a chromosome. Signup and view all the answers

How is DNA organized into chromosomes in eukaryotic cells?

DNA is associated with proteins in structures called chromatin. Signup and view all the answers

Which term describes the area where two chromatids are joined?

Centromere Signup and view all the answers

What identifies the shorter arm of a chromosome?

p arm Signup and view all the answers

What is the second level of organization of DNA in the nucleus?

30 nm fiber Signup and view all the answers

What structure is formed by the first level of DNA organization?

Nucleosome Signup and view all the answers

Which characteristic is NOT true about chromatin?

Chromatin exists only as linear structures. Signup and view all the answers

What is the primary function of kinetochores during cell division?

To connect microtubules to chromatids Signup and view all the answers

What occurs during anaphase?

Chromatids separate and migrate to opposite poles Signup and view all the answers

How does meiosis differ from mitosis?

Meiosis produces haploid cells through two nuclear divisions Signup and view all the answers

What happens to the nuclear envelope during the later stages of mitosis?

It reforms along with nucleoli Signup and view all the answers

What is the significance of the division furrow during cytokinesis?

It separates the two daughter cells Signup and view all the answers

What is genetic recombination, and when does it occur in meiosis?

The exchange of genetic material between homologous chromosomes in Meiosis I Signup and view all the answers

During which phase of mitosis do the microtubules disappear?

Telophase Signup and view all the answers

What is the role of centrioles during cell division?

To migrate to opposite poles and aid in the formation of spindle fibers Signup and view all the answers

What is the role of the histone protein H1 in the formation of chromatin?

It aids in the formation of a solenoid structure. Signup and view all the answers

What type of chromatin is described as highly condensed?

Heterochromatin Signup and view all the answers

What structure is formed by the pairing of homologous chromosomes during Prophase I?

Tetrads Signup and view all the answers

What is the significance of DNA compaction during cell division?

It prevents entanglement of chromosomes. Signup and view all the answers

During which stage of Prophase I is synapsis completed?

Pachytene Signup and view all the answers

What is the maximum supercoiling that a DNA molecule can undergo called?

Chromatid Signup and view all the answers

What occurs during mitosis concerning chromosome numbers?

It maintains the chromosome number. Signup and view all the answers

What begins to separate in the Diplotene stage of Prophase I?

Homologous chromosomes Signup and view all the answers

In eukaryotic organisms, how many sets of chromosomes are present in somatic cells?

2 sets (2n) Signup and view all the answers

What occurs at Metaphase I of meiosis?

Chromosomes move to the cell's equator Signup and view all the answers

Which process results in the division of chromosome number by half?

Meiosis Signup and view all the answers

What happens to the number of chromosomes during the first division of meiosis?

It is reduced from 2n to n Signup and view all the answers

Which structure organizes chromatin into loops and helices?

Scaffold Signup and view all the answers

Which stage of meiosis II is directly analogous to mitosis?

Anaphase II Signup and view all the answers

What structure disappears during Telophase I of meiosis?

Microtubules Signup and view all the answers

Which stage of Prophase I finds the chromatin transitioning to chromosome form?

Leptotene Signup and view all the answers

What is the primary result of meiosis in terms of chromosome number?

It produces 4 haploid cells. Signup and view all the answers

Which process describes the alignment of chromosomes at the equatorial plate during cell division?

Metaphase Signup and view all the answers

In which stage of meiosis do chromatids separate and migrate towards opposite poles?

Meiotic Anaphase II Signup and view all the answers

What is the genetic makeup of gametes produced through meiosis?

Genetically different from one another Signup and view all the answers

If a somatic cell contains 20 chromosomes, how many chromosomes will each gamete contain?

10 chromosomes Signup and view all the answers

Which of the following types of cells are diploid?

Somatic cells Signup and view all the answers

In the meiosis of gametes, which of the following statements is true regarding chromatids?

Each gamete carries one chromatid per chromosome. Signup and view all the answers

What is the chromosome configuration in a cell after Meiotic Anaphase I?

Homologous chromosomes are separated. Signup and view all the answers

Which of these describes the composition of autosomal chromosomes in male or female gametes if n=10?

9 autosomal and 1 sex chromosome Signup and view all the answers

What happens to the nuclear envelope during telephase?

It reforms around the chromosomes. Signup and view all the answers

Study Notes

Ferhat Abbas University, Setif 1

Faculty of Natural and Life Sciences
Department of Basic Studies
2nd Year LMD
Module: Genetics
Academic Year 2024/2025
Module Coordinators: Dr Bouzid and Dr Ouaret-Guidoum Mona ([email protected])
Dates: 27/10 - 07/11/2024

Chapter 3: The Cell Cycle in Eukaryotes

Transmission of Genetic Traits During Mitosis and Meiosis
Key concepts included Interphase and Mitosis

Concepts of Chromatin and Chromosome

During cell division (mitosis or meiosis), chromatin coils and condenses into chromosomes, visible under a microscope.
Outside of cell division, chromosomes unwind and decondense to form chromatin, dispersed in the nucleus.

Chromosome Morphology

Each chromosome consists of two chromatids joined at a condensed region called the centromere.
Chromosome arms extend from either side of the centromere.
The shorter arm is called the "p arm," and the longer arm is called the "q arm."
Telomeres are the natural ends of the chromosome.

Types of Chromosomes Based on Centromere Location

During cell division, chromosomes appear in various sizes and shapes.
Based on the centromere location, chromosomes are classified into metacentric, submetacentric, acrocentric, and telocentric.

Organization of DNA into Chromosomes

DNA in eukaryotic cells is always associated with proteins, forming a structure called chromatin.
There are different levels of DNA compaction.
The first level is the nucleosome, a bead-like structure formed by DNA wrapped around histone proteins(2 H2A, 2 H2B, 2 H3, and 2 H4).

Second Level of Organization: Chromatin

A 30 nm fiber, corresponding to the natural state of DNA in the nucleus.
Nucleosomes wrap around themselves to form a solenoid, with the help of a histone protein H1.
Highly condensed chromatin is called heterochromatin; less condensed is called euchromatin.

Third Level of Organization: The Chromatid

The maximum supercoiling of DNA, occurring when the 30 nm chromatin fiber condenses to form a chromatid.
Chromatin is organized into loops and helices around a central protein structure.

The Cell Cycle in Eukaryotes

Unicellular and multicellular eukaryotes possess organelles and a cytoskeleton.
DNA is compacted into chromosomes during cell division.
Eukaryotes exhibit true sexuality.

Eukaryotic Cell Division Processes

Multicellular organisms develop from a single fertilized egg.
Chromosomes are present in a diploid number (2n) in somatic cells and a haploid number (n) in sexual cells.
This indicates two nuclear division processes: Mitosis and Meiosis.
Mitosis maintains the number of chromosomes and meiosis divides their number by half.

The Cell Cycle

Eukaryotic cells go through repeating stages in the cell cycle.
Each cell cycle includes:
- A DNA synthesis phase (S phase, ~8 hrs). followed by.
- A gap phase (G2 phase, ~4 hrs).
- Mitosis (M phase, ~1 hr), followed by.
- A gap phase (G1 phase, various duration).

Control of the Cell Cycle

Every cell must maintain a memory of its phase in the cell cycle (G1 or G2).
Cell cycle transitions (G1→S, G2→M) are controlled by specific cell cycle proteins.
These proteins are encoded by numerous genes called cdc (cell division cycle).
The G0 phase is a non-dividing state, which is a part of the interphase.

Interphase

Interphase is the time between cell divisions.
It is characterized by an increase in cell volume to accommodate more organelles for offspring.
RNA transcription and enzyme secretion occur during the G1 phase. -DNA replication and chromosome duplication occur during the S phase.
Further growth and preparation for mitosis occur during the G2 phase.

Mitosis (and Meiosis) Stages

In eukaryotes most cells take 18-24 hours to complete a full cycle.
The duration of each phase varies among cells, with mitosis always being the shortest.
- Prophase
- Metaphase
- Anaphase
- Telophase (and cytokinesis).

Prophase(and Meiosis stages)

Condensation of chromatin into chromosomes.
Breakdown and fragmentation of the nuclear membrane.
Migration of centrioles to opposite ends of the cell
Formation of the spindle fibers.

Prometaphase

Fragmented nuclear envelope
Connection of kinetochores to microtubules.
Chromosome movement resulting from tension

Metaphase

Chromosomes align at the cell's equator (metaphase plate).
Chromosomes are aligned according to their centromeres.

Anaphase

Sister chromatids are "pulled apart" to opposite poles.
The centrioles will migrate along their respective poles.

Telophase

Chromosomes decondense into chromatin.
New nuclear membranes are formed around the separated sets of chromosomes.
The microtubules disappear.
Cytokinesis occurs, separating the cytoplasm and organelles.

Meiosis

Meiosis is a reductive cell division that produces gametes (sex cells) for sexual reproduction.
Meiosis produces haploid cells from diploid cells (2n → n).
Meiosis allows for genetic recombination to generate genetically distinct gametes.
Meiosis involves two successive divisions (Meiosis I and Meiosis II).

Meiosis I Stages

Prophase I: Homologous chromosomes pair up and align along their entire length, forming tetrads. -Zygotene, Pachytene, Diplotene, and Diakinesis are distinct stages of this phase.
Metaphase I: Homologous chromosome pairs align along the metaphase plate.
Anaphase I: Homologous chromosomes separate and move to opposite poles.
Telophase I: Chromosomes arrive at opposite poles, and cytokinesis follows.

Meiosis II Stages

Prophase II: Chromosomes condense, and the nuclear envelope breaks down if not already broken.
Metaphase II: Individual chromosomes align along the metaphase plate.
Anaphase II: Sister chromatids separate and move to opposite poles.
Telophase II: Chromosomes decondense; nuclear envelope reforms, resulting in 4 genetically different haploid cells.

Relationship between chromatids and chromosomes

Depending on the stage of division and the type of division, we can have different combinations of chromosomes and chromatids.

Two Types of Cells

Somatic cells and germ cells (2n), and sex cells (gametes n).
Examples provided comparing autosomal and sex chromosomes to show 2n and n.

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Description

Test your knowledge on the cell cycle in eukaryotes, specifically focusing on the transmission of genetic traits during mitosis and meiosis. This quiz covers key concepts such as interphase, chromosome morphology, and the roles of chromatin and chromosomes during cell division.