Chromosome, Chromatids

CELL
DIVISION

DB014 2023/2024 CHAPTER 3

​You are required to read the lesson slides before attempting each question.

​Important Terminologies

​ Sister chromatids: the identical copies (chromatids) formed by the DNA replication of a chromosome

​ Homologous chromosomes:Two chromosomes in a pair – normally one inherited from the mother and one from the father.

The chromosomes in a homologous pair each have the same genes in the same order, but there may be variation between them, resulting in different alleles.

​/tetrad

​ Bivalent/ tetrad:  Each pair of homologous chromosomes consists of four chromatids which are undergoing synapsis. 

​Chiasma: a point at which paired chromosomes undergo crossing over and exchange of genetic material occur between the strands.

Synapsis
The pairing and physical connection of one duplicated chromosome to its homolog during Prophase I

Crossing Over:
the exchange of genetic
material between non-sister
chromatids of homologous
chromosomes during meiosis

Multiple Choice

How many tetrads and chiasma are shown in the figure?

• Tetrads: 3

  Chiasma: 6

• Tetrads: 6

  Chiasma: 6

• Tetrads: 6

  Chiasma: 3

• Tetrad: 6

  Chiasma: 12

*Hint: To determine the number of chromosomes, count the number of centromeres

Chromosomal number

The number of complete sets of chromosomes in a cell.

Ploidy Level & Chromosomal Number

Ploidy

n=3

2n=6

Multiple Choice

State the ploidy level and the number of chromosomes shown in the figure.

• n=8

• 2n=8

• n=16

• 2n=16

DB014 CHAPTER 3 (3 HOURS)

Mitosis

▪Each cell produces2
daughter cells.

Each daughter cell contain :

Same number

(2n)

of

chromosome as

the parent.

Meiosis

▪Each cell produces4
daughter cells.

Each daughter cell contain :

half (n)
as many

chromosome as
the parent cell.

​2n=4

​2n=4

​2n=4

​2n=4

​n=2

​n=2

​n=2

​n=2

Multiple Choice

If a diploid cell contains 10 chromosomes, choose the correct ploidy level and the number of chromosomes in the cell after;

• Mitosis: 2n=20

  Meiosis: n=10

• Mitosis: 2n=10

  Meiosis: n=5

• Mitosis: n=20

  Meiosis: 2n=10

• Mitosis: n=10

  Meiosis: 2n=5

Prophase

Metaphase

Anaphase

Telophase

MITOSIS
Definition

A process by whicha cell nucleus divides

to producetwodaughter cells; each contain theidentical number of chromosomes to
the parent cellfollowed by cytokinesis

DB014 CHAPTER 3 (3 HOURS)

09

https://images.app.goo.gl/d2YSriN83sYadm2J6

Multiple Choice

Arrange the phases of mitosis according to the correct sequence.

• I-II-III-IV

• II-IV-III-I

• I-IV-II-III

• IV-II-III-I

General Rules​
Mitosis vs Meiosis I: different chromosomal behaviour but same number of chromosomes.

Mitosis vs Meiosis II: similar chromosomal behaviour but different number of chromosomes (chromosome number is half/n in meiosis II)

Meiosis I vs Meiosis II:
different chromosomal behaviour and number of chromosomes

(chromosome number is half/n in meiosis II)

​Prophase vs Prophase I vs Prophase II

Similarities

• Chromatin / chromosome shortens, thicken and condense

• Nuclear membrane & nucleolus disintegrate / disappear

• A pair of sister chromatids attached together at centromere

• Centrosome migrate to opposite poles / spindle fiber begins to form

• No synapsis (Homologous chromomes do not pair up.)

• No crossing over

• Chromosome number is diploid.

• Synapsis (Homologous chromomes do not pair up)

• Crossing over occurs at chiasmata.

• Chromosome number is diploid

• No synapsis (Homologous chromomes do not pair up.)

• No crossing over

• Chromosome number is haploid

​2n=4

​2n=4

​n=2

​Differences

Multiple Choice

State the phase and the chromosomal event shown in the figure.

• Prophase: no synapsis and crossing over between non-sister chromatids

• Prophase I: synapsis and crossing over occurs between non-sister chromatids

• Prophase II: no synapsis and crossing over between non-sister chromatids

• Prophase II: synapsis and crossing over occurs between non-sister chromatids

Multiple Choice

State the phase and the chromosomal number shown in the figure.

• Prophase, n=6

• Prophase, 2n=6

• Prophase I, n=6

• Prophase I, 2n=6

• Prophase II, n=6

​Metaphase vs Metaphase I vs Metaphase II

• Chromosomes align at metaphase plate

• Homologous chromosomes align at metaphase plate (Chromosomes line up in pairs)

• Chromosomes align at metaphase plate (same chromosomal behaviour as Metaphase but chromosomal number is halved)

​2n=4

​2n=4

Metaphase

Metaphase I

Metaphase II

​n=2

Multiple Choice

A diploid cell has 6 chromosomes. Determine the phase and chromosomal behaviour of the cell as shown in the figure.

• Metaphase: chromosomes align at metaphase plate

• Metaphase I: Homologous chromosomes align at metaphase plate

• Metaphase II: Chromosomes align at metaphase plate

• Metaphase II: Homologous chromosomes align at metaphase plate

​Anaphase vs Anaphase I vs Anaphase II

• Sister chromatids separate and move to the opposite poles

• Centromeres split

• Homologous chromosome separate and move to the opposite poles

• Centromeres do not split

• Sister chromatids separate and move to the opposite poles

• Centromeres split

  (same chromosomal behaviour as Anaphase but chromosomal number is halved)

Anaphase

Anaphase I

Anaphase II

Multiple Choice

State the phase and the chromosomal behaviour shown in the figure.

• Anaphase: Sister chromatids separate & move to the opposite poles

• Anaphase: Homologous chromosomes separate & move to the opposite poles

• Anaphase I: Sister chromatids separate & move to the opposite poles

• Anaphase I: Homologous chromosomes separate & move to the opposite poles

• Anaphase II: Sister chromatids separate & move to the opposite pol

​Telophase vs Telophase I vs Telophase II

• Chromosomes arrive at the opposite poles (each chromosomes consist of 1 chromatids)

• Each pair of homologous chromosomes arrive at the opposite poles.

• Chromosomes arrive at the opposite poles (each chromosomes consist of 1 chromatids)

  *same chromosomal behaviour as Telophase but chromosomal number is halved

Telophase

Telophase I

Telophase II

Similarities

• Nuclear membrane & nucleolus reappear

• Spindle fibre disintegrates.

Multiple Choice

Name the phase shown in the figure. What is the ploidy level and chromosomal number in each cell at the end of this phase?

• Telophase. n=3

• Telophase. 2n=6

• Telophase I. n=3

• Telophase I. 2n=6

• Telophase II. n=3

CYTOKINESIS

Division of the cytoplasm

DB014 CHAPTER 3 (3 HOURS) 15

(b) Describe briefly the cytokinesis process in animal and plant

Multiple Choice

Which of the following is true about cytokinesis in animal and plant cells?

• Cytokinesis in animal cells involves formation of cleavage furrow while cytokinesis in plant cells involves formation of cell plate.

• Cytokinesis in animal cells begins inner outwards while cytokinesis in plant cells involves outter inwards.

• In animal cells, vesicles containing hemicellulose and pectin are formed while in plant cells, contractile ring made of microtubule is formed