Cell & Nuclear Division

Define Mitosis

The process which by a nucleus divides to produce 2 daughter nuclei containing identical sets of CHs to the parent nucleus

Define Meiosis

The process which by a nucleus divides into 4 daughter nuclei containing half the no. of CHs of the parent nucleus

Define Mitosis

The process which by a nucleus divides to produce 2 daughter nuclei containing identical sets of CHs to the parent nucleus

Define Meiosis

The process which by a nucleus divides into 4 daughter nuclei containing half the no. of CHs of the parent nucleus

Outline the relationship between DNA, CHt and CHs

1. DNA is coiled around proteins to form nucleosomes

2. When groups of nucleosome are intensely coiled upon themselves, they form a CHt thread

3. During prophase, Cht is further condensed into a CHs

Define Kineotchore

A disc-shaped protein complex of a CHs that allows spindle fibres to attach during cell division

Define Centromere

The region of a CHs that holds 2 sister chromatids together

Define Duplicated CHs

CHs that has gone through DNA replication and appears as 2 identical sister chromatids bound at the centromere

Define Homologous CHs

A pair of CHs that have the same gene loci, length and shape which determines the characteristics in an organism

State the 6 properties of Homologous CHs

1. Same length

2. Same centromere position

3. Genes coding for the same characteristics at similar loci

4. Pair with each other using Prophase 1 of meiosis

5. CHs comes from 2 parents

6. Does not need to be completely identical

State what happens during Prophase

1. CHt condenses (CHs becomes visible)

2. Each CHs consists of 2 sister chromatids joined at the centromere

3. Centrioles migrate to opposite poles of the cell [Animal Cells]

4. The nucleolus and nuclear envelope break down

State what happens during Metaphase

1. CHs arrange themselves 90° to spindle axis at the equator of the cell

2. CHs are attached to the spindle fibres at the centromere

State what happens during Anaphase

1. Centromere of each CHs divides, causing the sister chromatids to separate

2. Spindle fibres shorten, causing the sister chromatids to move to opposite poles of the cell

State what happens during Telophase

1. Sister chromatids reach their respective poles of the cell (becomes the CHs of the daughter cells)

2. CHs uncoil and becomes CHt

3. Spindle fibres break down

4. Nucleolus and nuclear envelope reform around the CHt

State what happens during Prophase I

1. CHt condenses (CHs becomes visible)

2. HCHs pair up (synapsis), forming bivalents

4. Chiasmata may form between non-sister chromatids of a bivalent (crossing-over)

3. Centrioles migrate to opposite poles of the cell [Animal Cells]

4. The nucleolus and nuclear envelope break down

State what happens during Metaphase I

1. Bivalents arrange themselves 90° to spindle axis at the equator of the cell, forming 2 rows

The arrangement of bivalents is completely random

2. CHs are attached to the spindle fibres at the centromere

State what happens during Anaphase I

1. Bivalents separate

2. Spindle fibres shorten, causing the CHs to move to opposite poles of the cell

State what happens during Telophase I

1. CHs reach their respective poles of the cell (becomes the CHs of the daughter cells)

3. Spindle fibres break down

4. Nucleolus and nuclear envelope reform around the CHs

State what happens during Prophase II

1. CHt condenses (CHs becomes visible)

2. Each CHs consists of 2 sister chromatids joined at the centromere

3. Centrioles migrate to opposite poles of the cell [Animal Cells]

4. The nucleolus and nuclear envelope break down

5. Spindle fibres develop perpendicular to spindle axis of Meiosis I

State what happens during Metaphase II

1. CHs arrange themselves 90° to new spindle axis at the equator of the cell

2. CHs are attached to the spindle fibres at the centromere

State what happens during Anaphase II

1. Centromere of each CHs divides, causing the sister chromatids to separate

2. Spindle fibres shorten, causing the sister chromatids to move to opposite poles of the cell

State what happens during Telophase II

1. Sister chromatids reach their respective poles of the cell (becomes the CHs of the daughter cells)

2. CHs uncoil and becomes CHt

3. Spindle fibres break down

4. Nucleolus and nuclear envelope reform around the CHt

State the 4 functions of Mitosis

1. Maintains genetic stability of a cell or an organism from one generation to the next

2. Growth and development

3. Replacement of worn-out parts

4. Basis of asexual reproduction

State the 2 functions of Meiosis

1. Production of haploid gametes for sexual reproduction

2. Creates genetic variation crucial for evolution