Cell Division Flashcards
What is mitosis?
A type of nuclear division that results in the production of two daughter nuclei that are genetically identical to the parent cells This means that the daughter nuclei have the same number of chromosomes as the parent nucleus
What are the three stages in cell cycle
Interphase, mitosis, and cell division ( cytokinesis )
What happens during interphase?
The cells absorb nutrients, synthesize new organelles, build up protoplasm and replicates DNA
Before the cell enters the nuclear division phase, the chromatin threads replicate, the centrioles replicate and divide
What happens during DNA replication?
The chromatin threads replicates to produce two identical chromatin threads that coil and shorten to become chromosomes. Chromosomes are only visible during cell division as short, thick, x-shaped structures. Each chromosome contains two identical DNA molecules known as sister chromatids. The sister chromatids are joined at a point known as the centromere
What are the 4 stages of mitosis?
Prophase
Metaphase
Anaphase
A\telophase
What happens during prophase?
Chromatin threads condense, coil and shorten to become chromosomes that each consists of 2 sister chromatids attached at the centromere.
They now become visible under a microscope as x-shaped structures
In an animal cell, asters form around the centrioles.
The 2 pairs of centrioles move apart to opposite ends/poles of the cells.
The nucleolus and nuclear envelop disappears and a spindle forms with spindle fibres extending from one pole of the cell to the other
What happens during metaphase?
Chromosomes line up along the equatorial plane of the spindle.
The centromere of each chromosome is attached on both sides to a spindle fibre
What happens during anaphase?
Each centromere divides.
The spindle fibres shorten and pull the chromatids apart to opposite poles of the cell
Once the chromatids are separated, they are known as daughter chromasomes
What happens during telophase?
Spindle fibres break down
A nuclear envelope forms around the chromosomes at each pole of the cell
A nucleolus reforms in each nucleus and the chromosomes uncoil and lengthen to become thin chromatin threads
What happens during cytokinesis?
The cytoplasm divides.
In animal cells, cleavage / furrows appear in the cytoplasm between the two nuclei
The furrows deepen and 2 identical daughter cells are finally produced
What is the difference between mitosis in plant and animal cells?
Animal: centrioles are present
Plant: centrioles are absent
Animal: cleavage of cytoplasm occurs during cytokinesis
Plant: cleavage of cytoplasm does not occur during cytokinesis
Animal: cell plate does not form between 2 daughter nuclei and instead cleavage of cytoplasm occurs
Plant: cell plate is formed between 2 daughter nuclei, dividing the cell into 2. The cell plate is formed by the fusion of a small fluid-filled vesicles produced by the Golgi apparatus
Why is mitosis important?
It enables the growth of an organism
Mitosis is needed for the repair of worn-out parts of the body
Mitosis allows asexual reproduction to occur
What are gametes?
Reproductive cells that contains half the number of chromosomes as the normal body cells
What is meiosis?
A form of nuclear division that produced daughter nuclei containing half the number of chromosomes as the parent nucleus
How do gametes differ from normal body cells?
Gametes have half the number of chromosomes as compared to normal body cells
What happens during prophase 1?
Chromatin threads condense,coil and shorten to become chromosomes
Homologous chromosomes pair along their whole length. This is called a synapsis.
The homologous chromosomes cross over; the point where they cross over is called a chiasma
The strength of their coiling may cause them to break and exchange parts in a process called crossing over
Crossing over results in new combinations of alleles across the chromosomes
The chromosomes shorten further
Asters form around the centrioles which moves apart to opposite poles of the cells
The nuclear envelope and nucleolus disappear
Spindle fibres form
What happens during metaphase 1?
The pairs of homologous chromosomes arrange themselves along the equatorial plane of the spindle
Each chromosome is attached to a spindle fibre
What happens during anaphase 1?
The homologous chromosomes separate and
are pulled to opposite poles of the cell
As the spindle fibres shorten
What happens during telophase 1?
A nuclear envelope forms around the chromosomes at each pole
What happens during cytokinesis 1?
The cytoplasm cleaves into 2, producing 2 daughter cells
Each with the haploid number of chromosomes
The centrioles divide
What happens during prophase 2?
The 2 pairs of centrioles move to opposite poles of the cell
The nuclear envelope disappears
Spindle fibres appear
What happens during metaphase 2?
Chromosomes arrange themselves singly along the equatorial plane of the spindle
What happens during anaphase 2?
The centromeres divide
Sister chromatids separate to become daughter chromosomes
Which are pulled towards opposite ends of the cell
What happens during telophase 2?
Spindle fibres disappear
Nuclear envelope forms around 2 daughter chromosomes at each pole
A nucleolus reforms
What happens during cytokinesis 2 ?
Cleavage of cytoplasm results in 4 daughter cells being produced, each with half the number of chromosomes as the parent cell
Why is meiosis important?
Meiosis produces haploid gametes
Haploid gametes fuse with another haploid gamete to form a diploid number gamete to maintain the normal diploid number of chromosomes in the species
Meiosis results in variations in the gametes produced
Variations occur due to crossing over and independent assortment of chromosomes
What is independent assortment?
The process whereby one chromosome from each pair can combine with either chromosome of the pair resulting in 4 different gametes being produced from 2 chromosomes.
Since fertilisation is random , such variations in the gametes produce variations in the offspring
Why is variation important?
Variations increase the chances of survival of the species during changes in the environment. When environmental conditions change, nature will ‘select’ those organisms with favourable characteristics to survive, while others die. Those that survive will pass on their favourable genes to their offspring, ensuring the continuity of the species
What are the differences in meiosis and mitosis?
Mitosis: daughter cells contain the same number of chromosomes as the parent cell
Meiosis: daughter cells contain half the number of chromosomes as the parent cell
Mitosis: pairing of homologous chromosomes does not occur
Meiosis: pairing of homologous chromosomes may occur
Mitosis:daughter cells are genetically identical to the parent cell
Meiosis: daughter cells are not genetically identical to the parent cell
Mitosis: 2 daughter cells are produced from 1 parent cell
Meiosis: 4 daughter cells are produced from 1 parent cell
Mitosis:involves 1 nuclear division
Meiosis: involves 2 nuclear divisions
Mitosis:occurs in normal body cells during growth/repair of body parts
Meiosis:occurs only in the gonads during gamete formation
In which stages in meiosis results in increased genetic variation?
Crossing over of homologous chromosomes to produce new chromosomes of alleles along the chromosome in prophase 1
Independent assortment of chromosomes at metaphase 1
Random fertilisation of gametes
