Cell division: Mitosis and Meiosis Flashcards
What is the cell cycle
The series of events that takes place in a cell that results in DNA replication and cell division
What are the two main stages in the cell cycle and what occurs in each
The first stage is interphase during which the cell grows and replicates its DNA. Thet second phase is mitotic phase/ M phase/ Division phase during which the cell divides and transfers one copy of its DNA to two identical daughter cells
What is the role of mitosis
New cells are formed in order to ensure that the organism grows and increases in size and also to ensure that worn out or damaged cells are repaired and replaced.
Mitosis results in asexual reproduction in some simple plants and animals
What is interphase
The period between two consecutive cell divisions
How do the chromosomes look during interphase
The chromosones are visible as the chromatin network
Interphase is the _____ phase of the cell cycle
Longest
What perecentage of the cell cycle are is used for interphase and mitosis
Interphase accounts for approximately 90% of the cell cycle and for mitosis 10%
What are the 3 phases within interphase
G1, G2 and S phase
Explain what occurs in G1 phase
It occurs after the two daughter cells have split and cells have only one copy of their DNA.
Cells in this stage synthesise proteins and increase in size.
Cells can remain in this stage for a long time.
Explain what occurs in S phase
It is the stage during which DNA replication occurs.
The cell makes an identical copy of each of its chromosomes.
Chrromosomes are found inside the nucleus of the cell and consist of long strands of DNA that contain the cell’s genetic information
Explain what happens in G2 phase
Occurs after the DNA has been replicated in S phase.
Cells may continue to grow and undergo normal cellular functions.
Towards the end of this phase the cell may start to replicate its organelles in preparation for mitosis.
Explain what happens in G0 phase
Some cells no longer need to divide and exit the cell cycle (they are said to be in G0) and may do this permanently such as neurons, or they may do so temporarily. G0 is not a stage of the cell cycle
What are chromosomes
Thread like structures found in the cell nucleus of virtually all cells
What do chromosomes do
They transfer hereditary characteristics from generation to generation
What do chromosomes appear as when the cell is not dividing
It appears as a mass of threads (the chromatin network)
What do chromosomes look like when the cell is dividing
The chromatin network condenses, the threads become shorter and thicker and visible as single stranded chromosomes
What do chromosomes consist of
Thye consist of the nucleic acid, DNA that is wrapped helically around proteins known as histones
What are the various DNA segments along the length of each chromosome known as and what do they do
They are genes and each one controls a specific hereditary characteristic
True or Flase:
After a cell divides all genetic material in the nucleus (DNA) has to be duplicated.
False.
Before a cell divides all genetic material in the nucleus has to be duplicated.
What is replication
The process during which the DNA molecule makes an identical replica of itself
Why is replication necessary
To ensure that both daughter cells formed during mitosis have exactly the sam genetic information as in the original mother cell
After replication what happens to the chromosome
The single stranded chromosome (DNA and histones) now consists of two identical chromatids. The two chromatids of the new double stranded chromosomes are joined together by a centromere
What are the two stages of mitosis
Karyokinesis: division of the nucleus and chromosomes
Cytokinesis: Division of the cytoplasm, organelles and cell membrane.
What are the four phases that occur during the process of mitosis
Prophase, Metaphase, Anaphase, Telophase
Explain what occurs during prophase
The chromatin network condenses, the threads become shorter and thicker and visible as chromosomes.
Chromosomes are double stranded because they were replicated during interphase.
Each chromosome has two identical chromatids that are joined by a centromere.
Nuclear membrane and nucleolus disappear.
The centrioles separate and move to opposite poles of the cell.
Spindle fibres (protoplasmic threads) form between the two centrioles to form the spindles
Explain what occurs during metaphase
The chromosomes move to the equator and arrange themselves in a single row on the equator of the cell.
Spindle fibres attach to the centromere
Explain what occurs during anaphase
Spindle fibres shorten.
The centromere of each chromosome divides into two
The two chromatids separate from each other and move to opposite poles.
The chromatids are now known as daughter chromosomes.
Centromeres are positioned towards the poles.
Cytokinesis (division of the cytoplasm) begins
Explain what occurs during telophase
The daughter chromosomes arrange themselves at the pole.
Spindle fibres disappear.
Nuclear membrane forms around the daughter chromosomes.
Nucleolus forms in each nucleus.
Karyokinesis is complete and cytokinesis occurs ( cytoplasm divides)
In animal cells invagination occurs in the cytoplasm at the equator.
In plant cells a cell plate/ transverse wall forms in the cytoplasm at the equator
Cytokinesis is now complete and two identical daughter cells are formed.
Both new nuclei (daughter nuclei) contain the same number of chromosomes as the original mother nucleus.
Give the definition for mitosis
The division of somatic (body) cells. Mitosis produces two daughter cells from the mother cell with exactly the same number of chromosomes
Give the definition for meiosis
Formation of gametes (sex cells) in animals or spores in plants. The daughter cells formed from meiosis have only one set of chromosomes (n) and are not identical to each other or to the original mother cell.
Give the definition for DNA
Deoxyribonucleic acid is an organic chemical that contains genetic information and instructions for protein synthesis
Give the definition for genes
a DNA segment of a chromosome that determines a particular hereditary characteristic
Give the definition for chromosomes
an organised package of DNA found in the nucleus of the cell
Give the definition for chromatids
condensed strand of DNA, a replicated chromosome has two chromatids - thus two identical copies of DNA for cell division
Give the definition of a telomere
The caps at the end of each strand of DNA that protect our chromosomes.
Give the definition of a centromere
The specialised DNA sequence of a chromosome that links a pair of sister chromatids
Give the definition for kinetochore
a disc shaped protein structure associated with duplicated chromatids in eukaryotic cells where the spindle fibres attach during cell division to pull sister chromatids apart
Give the definition for spindle fibres
microscopic protein structures that help divide genetic material during cell division and organise cellular components. The spindle fibres form out of the centrosome
Give the definition for sister chromatids
two identical copies of the same chromosome formed by DNA replication , attached to each other by the centromere
Give the definition for homologs
chromosomes carrying the same information from the other parent
Give the definition for diploid
Describes a cell or nucleus which contains two copies of genetic material, or a complete set of chromosomes, paired with their homologs
Give the definition for haploid
the quality of a cell or organism having a single set of chromosomes
Define mutation
the change that occurs in our DNA sequence , either due to mistakes when the DNA is copied or as the result of environmental factors such as UV light and cigarette smoke.
Define cancer
uncontrolled cell division
Define cloning
the process of producing individuals with identical or virtually identical DNA either naturally or artificially
Give the definition for karyotype
The complete diploid set of chromosomes, arranged according to their size, shape and number in homologous pairs, within a somatic cell of an organism
What is the human diploid chromosome number
46
What is the human haploid chromosome number
23
What does the human karyotype consist of
22 pairs of autosomes (44 ordinary chromosomes that are not involved in sex determination) and one pair of gonosomes (2 sex chromosomes) known as X and Y chromosomes
What is the chromosome composition in males and females.
females 44+ XX
males 44+ XY
What is the result of uncontrolled mitotic cell division in the body
cancer
What happens when cancer forms
A group of cells is formed that lose their original function. After repeated divisions a mass of tissue is formed referred to as a growth/tumour
What is the difference between a benign and malignant tumour
A benign tumour does not penetrate the tissues and is usually enclosed in a capsule
A malignant tumour spreads between the cells of the tissue, damaging them
How can new tumours form in other parts of the body
The cancerous cells are spread by the circulation of the blood
What are the main types of cancer and elaborate
Carcinomas: arise in the epithelial tissue that lines the skin and the internal organs of the body
Sarcomas: Occur in the connective tissue, and the muscle, fat, bone, cartilage, blood and lymph vessels that make up the structure of the body
What do we call something that causes cancer
a carcinogen or a carcinogenic agent
What are possible carcinogenic agents
cigarette smoke, exposure to certain chemicals like asbestos, sun, pollutants, radiation such as x rays, hormonal imbalances, hereditary factors
What are treatments for cancer
tumours can be surgically removed, chemotherapy (the use of chemical agents) and radiography (through radioactive radiation)
What is cloning
The process in which a genetically identical replica of a molecule (eg. DNA), cell or entire organism is made
What are the types of cloning
DNA cloning, reproductive cloning and therapeutic cloning
Explain DNA cloning
The transfer of a part of DNA (a gene) from an organism to a foreign host cell to obtain a desired characteristic
Explain reproductive cloning
This is the creation of an organism that contains the same DNA as another living or dead organism. The most well known example is dolly the sheep, the first mammal cloned from a fully grown somatic cell in 1997
Explain therapeutic cloning
It is also known as embryo cloning. Human embryos are cloned for stem cell research
What are stem cells
Undifferentiated cells in the human body that have the ability to differentiate into virtually any type of specialised cell
Where are stem cells obtained from
Human embryos and the umbilical chord of a newborn baby (embryonic). They can increase indefinitely through mitosis. They are able to differentiate into any type of specialised cell, even sperm or ovum cell.
Various organs eg. bone ,marrow (adult stem cells). It cannot differentiate into any type of specialised cell.
What can harvested stem cells be used for
to study human development
to replace damaged tissue and organs
to treat diseases such as leukaemia, diabetes and Alzheimer’s
What is vegetative propagation
Any form of asexual reproduction where a new plant is generated from a fragment of the parent plant or from a specialised reproductive structure (such as stolon, rhizome, tuber, corn or bulb . It can occur naturally or be induced. It takes place through mitosis. The new organisms are genetically identical to their parents and are called clones
What are bulbs in a plant
big round stems surrounded by special leaves eg. freesias and onions
What are runners/stolons in a plant
long, thin stems that go across the ground eg. hen and chicken grass
What are rhizomes
underground stems eg. bananas
What are stem tubers
thickened rhizomes eg. potato
What are root tubers
Swollen lateral roots eg. sweet potatoes
What are suckers
They develop from roots into a new plant eg. a tree called pendoring (Gymnosporia buxifolia)
What are the advantages of asexual reproduction
- Only one parent is needed and all individual plants can reproduce
- No special organs of reproduction such as flowers are required
- New plants are produced quickly as only mitosis is involved, followed by growth. This is of great value as new plants can be propagated simply, quickly and cheaply
- No outside agents such as pollinators are needed to complete the process.
- Very little energy is used for this type of reproduction eg. no reproductive structures have to be made.
- The new plants are genetically identical, there is no variation. This maintains that successful variations are produced
- Asexual reproduction is very useful in unchanging and stable conditions.
- A favourable mutation can spread rapidly, enabling the population to adapt quickly to any new environmental conditions
- By avoiding seed dormancy, plants can be propagated throughout the year independent of seasonal changes
`What are the disadvantages of asexual reproduction
- Asexual reproduction does not give rise to variation as there is no mixing of the genetic material. The species could not adapt to new environmental conditions and could die out
- Genetic weaknesses cannot be bred out and will be passed onto offspring
Describe meiosis
A type of cell division that produces four different haploid daughter cells (gametes in animals and spores in plants). It is known as reproduction division as the chromosome number is halved in the daughter cells (diploid to haploid)
What are the stages of meiosis and briefly explain what happens in them
- First meiotic division/ meiosis I
During the first meiotic division, the chromosome number is halved and the genetic material is exchanged to produce genetic variation
2n-> n - Second meiotic division ? meiosis II
The second meiotic division proceeds like normal mitosis where the sister chromatids separate from each other
n-> n
What are the phases of meiosis I
Prophase I, Metaphase I, Anaphase I, Telophase I
What happens during prophase I
The chromatin network condenses, the threads become shorter and thicken to become visible as chromosomes.
Although replication has already occurred, separate chromatids can not yet be distinguished.
The homologous chromosomes arrange themselves in pairs. The two chromosomes of each homologous pair lie in contact to from a bivalent which look like single chromosomes of double thickness. Each one contains 4 homologous chromosomes (4 sister chromatids).
In late prophase each homologous chromosome of the bivalent becomes visible as two chromatids joined by a centromere. These identical chromatids of a single chromosome are sister chromatids, the centromeres do not divide
Overlapping occurs between adjacent chromatids of a pair of homologous chromosomes.
Crossing over occurs between the adjacent chromatids when segments (groups of genes) break off and are exchanged at the point called the chiasmata
Nucleus and nuclear membrane disappear
In animal cells the centrosome splits and pairs of the centrioles move to opposite poles of the cell
Spindle fibres develop between the centrioles to form the spindle
What is the singular form of the chiasmata
chiasma
How does the crossing over of adjacent chromatids of a pair of homologous chromosomes during prophase I introduce genetic variation
By reshuffling or recombination of genetic material between maternal and paternal chromosomes
What happens during metaphase I
The homologous pairs of chromosomes position themselves randomly on the equator in a double row
One of the chromosomes of each pair lies on either side of the equator
Spindle fibres attach to the centromeres
What happens during anaphase I
The spindle fibres contract and shorten, pulling the chromosomes towards the poles
Chromosomes of a homologous pair are separated from each other
One chromosome of a homologous pair moves towards one pole and the other moves towards the opposite poles
Cytokinesis begins
What happens during telophase I
The chromosomes group themselves at the poles
The spindle fibres disappear
A nuclear membrane forms around each group of chromosomes and a nucleolus forms in the nucleus
Cytokinesis is complete after invagination (animal cells) or cell plate (plant cells) and two daughter cells are formed
Each daughter cell has half the chromosome number (n) of the mother cell (2n)
The chromosomes in each daughter cell have two chromatids joined by a centromere with exchanged genetic material (recombinant chromatids)
What happens in meiosis II
Both daughter cells formed during meiosis I will undergo a further division during meiosis II
What happens in prophase II
Each chromosome consists of two recombinant chromatids (with exchanged genetic material) joined by a centromere
There are no homologous pairs
The nucleolus and nuclear membrane disappear
A spindle form consisting of centrioles at opposite poles joined by the spindle
What happens in metaphase II
The chromosomes move to he equator and align randomly in a single row on the equator
Spindle fibres attach to the centromeres
What happens in anaphase II
The spindle fibres shorten
The centromere of each chromosome splits
Th two sister chromatids separate and move to opposite poles
The single chromatids (daughter chromosomes) form V shapes as the centromere is pulled by the spindle fibres
Cytokinesis begins
What happens in telophase II
The chromatids (daughter chromosomes) group at the poles and are known as unreplicated chromosomes
The unreplicated chromosomes in each daughter cells are also known as recombinant chromatids as they have exchanged genetic material
The spindle fibres disappear
Nuclear membrane forms around each group of unreplicated chromosomes and the nucleolus reforms
Cytokenisis occurs
In animal cells invagination occurs in plant cells a cell plate forms, dividing the cytoplasm at the equator
Cytokinesis is complete and four daughter cells have been formed , each with the haploid chromosome number
Due to crossing over (exchange of genetic material), the daughter cells are genetically different
In males the daughter ells develop into sperm
In females, three of the daughter cells disintegrate and one develops into an egg/ ovum
Fill in the missing words
The 4 daughter cells formed at the end of meiosis will always have _________and chromatids with _________
The 4 daughter cells formed at the end of meiosis will always have half the chromosome number and chromatids with only the exchanged genetic material
