Unit 1.6 - Genetic information is copied and passed on to daughter cells Flashcards
What does cell division start from?
1 cell
What’s cell division essential for?
The development of ALL organisms
What’s essential for the development of all organisms?
Cell division
What are the two types of cell division?
Mitosis and meiosis
What does mitosis form?
All cells (apart from gametes)
What does meiosis form?
Gametes
Why is cell division important for maintaining the body?
Cells have a lifespan and don’t last forever
List the steps involved in a cell’s life cycle
Start
G1
R
S
G2
What are G1, R, S and G2 steps in?
Cell division
What is cell division to a cell’s entire life?
Only a small section
What’s the starting point of a cell’s lifespan?
Where a new cell has formed via cell-division
What happens at the G1 stage of a cell’s lifespan?
Cell is increasing in size
At which stage in a cell’s lifespan is it increasing in size?
G1
What happens at the R stage of a cell’s lifespan?
Cell decides whether to remain in G1 or to replicate
At which stage in a cell’s life cycle does a cell decide whether to replicate or remain in G1?
R
What do most cells do once they react the R stage of its life cycle? Why?
Remain in G1 once they’ve specialised, as they’re unlikely to divide again
What are most cells by the G1 stage and what does this mean?
Specialised, meaning they’re unlikely to divide again
What happens at the S stage of the cells lifecycle?
DNA replciation
Where does DNA replication occur in a cell’s life cycle?
S stage
What happens at the G2 stage of a cell’s lifecycle?
It synthesises organelles (prepares for cell division)
At which stage in a cell’s life cycle does it synthesise organelles and prepare for cell division?
G2
From which stages in DNA replication is interphase?
G1-G2
What’s the period from G1-G2 in a cell’s lifecycle known as?
Interphase
What can we see under a microscope during interphase?
Nothing -no visible changes
In which stage of a cell’s life cycle are there no visible changes?
Interphase
List 4 events of interphase
Protein synthesis
DNA replication (s)
Synthesis of new organelles
Increase in cell size
When do the following events all occur?
Protein synthesis, DNA replication, synthesis of new organelles, increased in cell size
Interphase
Why is it necessary for all of these procedures to take place during interphase?
Following cell division, the cell has half of everything except DNA which is an exact copy
What’s the only thing a cell doesn’t have half of following cell division?
DNA, which is an exact copy
Describe DNA during interphase
In the nucleus in the form of chromatin
During which stage in a cell’s lifespan is the DNA in the nucleus in the form of chromatin?
Interphase
What does chromatin do as we enter into mitosis?
Condenses to form chromosomes
What condenses to form chromosomes when entering into mitosis?
Chromatin
When does chromatin condense to form chromosomes?
Entering into mitosis
How many pairs of chromosomes are in every human cell?
23
What do we have 23 of and where?
PAIRS of chromosomes in our cells
What are the only cell’s in the body that don’t have 23 pairs of chromosomes? How many do they have?
Gametes, which have 23 EACH
How many chromosomes are in gametes and how does this make them different?
23 each, whereas all of the other human cells have 23 pairs
What do chromosomes exist as? What does this mean for them?
Homologous pairs, so they have very similar shapes
What exist as homologous pairs?
Chromosomes
What are the only chromosomes which don’t exist as homologous pairs?
X and Y
What do X and Y not exit as?
Homologous pairs of chromosomes
Why do chromates exist in homologous pairs?
The first cell was fertilised by an egg containing 1/2 the necessary chromosomes, and a sperm cell containing the other 1/2, together forming 23 pairs
What’s similar between two chromosomes in a homologous pair?
They have the exact same genes in the exact same locations which code for the same thng
What have the exact same genes?
Two chromosomes in a pair
How are the genes in chromosome pairs different?
They’re not - they could be different alleles of the gene though (e.g - BLUE eyes, not just eye colour)
What could be different alleles? Give an example
Genes that code for something specific
E.g - gene for eye colour
Different alleles = brown or blue or green eyes
Karotype
The preparation of the complete set of metaphase chromosomes in a cell
The preparation of the complete set of metaphase chromosomes in a cell
Karotype
Which phase are the chromosomes in in a Karotype?
Metaphase
What do chromosomes contain?
Long sections of DNA, proteins and a small amount of RNA
What do genes run along the length of?
Chromosomes
What run along the length of chomomes?
Genes
When are chromosomes visible?
On the onset of cell division
What are only divisible on the onset of cell division?
Chromosomes
How is DNA packed inside the nucleus?
Wrapped around histone protein molecules, which are condensed together to form chromatin fibres
What are condensed together to form chromatin fibres?
DNA wrapped around histone protein molecules
Chromatids
An identical thread of DNA from a copy itself
An identical thread of DNA from a copy of tself
Chromatid
What are joined together to form a chromosome and by what?
Chromatids, by a centromere
What does a centromere do?
Join chromatids together to form a chromosome
What do chromatids do?
Join together to form a chromosome
When does each DNA molecule make a copy of itself?
Shortly before cell division
What does DNA do shortly before cell division?
Makes a copy of itself
What happens to chromatids when a cell divides?
Chromatids are pulled apart into the new cells, ensuring that the new cell gets an exact copy of all of the genes on the DNA molecule
Draw and label a chromosome
(Check notes)
What are the 4 stages of mitosis?
Prophase
Metaphase
Anaphase
Telophase
Draw and label the prophase of mitosis
(Check notes)
Draw and label the metaphase of mitosis
(Check notes)
Draw and label the anaphase of mitosis
(Check notes)
Draw and label the telophase of mitosis
(Check notes)
What’s the longest stage of mitosis and what can be done therefore?
Prophase
Can be split into prophase and prometaphase
What happens during the prophase of mitosis?
The DNA (chromatin) condenses to form chromosomes
Chromatids become visible
In animal cells, the centrioles move to opposite poles of the cell
Protein microtubules form from each centriole and the spindle develops, extending from pole to pole
Towards the end, the nuclear membrane disintegrates and the nucleolus dissappears
Pairs of chromatids can clearly be seen lying free in the cytoplasm
In what type of cell alone do centrioles move to the opposite poles of the cell?
Animal cells
What do animal cells do during the prophase?
The centrioles move to opposite poles of the cell
In which stage of mitosis do chromatids become visible?
Prophase
What become visible during the prophase of mitosis?
Chromatids
When can pairs of chromatids be seen clearly in the cytoplasm?
Prophase
What forms from each centriole to the other during prophase?
Protein microtubules
At which stage does the nuclear membrane of a cell disintegrate and its nucleolus disappear?
Towards the end of the prophase
What do the chronometer attach to during mitosis and with what?
The spindle fibres, at the centromere
What happens during the metaphase of mitosis?
The chromosomes arrange themselves at the centre or equator of the spindle
Chromosomes become attached to the spindle fibres at the centromere
Contraction of the spindle fibres draws the individual chromatids apart
What type of fibres are the spindle fibres?
Contractile proteins
Where do chromosomes arrange themselves and during which stage of mitosis?
At the equator or centre of the spindle during the metaphase
What draws the individual chromatids apart during the metaphase of mitosis?
Contraction of the spindle fibres
What happens during the anaphase of mitosis?
Centromere splits
Spindle fibres contract and shorten
Chromatids separate and are pulled to opposite poles of the cell
Centromeres lead the way
Which phase of mitosis occurs fastest?
The anaphase
How are chromatids separated during mitosis and in which stage?
When the spindle fibres contract and shorten during the anaphase
What lead the way during the anaphase of mitosis?
Centromeres
Cytokinesis
Cell splitting - divide the cytoplasm of the parental cell into two daughter cells
Cell splitting
Cytokinesis
When does cytokinesis occur during mitosis?
At the telophase
What happens during the telophase of mitosis?
Chromatids have reached the poles and are referred to as chromosomes again
Chromosomes uncoil and lengthen
Spindle breaks down
Nucleolus reappears
Nuclear membrane reforms
When are chromatids referred to as chromosomes again during mitosis?
When they’ve reached the poles during the telophase
In which stage of mitosis does the spindle break down?
Telophase
During which stage of mitosis does the nucleolus reappear?
Telophase
During which stage of mitosis does the nuclear membrane reform?
Telophase
What do chromosomes do during the telophase of mitosis?
Uncoil and lengthen
Draw the stages of mitosis as they would appear under a microscope
(Check notes)
What’s proportional to the % of cells in each stage of cell division?
The length of the stage
What’s proportional to the length of the stage during mitosis?
The % of cells in each stage of the cell cycle
Where’s a good place to find dividing cells?
The meristem (root tip)
Root tip
Meristem
Meristem
Root tip
What’s the meristem (root tip) good for?
Finding dividing cells
What are added to root tip cells in order to see mitosis? Why?
Acetic orcein stain and hydrochloric acid to macerate the tissue
How do we macerate the tissues of meristem to see mitosis occurring?
With acetic orcein stain and hydrochloric acid
What does adding acetic orcein and hydrochloric acid do to the tissue of a meristem?
Macerates it
What do we do after macerating the tissue of a meristem with acetic orcein stain and hydrochloric acid?
Put on slide, heat gently and squash gently
What is acetic orcein?
A type of stain for microscopy
What is the main significance of mitosis?
Ensures that every cell is genetically identical and contain the same genes
Whats given form a mother cell to a daughter cell during mitosis?
An entire set of DNA institutions - the genome
Genome
The entire set of DNA instructions
The entire set of DNA instructions
Genome
Why must a cell contain the entire genome of that species?
In order to have all of the relevant genes, which they can switch on and off when needed
How can a cell contain all of the genes that it needs?
The genome must be passes on via mitosis
How does mitosis give genetic stability?
Genetic information is copied faithfully between generations
What does the fact that mitosis copies genetic information faithfully between generations mean for us?
We get genetic stability
Significance of mitosis
Growth
Replacement of lost cells
Reproduction
Explain how mitosis is important for growth
Multicellular organisms grow by mitosis
Each organism begins form a single cell which divides repeatedly via osmosis
What type of organisms grow by mitosis?
Multicellular organisms
What does each organism begin as?
A single cell
How can cells be lost?
Injury
Disease
Natural causes (e.g - shedding of skin cells)
Explain how mitosis is important for the replacement of old cells
When lost through injury or disease or natural causes, cells are replaced by genetically identical cells
What type of reproduction occurs via mitosis?
Asexual
Explain how mitosis is important for reproduction
Asexual reproduction of single called organisms, many plants and even some animals
What do cancers form from?
DNA mutations from normal cells
What are the stages that lead to cancer via DNA mutations?
Normal cell —> DNA mutations —> Uncontrolled proliferation
Can 1 mutation in a cell lead to a cancer?
No, it comes from multiple mutations
What’s required for a cancer to form?
Multiple mutations
Why do cancers not usually form?
The cell is usually able to convert the change, but there are occasional slips in the system
What could DNA mutations form from?
Heredity
Radiation or chemicals
Spontaneous errors during DNA replication
What could radiation or chemicals lead to?
DNA mutations
How does a tumour form?
Uncontrolled mitosis causes cancerous cells to divide repeatedly
What does uncontrolled mitosis casing cancerous cell to divide repeatedly cause?
A tumour forms
Tumour
An irregular mass of cells which prevent the normal function of body organs
An irregular mass of cells which preen the normal function of body organs
Tumour
What are three differences between mitosis in animal and plant cells?
Plant = no centriole, so the spindle isn’t generated by them but is in animal cells
Spindle remains as the new cell wall is formed in plant cells, but degenerates at telophase for animal cells
Cell plate forms between the 2 new nuclei and develops into the new cell wall in plant cells, but cytokinesis forms a cleavage furrow where the cytoplasm indents in animal cells
What type of cells don’t contain a centriole for forming spindles?
Plants cells
In what type of cells does the spindle degenerate and at which phase?
Animal cells at telophase
What happens to the spindle in plant cells?
Remains as the new wall is formed
What type of cells does cytokinesis occur in?
Animal cells
What forms between the 2 new nuclei in plant cells mitosis?
A cell plate which develops into a new cell wall
Where does meiosis occur?
In reproductive organs that produce gametes
What type of cell division occurs in reproductive organs that produce gametes?
Meiosis
How many chromosomes do gametes have?
1/2 the normal chromosome number (haploid number)
Haploid number (+give an example)
Half the normal chromosome number (e.g - gametes)
What do the cells produced during meiosis have?
Genetic variation
In what type of cell division do cells have genetic variation?
Meiosis
What does meiosis play an important role in?
Bringing out genetic variation in living organisms
What’s important for bringing out genetic variation in living organisms?
Meiosis
Diploid number formula
2n
2n formula
Diploid number
Haploid number formula
n
n formula
Haploid
How are gametes haploid cells?
They have 1 copy of each chromosome
How many chromosomes do humans have and in what form?
46 in 23 homologous pairs
What are the pairs that human chromosomes exist in?
Homologous pairs (23 of them)
What are human cells generally?
Diploid cells - contain 2 copies of each chromosome
What do gametes do at fertilisation and how does this affect haploid and diploid numbers?
Fuse, restoring the diploid number
When is the diploid number restored for gametes?
During fertilisation
What does gametes being haploid cells ensure?
Ensures that the chromosome number of individuals remains the same from generation to generation
Why is each cell genetically different following meiosis?
Crossing over
Random assortment
What does crossing over and random assortment cause in cells?
Causes them to be genetically different
Why is cells being genetically different essential for survival?
During changes in Environmental conditions, som of the offspring will have variations that enable them to survive, increasing the species’ chance of survival
What’s the whole first set of meiosis stages known as?
First meiotic division (meiosis I)
What is essentially occurring during meiosis I?
Separation of homologues
What’s the first stage of meiosis I, and what happens here?
Prophase I
Chromatin condenses and chromosomes become visible as 2 sister chromatids joined by a centromere
Chromosomes join up in homologous pairs and lie side by side, forming bivalents
When doing this, they swap pieces of sister chromatids with each other (crossing-over)
In animal cells, the centrioles migrate to the poles
Spindle forms, nuclear membrane disintegrates
What forms a bivalent and during which stage of meiosis I?
During prophase I, chromosomes joining up in homologous pairs
How can we recognise bivalents in prophase I?
4 arms
What do 4 arms represent (meiosis)?
Bivalents, during prophase I
What does crossing-over lead to?
Genetic variation between generations
What type of process is crossing - over?
Random
Describe the process of crossing over (+ which stage of meiosis does this occur?)
During prophase I…
Chromosomes in a homologous chromosome pair move closer together
Synapsis occurs
(Connections - chiasmata)
Chromatids break and genetic information is exchanged
What’s the name for the connections formed during the crossing over stage of prophase I?
Chiasmata
Chiasmata
The connections formed between homologous chromosome pairs during the crossing over stage of prophase I in meiosis
What occurs when chromosomes move closer together during the crossing over stage during prophase I?
Synapsis
What type of chromosomes exchange genetic information during crossing over?
Homologous chromosome pairs
Why does crossing over work?
Genes are in the same places on the chromosomes, but could be different alleles/versions of the gene
Allele
Version of a gene
Different versions of a gene
Alleles
What do chromosomes have different combinations of following crossing over?
Alleles
In what type of cells do centrioles migrate to the poles?
Animal cells
Which stage of prophase I occurs in animal cells alone?
Centrioles migrate to the poles
What happens during metaphase I of meiosis?
The bivalents migrate to the equator of the cell
Attach to the spindle by the centromeres
However they arrange themselves along the equator is random and independent of one another (independent/random assortment)
How do bivalents attach to the spindle?
By the centromeres
Independent assortment
However bivalents arrange themselves along the equator of a cell (its random and independent of one another)
However bivalents arrange themselves along the equator of a cell (its random and independent of one another)
Independent assortment
How do we work out the amount of types of gametes that can form through independent assortment?
2^n, where n is the total amount of pairs of chromosomes
How many different possible combinations of chromosomes can human cells have from independent assortment? (show your working out)
2n = possible types of gametes
n = pairs of chromosomes
n = 23
2^23 = 8,388,608
What’s the possibility of 2 identical gametes in 2 people?
Practically zero
The possibility of 2 identical what in two people is practically zero?
2 identical gametes
What happens during anaphase I?
Spindle contracts
Pulls chromosomes towards each pole
They’re pulled away from their bivalent, while the chromatid stays together
Each chromosome is still composed of 2 chromatids, but they’re not genetically identical because of crossing over
During anaphase I, what are the chromosomes pulled away from and what stays together?
Chromosomes are pulled away from their bivalent
Chromatid stays together
Following anaphase I, what condition are chromosomes in?
Each chromosome is still composed of 2 chromatids, but they’re not genetically identical because of crossing over
What happens during telophase I?
Chromosomes reach the poles
Nuclear membranes reform
1 of each homologue pair of chromosomes per cell
Cytokinesis - forms 2 cells, each with a haploid nucleus
What happens following cytokinesis in telophase I?
2 cells form, each with a haploid nucleus
What has happened to the number of chromosomes per cell following telophase I?
Halved
What’s the number of chromosomes before telophase I known as?
Diploid number
What’s the number of chromosomes following telophase I known as?
Haploid number
Why is the number of chromosomes in the new cells following telophase I half the original amount?
Chromosomes are no longer paired
Diploid number
Total chromosomes
Haploid number
1/2 total chromosomes
What’s the name for the second stage of meiosis?
Second division of meiosis (meiosis II)
What essentially occurs during the second division of meiosis?
Sister chromatids are separated (by mitosis)
Is there DNA replication between the two divisions of meiosis?
No
What occurs during prophase II of meiosis?
Chromosomes condense - they become visible as 2 chromatids joined by a centromere
Spindle reforms (after being broken down during cytokinesis)
Nuclear membranes disintegrate
What is broken down during cytokinesis and in which stage of meiosis does it reform
The spindle
Reforms during prophase II
What occurs during metaphase II?
Chromosomes migrate to the equator
Attach to the spindle by the centromere
Chromatids are not identical - each one in the chromosomes can orientate towards a pole randomly - independent assortment
How can the chromatids move towards the pole and why?
Randomly, as they’re not identical in metaphase II
When does independent assortment occur in meiosis?
Metaphase I and II
What occurs during anaphase II?
Centromeres divide as the chromatids are pulled to the poles by contraction of the spindle
Chromatids are now called chromosomes
How are chromatids pulled to the poles of the cells?
By contraction of the spindle
What happens during telophase II in meiosis?
Chromosomes reach the poles and the nuclear membranes reform
Cytokinesis - each cell divides, forming 2 daughter cells
Gametes are haploid cells, contain only 1/2 the amount of the original chromosomes
By which stage are haploid cells formed during meiosis?
Telophase II
Why do gametes have to be haploid cells?
When they join during fertilisation, we need to form a diploid cell to form the zygote
What is formed when gametes join and what is this process known as?
A zygote, during fertilisation
What type of cell is a zygote?
Diploid cell
Describe the gametes formed during telophase II of meiosis
Genetically varied
Why are gametes genetically varied?
Mixed chromosomes, which contain different combinations of alleles
Make 6 comparisons between mitosis and meiosis
(Check table in notes)
Compare division between mitosis and meiosis
Mitosis - 1 division resulting in 2 daughter cells
Meiosis - 2 divisions resulting in 4 daughter cells
Compare the genetic similarity of the cells during mitosis and meiosis
Mitosis - genetically identical daughter cells
Meiosis - not genetically identical daughter cells (due to crossing over in prophase I and independent assortment in metaphase I and II)
Why are the daughter cells formed during meiosis not identical (+ state the stages in which these occur)
Crossing over (prophase I)
Independent assortment (metaphase I and II)
Compare he number of chromosomes in the daughter cells following mitosis and meiosis
Mitosis - number of chromosomes is unchanged
Meiosis - number of chromosomes is halved
Compare the situation of homologous chromosomes in mitosis and meiosis
Mitosis - homologous chromosomes do not associate in pairs
Meiosis - homologous chromosomes pair up to form bivalents (Synapsis)
Compare the crossing over situation across mitosis and meiosis
Mitosis - no crossing over
Meiosis - crossing over occurs and chiasmata form
Compare the cells which are involved in the process of mitosis and meiosis
Mitosis - haploid and diploid cells - sister chromatids from each chromosome are separated into new cells
(Haploid —> haploid)
(Diploid —> diploid)
Meiosis - can only occur in diploid cells - the homologous pairs form bivalent in prophase I
Where does meiosis occur in animals?
In the testes (sperm) or the ovaries (egg)
Where does meiosis occur in plants?
In the anther (pollen formation) or the ovule (egg cell)
Why is the protein synthesis stage of interphase important?
for the formation of a spindle from protein microtubules
Define a diploid
an organism with 2 complete sets of chromosomes
An organism with 2 complete sets of chromosomes
Diploid
Homologous chromosomes
the same size and shape and carry the same genes, but may be different alleles
the same size and shape and carry the same genes, but may be different alleles
Homologous chromosomes
What’s the only difference in homologous chromosomes?
different alleles
What happens during cytokinesis?
the cytoplasm divides
when does a cytoplasm divide?
during cytokinesis
Polyploidy
where an organism has more than two complete sets of chromosomes
where an organism has more than two complete sets of chromosomes
polyploidy
RNA polymerase function
Catalyses the formation of a new mRNA molecule - moves along the coding DNA strand (the bottom strand), forming bonds that add nucleotides one at a time to the RNA (pre-mRNA)
What’s the difference between mitosis and meiosis during prophase?
Mitosis - no homologous chromosome pairs, bivalents and no Synapsis
Meiosis - all of the above occur
What does using a stain in an experiment do?
Stain the DNA
What makes DNA easier to see in an experiment?
Staining
What are the differences between anaphase I and II?
Anaphase I
Homologous chromosomes separate
Centromeres don’t divide
Diploid
Anaphase II
Chromatids separate
Centromeres divide
Haploid
What do we NOT say during the period in which a cell increases in size during interphase?
That it’s grown
What’s DNA present as following interphase?
Chromosomes
Synapsis
Fusion of chromosome pairs at the start of meiosis
Fusion of chromosome pairs at the start of meiosis
Synapsis
When does Synapsis occur?
At the start of meiosis
Name some locations in the body where more mitosis is likely to be observed and explain why this is the case
Skin (stem) cells
Bone marrow (stem) cells
Gut lining
Liver cells
New cells are being made as they’re worn away rapidly and need to be replaced
What happens to the quantity of DNA following cytokinesis?
Halves
What does asexual reproduction produce and via what?
Clones, via mitosis
When does crossing over occur?
Prophase I
When does random assortment occur?
Metaphase I and II
What do photo encogenes do?
Act as a brake on cell division
If mutated, there’s no brake, so we get uncontrolled cell division
What act as a break on cell division?
Photo encogenes
The cell cycle
Cellular events that repeat in order between 1 cell division and the next
Why do we get infertile offspring if 2 parents have a different number of chromosomes?
Chomosomes can’t form homologous pairs
Meiosis isn’t possible
No gametes form
