Unit 1.6 - Genetic information is copied and passed on to daughter cells Flashcards
1
Q
What does cell division start from?
A
1 cell
2
Q
What’s cell division essential for?
A
The development of ALL organisms
3
Q
What’s essential for the development of all organisms?
A
Cell division
4
Q
What are the two types of cell division?
A
Mitosis and meiosis
5
Q
What does mitosis form?
A
All cells (apart from gametes)
6
Q
What does meiosis form?
A
Gametes
7
Q
Why is cell division important for maintaining the body?
A
Cells have a lifespan and don’t last forever
8
Q
List the steps involved in a cell’s life cycle
A
Start
G1
R
S
G2
9
Q
What are G1, R, S and G2 steps in?
A
Cell division
10
Q
What is cell division to a cell’s entire life?
A
Only a small section
11
Q
What’s the starting point of a cell’s lifespan?
A
Where a new cell has formed via cell-division
12
Q
What happens at the G1 stage of a cell’s lifespan?
A
Cell is increasing in size
13
Q
At which stage in a cell’s lifespan is it increasing in size?
A
G1
14
Q
What happens at the R stage of a cell’s lifespan?
A
Cell decides whether to remain in G1 or to replicate
15
Q
At which stage in a cell’s life cycle does a cell decide whether to replicate or remain in G1?
A
R
16
Q
What do most cells do once they react the R stage of its life cycle? Why?
A
Remain in G1 once they’ve specialised, as they’re unlikely to divide again
17
Q
What are most cells by the G1 stage and what does this mean?
A
Specialised, meaning they’re unlikely to divide again
18
Q
What happens at the S stage of the cells lifecycle?
A
DNA replciation
19
Q
Where does DNA replication occur in a cell’s life cycle?
A
S stage
20
Q
What happens at the G2 stage of a cell’s lifecycle?
A
It synthesises organelles (prepares for cell division)
21
Q
At which stage in a cell’s life cycle does it synthesise organelles and prepare for cell division?
A
G2
22
Q
From which stages in DNA replication is interphase?
A
G1-G2
23
Q
What’s the period from G1-G2 in a cell’s lifecycle known as?
A
Interphase
24
Q
What can we see under a microscope during interphase?
A
Nothing -no visible changes
25
In which stage of a cell’s life cycle are there no visible changes?
Interphase
26
List 4 events of interphase
Protein synthesis
DNA replication (s)
Synthesis of new organelles
Increase in cell size
27
When do the following events all occur?
Protein synthesis, DNA replication, synthesis of new organelles, increased in cell size
Interphase
28
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
29
What’s the only thing a cell doesn’t have half of following cell division?
DNA, which is an exact copy
30
Describe DNA during interphase
In the nucleus in the form of chromatin
31
During which stage in a cell’s lifespan is the DNA in the nucleus in the form of chromatin?
Interphase
32
What does chromatin do as we enter into mitosis?
Condenses to form chromosomes
33
What condenses to form chromosomes when entering into mitosis?
Chromatin
34
When does chromatin condense to form chromosomes?
Entering into mitosis
35
How many pairs of chromosomes are in every human cell?
23
36
What do we have 23 of and where?
PAIRS of chromosomes in our cells
37
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
38
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
39
What do chromosomes exist as? What does this mean for them?
Homologous pairs, so they have very similar shapes
40
What exist as homologous pairs?
Chromosomes
41
What are the only chromosomes which don’t exist as homologous pairs?
X and Y
42
What do X and Y not exit as?
Homologous pairs of chromosomes
43
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
44
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
45
What have the exact same genes?
Two chromosomes in a pair
46
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)
47
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
48
Karotype
The preparation of the complete set of metaphase chromosomes in a cell
49
The preparation of the complete set of metaphase chromosomes in a cell
Karotype
50
Which phase are the chromosomes in in a Karotype?
Metaphase
51
What do chromosomes contain?
Long sections of DNA, proteins and a small amount of RNA
52
What do genes run along the length of?
Chromosomes
53
What run along the length of chomomes?
Genes
54
When are chromosomes visible?
On the onset of cell division
55
What are only divisible on the onset of cell division?
Chromosomes
56
How is DNA packed inside the nucleus?
Wrapped around histone protein molecules, which are condensed together to form chromatin fibres
57
What are condensed together to form chromatin fibres?
DNA wrapped around histone protein molecules
58
Chromatids
An identical thread of DNA from a copy itself
59
An identical thread of DNA from a copy of tself
Chromatid
60
What are joined together to form a chromosome and by what?
Chromatids, by a centromere
61
What does a centromere do?
Join chromatids together to form a chromosome
62
What do chromatids do?
Join together to form a chromosome
63
When does each DNA molecule make a copy of itself?
Shortly before cell division
64
What does DNA do shortly before cell division?
Makes a copy of itself
65
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
66
Draw and label a chromosome
(Check notes)
67
What are the 4 stages of mitosis?
Prophase
Metaphase
Anaphase
Telophase
68
Draw and label the prophase of mitosis
(Check notes)
69
Draw and label the metaphase of mitosis
(Check notes)
70
Draw and label the anaphase of mitosis
(Check notes)
71
Draw and label the telophase of mitosis
(Check notes)
72
What’s the longest stage of mitosis and what can be done therefore?
Prophase
Can be split into prophase and prometaphase
73
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
74
In what type of cell alone do centrioles move to the opposite poles of the cell?
Animal cells
75
What do animal cells do during the prophase?
The centrioles move to opposite poles of the cell
76
In which stage of mitosis do chromatids become visible?
Prophase
77
What become visible during the prophase of mitosis?
Chromatids
78
When can pairs of chromatids be seen clearly in the cytoplasm?
Prophase
79
What forms from each centriole to the other during prophase?
Protein microtubules
80
At which stage does the nuclear membrane of a cell disintegrate and its nucleolus disappear?
Towards the end of the prophase
81
What do the chronometer attach to during mitosis and with what?
The spindle fibres, at the centromere
82
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
83
What type of fibres are the spindle fibres?
Contractile proteins
84
Where do chromosomes arrange themselves and during which stage of mitosis?
At the equator or centre of the spindle during the metaphase
85
What draws the individual chromatids apart during the metaphase of mitosis?
Contraction of the spindle fibres
86
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
87
Which phase of mitosis occurs fastest?
The anaphase
88
How are chromatids separated during mitosis and in which stage?
When the spindle fibres contract and shorten during the anaphase
89
What lead the way during the anaphase of mitosis?
Centromeres
90
Cytokinesis
Cell splitting - divide the cytoplasm of the parental cell into two daughter cells
91
Cell splitting
Cytokinesis
92
When does cytokinesis occur during mitosis?
At the telophase
93
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
94
When are chromatids referred to as chromosomes again during mitosis?
When they’ve reached the poles during the telophase
95
In which stage of mitosis does the spindle break down?
Telophase
96
During which stage of mitosis does the nucleolus reappear?
Telophase
97
During which stage of mitosis does the nuclear membrane reform?
Telophase
98
What do chromosomes do during the telophase of mitosis?
Uncoil and lengthen
99
Draw the stages of mitosis as they would appear under a microscope
(Check notes)
100
What’s proportional to the % of cells in each stage of cell division?
The length of the stage
101
What’s proportional to the length of the stage during mitosis?
The % of cells in each stage of the cell cycle
102
Where’s a good place to find dividing cells?
The meristem (root tip)
103
Root tip
Meristem
104
Meristem
Root tip
105
What’s the meristem (root tip) good for?
Finding dividing cells
106
What are added to root tip cells in order to see mitosis? Why?
Acetic orcein stain and hydrochloric acid to macerate the tissue
107
How do we macerate the tissues of meristem to see mitosis occurring?
With acetic orcein stain and hydrochloric acid
108
What does adding acetic orcein and hydrochloric acid do to the tissue of a meristem?
Macerates it
109
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
110
What is acetic orcein?
A type of stain for microscopy
111
What is the main significance of mitosis?
Ensures that every cell is genetically identical and contain the same genes
112
Whats given form a mother cell to a daughter cell during mitosis?
An entire set of DNA institutions - the genome
113
Genome
The entire set of DNA instructions
114
The entire set of DNA instructions
Genome
115
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
116
How can a cell contain all of the genes that it needs?
The genome must be passes on via mitosis
117
How does mitosis give genetic stability?
Genetic information is copied faithfully between generations
118
What does the fact that mitosis copies genetic information faithfully between generations mean for us?
We get genetic stability
119
Significance of mitosis
Growth
Replacement of lost cells
Reproduction
120
Explain how mitosis is important for growth
Multicellular organisms grow by mitosis
Each organism begins form a single cell which divides repeatedly via osmosis
121
What type of organisms grow by mitosis?
Multicellular organisms
122
What does each organism begin as?
A single cell
123
How can cells be lost?
Injury
Disease
Natural causes (e.g - shedding of skin cells)
124
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
125
What type of reproduction occurs via mitosis?
Asexual
126
Explain how mitosis is important for reproduction
Asexual reproduction of single called organisms, many plants and even some animals
127
What do cancers form from?
DNA mutations from normal cells
128
What are the stages that lead to cancer via DNA mutations?
Normal cell —> DNA mutations —> Uncontrolled proliferation
129
Can 1 mutation in a cell lead to a cancer?
No, it comes from multiple mutations
130
What’s required for a cancer to form?
Multiple mutations
131
Why do cancers not usually form?
The cell is usually able to convert the change, but there are occasional slips in the system
132
What could DNA mutations form from?
Heredity
Radiation or chemicals
Spontaneous errors during DNA replication
133
What could radiation or chemicals lead to?
DNA mutations
134
How does a tumour form?
Uncontrolled mitosis causes cancerous cells to divide repeatedly
135
What does uncontrolled mitosis casing cancerous cell to divide repeatedly cause?
A tumour forms
136
Tumour
An irregular mass of cells which prevent the normal function of body organs
137
An irregular mass of cells which preen the normal function of body organs
Tumour
138
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
139
What type of cells don’t contain a centriole for forming spindles?
Plants cells
140
In what type of cells does the spindle degenerate and at which phase?
Animal cells at telophase
141
What happens to the spindle in plant cells?
Remains as the new wall is formed
142
What type of cells does cytokinesis occur in?
Animal cells
143
What forms between the 2 new nuclei in plant cells mitosis?
A cell plate which develops into a new cell wall
144
Where does meiosis occur?
In reproductive organs that produce gametes
145
What type of cell division occurs in reproductive organs that produce gametes?
Meiosis
146
How many chromosomes do gametes have?
1/2 the normal chromosome number (haploid number)
147
Haploid number (+give an example)
Half the normal chromosome number (e.g - gametes)
148
What do the cells produced during meiosis have?
Genetic variation
149
In what type of cell division do cells have genetic variation?
Meiosis
150
What does meiosis play an important role in?
Bringing out genetic variation in living organisms
151
What’s important for bringing out genetic variation in living organisms?
Meiosis
152
Diploid number formula
2n
153
2n formula
Diploid number
154
Haploid number formula
n
155
n formula
Haploid
156
How are gametes haploid cells?
They have 1 copy of each chromosome
157
How many chromosomes do humans have and in what form?
46 in 23 homologous pairs
158
What are the pairs that human chromosomes exist in?
Homologous pairs (23 of them)
159
What are human cells generally?
Diploid cells - contain 2 copies of each chromosome
160
What do gametes do at fertilisation and how does this affect haploid and diploid numbers?
Fuse, restoring the diploid number
161
When is the diploid number restored for gametes?
During fertilisation
162
What does gametes being haploid cells ensure?
Ensures that the chromosome number of individuals remains the same from generation to generation
163
Why is each cell genetically different following meiosis?
Crossing over
Random assortment
164
What does crossing over and random assortment cause in cells?
Causes them to be genetically different
165
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
166
What’s the whole first set of meiosis stages known as?
First meiotic division (meiosis I)
167
What is essentially occurring during meiosis I?
Separation of homologues
168
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
169
What forms a bivalent and during which stage of meiosis I?
During prophase I, chromosomes joining up in homologous pairs
170
How can we recognise bivalents in prophase I?
4 arms
171
What do 4 arms represent (meiosis)?
Bivalents, during prophase I
172
What does crossing-over lead to?
Genetic variation between generations
173
What type of process is crossing - over?
Random
174
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
175
What’s the name for the connections formed during the crossing over stage of prophase I?
Chiasmata
176
Chiasmata
The connections formed between homologous chromosome pairs during the crossing over stage of prophase I in meiosis
177
What occurs when chromosomes move closer together during the crossing over stage during prophase I?
Synapsis
178
What type of chromosomes exchange genetic information during crossing over?
Homologous chromosome pairs
179
Why does crossing over work?
Genes are in the same places on the chromosomes, but could be different alleles/versions of the gene
180
Allele
Version of a gene
181
Different versions of a gene
Alleles
182
What do chromosomes have different combinations of following crossing over?
Alleles
183
In what type of cells do centrioles migrate to the poles?
Animal cells
184
Which stage of prophase I occurs in animal cells alone?
Centrioles migrate to the poles
185
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)
186
How do bivalents attach to the spindle?
By the centromeres
187
Independent assortment
However bivalents arrange themselves along the equator of a cell (its random and independent of one another)
188
However bivalents arrange themselves along the equator of a cell (its random and independent of one another)
Independent assortment
189
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
190
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
191
What’s the possibility of 2 identical gametes in 2 people?
Practically zero
192
The possibility of 2 identical what in two people is practically zero?
2 identical gametes
193
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
194
During anaphase I, what are the chromosomes pulled away from and what stays together?
Chromosomes are pulled away from their bivalent
Chromatid stays together
195
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
196
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
197
What happens following cytokinesis in telophase I?
2 cells form, each with a haploid nucleus
198
What has happened to the number of chromosomes per cell following telophase I?
Halved
199
What’s the number of chromosomes before telophase I known as?
Diploid number
200
What’s the number of chromosomes following telophase I known as?
Haploid number
201
Why is the number of chromosomes in the new cells following telophase I half the original amount?
Chromosomes are no longer paired
202
Diploid number
Total chromosomes
203
Haploid number
1/2 total chromosomes
204
What’s the name for the second stage of meiosis?
Second division of meiosis (meiosis II)
205
What essentially occurs during the second division of meiosis?
Sister chromatids are separated (by mitosis)
206
Is there DNA replication between the two divisions of meiosis?
No
207
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
208
What is broken down during cytokinesis and in which stage of meiosis does it reform
The spindle
Reforms during prophase II
209
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
210
How can the chromatids move towards the pole and why?
Randomly, as they’re not identical in metaphase II
211
When does independent assortment occur in meiosis?
Metaphase I and II
212
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
213
How are chromatids pulled to the poles of the cells?
By contraction of the spindle
214
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
215
By which stage are haploid cells formed during meiosis?
Telophase II
216
Why do gametes have to be haploid cells?
When they join during fertilisation, we need to form a diploid cell to form the zygote
217
What is formed when gametes join and what is this process known as?
A zygote, during fertilisation
218
What type of cell is a zygote?
Diploid cell
219
Describe the gametes formed during telophase II of meiosis
Genetically varied
220
Why are gametes genetically varied?
Mixed chromosomes, which contain different combinations of alleles
221
Make 6 comparisons between mitosis and meiosis
(Check table in notes)
222
Compare division between mitosis and meiosis
Mitosis - 1 division resulting in 2 daughter cells
Meiosis - 2 divisions resulting in 4 daughter cells
223
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)
224
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)
225
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
226
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)
227
Compare the crossing over situation across mitosis and meiosis
Mitosis - no crossing over
Meiosis - crossing over occurs and chiasmata form
228
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
229
Where does meiosis occur in animals?
In the testes (sperm) or the ovaries (egg)
230
Where does meiosis occur in plants?
In the anther (pollen formation) or the ovule (egg cell)
231
Why is the protein synthesis stage of interphase important?
for the formation of a spindle from protein microtubules
232
Define a diploid
an organism with 2 complete sets of chromosomes
233
An organism with 2 complete sets of chromosomes
Diploid
234
Homologous chromosomes
the same size and shape and carry the same genes, but may be different alleles
235
the same size and shape and carry the same genes, but may be different alleles
Homologous chromosomes
236
What’s the only difference in homologous chromosomes?
different alleles
237
What happens during cytokinesis?
the cytoplasm divides
238
when does a cytoplasm divide?
during cytokinesis
239
Polyploidy
where an organism has more than two complete sets of chromosomes
240
where an organism has more than two complete sets of chromosomes
polyploidy
241
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)
242
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
243
What does using a stain in an experiment do?
Stain the DNA
244
What makes DNA easier to see in an experiment?
Staining
245
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
246
What do we NOT say during the period in which a cell increases in size during interphase?
That it’s grown
247
What’s DNA present as following interphase?
Chromosomes
248
Synapsis
Fusion of chromosome pairs at the start of meiosis
249
Fusion of chromosome pairs at the start of meiosis
Synapsis
250
When does Synapsis occur?
At the start of meiosis
251
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
252
What happens to the quantity of DNA following cytokinesis?
Halves
253
What does asexual reproduction produce and via what?
Clones, via mitosis
254
When does crossing over occur?
Prophase I
255
When does random assortment occur?
Metaphase I and II
256
What do photo encogenes do?
Act as a brake on cell division
If mutated, there’s no brake, so we get uncontrolled cell division
257
What act as a break on cell division?
Photo encogenes
258
The cell cycle
Cellular events that repeat in order between 1 cell division and the next
259
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
