2.2 Cell division and mutation Flashcards
What is the cell cycle
The sequence of events (dividing and non-dividing) stages in the life of a cycle
What are the 3 stages in the cell cycle
- Interphase
- Nuclear division
- Cytokinesis
What is a chromosome
Condensed chromatin which has coiled
What is chromatin
Double helix of DNA that has wrapped around histone proteins
What is present in diploid cells but not in haploid cells
Homologous pairs
What is the common name for somatic cells
Body cells
What is mitosis
Nuclear division in eukaryotic cells
When a cell undergos mitosis, what is produced
2 GENETICALLY identical daughter cells
What stays the same in mitosis
The number of chromosomes
What are the 6 stages of cell division, mitosis
- Interphase
- Prophase
- Metaphase
- Anaphase
- Telophase
- Cytokinesis
In what phase of mitosis, does cell growth occur
Interphase
In what stage of mitosis, are the chromosomes not visible
Interphase
In what stage of mitosis, are organelles synthesised
Interphase
In what stage of mitosis, is ATP synthesised
Interphase
In what stage of mitosis, does DNA replication occur
Interphase
In what stage of mitosis, do the centrioles move to opposite poles of the cell
Prophase
In what stage of mitosis, do the chromosomes condense and become visible as 2 sister chromatids joined by a centromere
Prophase
In what stage of mitosis, do spindle fibres develop from each pair of centrioles to span the cell from pole to pole
Prophase
In what stage of mitosis, do the chromosomes attach to spindle fibres by their centromere
Prophase
In what stage of mitosis, does the nucleolus disappear
Prophase
In what stage of mitosis, does the nuclear envelope break down so chromosomes are free in the cytoplasm
Prophase
In what phase of mitosis, are chromosomes pulled along the spindle apparatus and arrange themselves across the equator of the cell
Metaphase
In what phase of mitosis, do the centromeres divide in 2
Metaphase
In what stage of mitosis, do the spindle fibres contract and shorten pulling sister chromatids apart
Anaphase
In what stage of mitosis, do mitochondria located around the spindle fibres provide ATP for their contraction
Anaphase
In what stage of mitosis, are the chromosomes pulled to opposite poles
Anaphase
In what stage of mitosis, do chromosomes reach their respective poles
Telophase
In what stage of mitosis, does the nuclear envelope and nucleoli reform
Telophase
In what stage of mitosis, do the spindle fibres disintegrate
Telophase
In what phase of mitosis, do the chromosomes elongate becoming less visible
Telophase
In what phase of mitosis, does the cell membrane pinch inwards separating cytoplasm
Cytokinesis
In what phase of mitosis, does the cytoplasm divide to produce 2 new cells
Cytokinesis
What are the 3 mains importance of mitosis
- Growth
- Tissue repair
- Asexual reproduction
When looking at a diagram, how do you tell the difference between interphase and prophase of the cell cycle
The majority of the cells will be in interphase so whatever cell is shown more is in interphase
What is an advantage of having offspring that are genetically identical to their parents
In stable/ unchanged environments successful parents can rapidly produce successful offspring
What is a disadvantage of having offspring that are genetically identical to their parents
More vulnerable to changing environments because there is no genetic diversity
What is the mitotic index
The ratio of the number of cells undergoing mitosis to the total number of cells
During the root tip squash experiment, why do we use the root tip
It’s the growing region- where mitosis happens
During the root tip squash experiment, why is the acetic orcein stain necessary
To make the DNA visible- therefore making the chromosomes visible to view mitosis activity
During the root tip squash experiment, the HCl softens the walls, why is this necessary
So stain can enter the cells
During the root tip squash experiment, why is the hot plate a necessary
Speeds up the softening of the wall and speeds up the movement of the stain
During the root tip squash experiment, why is squashing the root tip necessary
It flattens the tip to make it a single layer of cells in order to view them on a microscope
During binary fission, once the circular DNA has replicated what do both copies attach to
The cell membrane
Do plasmids replicate
Yes
What is formed from binary fission
2 identical daughter cells, each with a single copy of circular DNA and a variable number of plasmids
What allows viruses to attach to host cells
Attachment proteins
Once a virus have attached to the host cell, what do they inject into the cell
Their nucleic acid
What does the host cell read from the injected viral nucleic acid
The genetic code
After the host cell has read the genetic code from the viral nucleic acid, what does the host cell begin to do
Produce viral components: nucleic acids, enzymes, structural proteins
After the viral components have been produced by the host cell, what does these components do
Assemble into new viruses
What does apoptosis mean
Controlled cell death
When does apoptosis occur
When a cell mutates, it then dies to stop the replication of a mutated cell
What are the 2 factors that control cell division in healthy cells
- Majority of differentiated cell don’t divide
- Apoptosis (controlled cell death)
What causes cancer in terms of cells
Result of uncontrolled mitosis
When do the chromosomes condense
During prophase
What happens in anaphase
Chromatids are pulled apart
What does the phrase reduction division refer too
Meiosis
What happens to the number of chromosomes during meiosis
They halve
How many consecutive divisions are there in meiosis
2
After interphase during meiosis, what is separated in the first division
Separation of bivalents
During meiosis, what are the products from the first division
2 haploid daughter cells
In the 2nd division stage of meiosis, what is separated
Separation of sister chromatids
What is produced from the 2nd division on meiosis
4 haploid daughter cells
During meiosis I, what is the behaviour of the chromosomes during prophase, and how does this differ from prophase of mitosis
Chromosomes condense and become visible, arranged as bivalent.
Whereas mitosis, the chromosomes only become visible and not arranged as replicated homologous pairs (bivalent)
During prophase of meiosis I, the chromosomes are visibly arranged as bivalent, what may this lead to
Crossing over
During metaphase of meiosis I, what is the behaviour of the chromosomes
Bivalents align at equator of spindles
During anaphase of meiosis I, what are separated, and how is this different from mitosis
Bivalents are separated
Whereas in mitosis it’s the sister chromatids
Is the chromosome behaviour for meiosis II, the same as mitotic behaviour or meiosis I behaviour
Mitotic behaviour
What is the comparative statement, mitosis produces 2 daughter cells whereas
Meiosis produces 4 daughter cells
What is the comparative statement, mitosis involves 1 cell division whereas
Meiosis involves 2 consecutive cell divisions
What is the comparative statement, mitosis produces somatic cells whereas
Meiosis produces gametes
What is the comparative statement, mitosis produces diploid daughter cells whereas
Meiosis produces haploid daughter cells
What is the comparative statement, the number of chromosomes during mitosis remains the same whereas
During meiosis the number of chromosomes is halved
What is the comparative statement, mitosis produces genetically identical daughter cells whereas
Meiosis produces genetically unique daughter cells
What is the comparative statement, mitosis is used for growth and repair whereas
Meiosis is used for sexual reproduction
What are the 2 significances of meiosis
- Produces haploid gametes
- Produces genetic variation
What are the 3 ways in which meiosis produces genetic variation
- Random fertilisation
- Independent segregation
- Crossing over
How does the random fusion of gametes (random fertilisation) allow for genetic variation
- Each parent is genetically different
- Each parent produces thousands of genetically unique gametes
- At fertilisation, the zygote has unique combination of alleles
What happens to the chromosomes when they condense so that they become shorter and fatter
They coil and super coil
Why does crossing over occur during prophase I
Since the chromosomes are visible and arranged as bivalents, and when they condense they super coil and due to them being close together the 2 chromosomes in each homologous pair can get tangled
What is the name of the product when non-sister chromatids in a bivalent cross over
Chiasma
When does crossing over during meiosis matter
When the alleles are different in the bivalent- if the alleles are the same then swapping of genetic information would not matter
When crossing over occurs during meiosis, what is the name of the chromosomes produced when the chromosomes have a different combination of alleles that isn’t present in either parent
Recombinant chromosomes
What are 2 other names for independent segregation
- Independent assortment
- Random assortment
What is the equation for the number of possible chromosome combinations - independent segregation topic
2 ^ (number of pairs present)
e.g. if there were 3 pairs in a cell then it would be 8= 2^3
Describe the term recombinant
A cell/ organism whose genetic material was produced when segments of DNA from different sources are joined
Describe the term independent assortment
The random alignment of bivalents in metaphase I
Describe the term homologous pairs
2 chromosomes with the same gene loci
Describe the term non-disjunction
The failure of homologous pairs to separate in meiosis
Describe the term crossing over
Chromatids within a pair become twisted around one another when condensing in prophase I
Describe the term bivalent
A pair of chromosomes with the same gene loci after DNA replication has occurred
Describe the term haploid
A cell/ organism containing a single set of chromosomes
Name the term that increase the chance of a mutation
Mutagenic agent
What causes a mutation
Nothing they are SPONTANEOUS and RANDOM
Why are mutation good
They provide genetic variation which is important so at least one individual can survive a change ins the environment
Are most mutation recessive
Yes
How common are beneficial mutations
Rare
What are the 2 types of mutations
- Point mutation
- Chromosome mutation
What is a point mutation
A change in the DNA base sequence
Why does a point mutation effect the organism - protein structure
It alters the amino acid sequence which alters the primary structure - altering the tertiary structure which can change the function or stop it from functioning at all
During which part of the cell cycle do point mutations occur
In interphase during DNA replication
What is a chromosome mutation
A change in the number of chromosomes
When do chromosome mutation occur during the cell cycle
During anaphase in meiosis
What is a substitution mutation
A base is substituted with another one
If a base is substituted with another base but they both code for the same amino acid, what is the name of the mutation
- A silent mutation
OR - A mutual mutation
What is and insertion mutation
Adding in extra bases
What is a frameshift mutation
When every codon downstream of the mutation will change, potentially every amino acid downstream - so potentially a great effect on the primary structure of the protein
What is a deletion mutation
Deleting bases
What is a duplication mutation
Adding in an extra base that is the same base as the one that came before
e.g. adding T after a T
What is an inversion mutation
When the bases become separated from the DNA and rejoin the same place but with a different order
What is a translocation mutation
A group of base gets separated from the DNA sequence from a chromosome and gets inserted in the DNA sequnce in another chromosome
What are the 3 types of point mutation, where a frameshift occurs
- Insertion
- Deletion
- Duplication
What are the 2 possible results from a chromosome mutation
- Polysomy
- Polyploidy
When does polysomy occur - after chromosome mutation
It occurs when one homologous pair fails to separate in a process known as non-disjunction
When does polyploidy occur- after chromosome mutation
When all homologous pairs fail to separate so all end up in the gametes - this is unique to plants
What phase in the cell cycle do chromosome mutation occurs
In anaphase during meiosis
When non-disjunction occurs in gene 21, how many sets of chromosomes are in the final cell
3 - its triploid
What is the proper name of the triploid chromosome 21 cell called - when the organism has down’s syndrome
Trisomy 21
When a non-disjunction cell separates, what happens to the zygote where there are no chromosomes in one of the gametes
Death
Monosomy 21
What are the 3 categories of mutagens
- Physical
- Biological
- Chemical
Name an example of a physical mutagen
Ionising radiation alpha and beta particles
Name an example of a biological mutagen
Viruses
Name an example of a chemical mutagen
Benzopyrene in tobacco smoke
Define the term mutagenic mutations
A factor that increases the rate of mutations
Why does random fusion of gametes increase genetic variation
Since there’s a new allele combination
Define gene mutation
Change in the base/ nucleotide sequence of chromosomes/ DNA
&
results in the formation of new alleles
Explain how a gene mutation can have no effect on an individual
Genetic code is degenerate
Does change amino acid but no effect on tertiary structure
Explain how a gene mutation can have a positive effect on an individual
- Results in change in polypeptide that positively changes the properties
- May result in increased survival
Explain how the chromosome number is halved during meiosis (2 marks)
- Homologous chromosomes
- One of each pair goes to each daughter cell
Describe the process of crossing over and explain how it increases genetic diversity ( 4 marks)
- Homologous pairs of chromosomes form a bivalent
- Chiasmata forms
- Equal length non-sister chromatids are exchanged
- Producing new combination of alleles
Explain why all body cells will experience the mutation if the mutation is in an egg cell (2 marks)
- Mutation chromosome in gamete
- All cells derived from zygote by mitosis
- Mitosis produces genetically identical cells
Describe the appearance and behaviour of chromosomes during prophase and during anaphase of mitosis (4 marks)
In prophase
- Chromosomes continue to condense
- Chromosomes are visible
- Chromosomes attach to spindle fibres
In anaphase
- Centromeres divide
- Chromosomes pulled to opposite poles
Does the replication of linear DNA involve mitosis or binary fission or both
Mitosis
Does the replication of circular DNA involve mitosis, binary fission, or both
Binary fission
Describe the role of spindle fibres and the behaviour of chromosomes during prophase, metaphase and anaphase (4 marks)
- (In) prophase, chromosomes condense;
- (In) prophase OR metaphase, centromeres
attach to spindle fibres; - (In) metaphase, chromosomes/pairs of
chromatids at equator/centre of spindle/cell; - (In) anaphase, centromeres divide;
- (In) anaphase, chromatids (from each pair)
pulled to (opposite) poles/ends (of cell); - (In) prophase/metaphase/anaphase, spindle
fibres shorten;
Define non-coding base sequences (1 mark)
- DNA that does not code for protein/polypeptides
OR
DNA that does not code for (sequences of)
amino acids
OR
DNA that does not code for tRNA/rRNA;
Describe where non-coding multiple repeats are positioned in the genome (1 marks)
Positioned between genes;
Describe how bacteria divide (2 marks)
- Binary fission;
- Replication of (circular) DNA;
- Division of cytoplasm to produce 2 daughter
cells; - Each with single copy of (circular) DNA;
