Cell Cycle And Division Flashcards
What hold two chromatids together?
Centromere
Gamete: what is the Ploidy level, number of sets of chromosomes and number of chromosomes?
For a human
Ploidy level: haploid
Sets of chromosomes: 1
Number of chromosomes: 23
Body cell: what is the Ploidy level, number of sets of chromosomes and number of chromosomes?
Ploidy level: diploid
Sets of chromosomes: 2
Number of chromosomes : 46
What are the three stages of the cell cycle?
Interphase
Mitosis
Cytokinesis
What are the three sub-stages of interphase
G1, s phase and G2
What happens in the phase G1?
Growth and normal metabolic processes
What happens in the S phase of interphase?
DNA replication.
What happens in the G2 stage of interphase?
Growth and preparation for mitosis by replication organelles
What is interphase?
A period of synthesis and growth
What is mitosis?
The formation of two genetically identical daughter nuclei.
What are the stages of mitosis?
PMAT Prophase Metaphase Anaphase Telophase
What is the final stage of the cell cycle
Cytokinesis where the cytoplasm splits to form two new daughter diploid cells.
Why does the total cell mass increase during the cell cycle and then decrease again?
Because during the s phase in interphase dna is replicated so mass increases then during cytokinesis the cytoplasm splits to it returns the two lots of the initial mass
Describe interphase
The longer stage of the cell cycle
Cell size increases
Chromosomes not yet visible
G1, s phase, G2
Describe prophase (mitosis)
The longest stage of mitosis
Chromosomes condense by coiling up and getting shorter and fatter
The centrioles(only in animal cells) divide and move to opposite poles of the cell
Centromere holds the sister chromatids together
Nuclear envelope disintergrates
Spindle forms
Describe metaphase (mitosis)
The chromosomes line up along the equator of the cell
Spindle fibres attach to the centromere and shorten slightly to pull the sister chromatids apart
Describe anaphase(mitosis)
The centromere divides into two, separating the sister chromatids as the spindle fibres Shorten.
Each sister chromatid reaches the opposite pole of the cell
Describe telophase (mitosis)
One chromatid from each chromosome has reached each pole
Chromosomes uncoil and lengthen returning to chromatin
The spindle breaks down and the nuclear envelope reforms
What are the significances of mitosis?
Growth
Asexual reproduction
Chromosome number
Damage and disease
What is the significance of growth in mitosis?
-new cells increase cell number in organism
-growth, repair tissue, replace dead cells
-new body cells made which are genetically identical
-some tissues are worn away all the time (skin and gut lining) replaced identically
Humans = bone marrow, hair follicles, nail cuticles
Plants= root, shoot , meristem
What is the significance of asexual reproduction with mitosis?
- genetically identical off spring to the parent
- occurs in: bacteria, yeast, greenfly, strawberry plants & plants with runners and bulbs and tubers
- no genetic variation between individuals so all identical
What is the significance of chromosome number in mitosis?
Daughter cells has same number as each other and parent
Each chromosome is an exact replica of those in parent
Cells produced are genetically identical to parent providing genetic stability
What is the significance of damage and disease in mitosis?
- genes control length of cell cycle so mitosis occurs when and where needed.
- if genes damaged incorrect divisions
- gene may mutate when: radiation chemicals viruses change dna base sequence
- gene will no longer act as a brake
- solid tissue=tumour forms// blood= blood cancer
What is an oncogene?
A gene with the potential to cause cancer
What is a tumour suppressing gene?
Genes that prevent rapid replication leading to tumour formation
What is a proto-oncogene?
A gene that causes cancer if it becomes mutated or a cell infected by a virus but before this they don’t cause cancer
Where does meiosis occur?
In reproductive organs
What is meiosis?
A two stage cell division in reproducing organisms that produces 4 genetically different haploid gametes with half the number of chromosomes than the parent
How many divisions are there in meiosis?
2
What are the stages in meiosis?
Interphase (G1, S, G2) Prophase I Metaphase I Anaphase I Telophase I + cytokinesis Prophase II Metaphase II Anaphase II telophase II + cytokinesis
Is there interphase between the two divisions in meiosis?
No
What is a terras also known as?
Bivalent
Describe prophase I
- Longest and most complex stage
- Chromosomes condense
- Synapsis= chromosomes from mum and dad pair up where homologous ones join together to form a bivalent
- Crossing over occurs and the chiasmata where part of one chromosome swaps with the other
What is crossing over?
When (during prophase I) part of the genetic material from the maternal and paternal chromosome swap. This occurs and the point called chiasmata
What is a bivalent?
A pair of chromosomes or 4 chromatids. One maternal and one paternal
Describe metaphase I
- shortest phase
- bivalent sapling either side of the equator
- spindle fibres attach to the centromere
- independent assortment of alignment of chromosomes along the equator.
What is independent assortment?
When the chromosomes and bivalent s arrange themselves randomly at the cell equator so genetic information can be passed one either way
What does independent assortment cause and why?
Variation because the orientation of the homologous chromosomes is random
Describe anaphase I
- homologous chromosomes separate and move to the poles of the cells
- sister chromatids stay attached to the centromere
Describe telophase I
Each pole now has a haploid set of chromosomes half the number of the chromosomes than the parent
Describe cytokinesis I
The daughter cells are haploid and formed by the cytoplasm splitting
Describe prophase II
The centrioles separate and move to the cell poles organising new spindle at right angles to the original spindle
Some nucleolus is present around the chromosomes
Describe metaphase II
Chromosomes line up along the equator where the spindle fibres attach to the centromeres
Independent assortment occurs as their orientation is random
Describe anaphase II
The centromeres divide in half so the sister chromatids move apart to either pole of the cell
To do this the spindle fibres shorten
Describe telophase II
At the poles the chromatids lengthen and can no longer be distinguishable through a microscope
The spindle disintergrates
Nuclear envelope reforms
Describe cytokinesis II
The cytoplasm splits from the inside outwards to form 4 haploid gametes
Why is meiosis significant?
The chromosome number is constant from one generation to the next
Genetic variation
How is genetic variation created during meiosis?
- prophase I= crossing over at the chiasmata where genetic information is swapped
- metaphase I &II = there is independent assortment of the chromosomes as the orientation is random
Why is it essential to have genetic variation?
When new diseases come, some people will be more resistant than others and some may adapt faster to new conditions.
What is a homologous pair?
Two chromosomes one maternal and one paternal which contain the same type of gene but may have different alleles.
