S2) Mitosis and Meiosis Flashcards
Identify all the stages in the cell cycle
- G1
- S Phase
- G2 Phase
- M Phase
Describe what happens the G1 phase and when it begins
- Begins immediately after mitosis
- Synthesis of RNA, proteins, and organelles
Describe what occurs in the S Phase
DNA replication occurs, i.e. chromosomes form sister chromatids
Describe what occurs in the G2 Phase
- Mitochondria divide
- Synthesis of precursors of spindle fibres
Identify all the stages of M Phase (mitosis)
- Prophase
- Prometaphase
- Metaphase
- Anaphase
- Telophase
What occurs in prophase?
- Chromatin condenses due to supercoiling and chromosomes become visible
- Nucleoli disappear
- Nuclear envelope breaks down
- Centrioles divide and migrate to opposite poles
What occurs in prometaphase?
- Microtubules produce spindle fibres form
- Spindle fibres attach to centromere of chromosomes
What occurs in metaphase?
Chromosomes, with spindle fibres attached, line up on the equator of the dividing cell
What occurs in anaphase?
- Centromeres divide, converting each sister chromatid into a chromosome
- Chromosomes migrate toward opposite ends of the cell until there is a complete set of chromosomes at each end of the cell
What occurs in telophase?
- Chromosomes reach the opposite poles of the cell
- Chromatin decondenses & spindle fibres break down
- Nuclear membrane reforms
- Nucleoli reappear
What occurs in cytokinesis?
- Cleavage furrow forms at equator of cell and deepens
- Cytoplasm divides
- New nuclear envelope forms
Describe the structure of chromosomes
- Each chromatid consist of one identical DNA molecule
- Each chromatid has a p (short) and q (long) arm
- Telomeres at the end of each chromatid
- Centromeres link sister chromatids
Identify the different types of chromosome structures
What occurs in meiosis?
- Members of a chromosome pair separate from each other
- Each daughter cell receives a haploid (n) set of 23 chromosomes
- These haploid cells form gametes (sperm and egg)
Explain the reduction that occurs in meiosis
- Before cells enter meiosis, the chromosomes replicate during interphase
- Meiosis I reduces the chromosome number accomplished by two rounds of division (meiosis I and meiosis II)
How does fertilisation affect the overall chromosome number?
- Fusion of two haploid gametes in fertilisation restores the chromosome number to the diploid number of 46
- Fertilised egg has a full set of genetic information
Explain what is meant by the following terms:
- Homologous chromosomes
- Sister chromatids
- Non-sister chromatids
- Homologous chromosomes have the identical DNA but may have different alleles
- Sister chromatids have identical DNA and the same alleles
- Non-sister chromatids have identical DNA, but may have different alleles
How does recombination occur in meiosis I?
Meiosis produces new combinations of parental genes in two ways:
- Random assortment which puts random combinations of maternal and paternal chromosomes into gametes
- Crossing over which is the exchange of chromosome segments between non-sister chromatids of homologous chromosomes
What occurs in prophase I of meiosis?
- Chromatin condenses & chromosomes are visible
- Homologous chromosomes pair & crossing over occurs
- Newly forming spindle microtubules become attached to each chromosome
What occurs in metaphase I of meiosis?
- Paired chromosomes align at equator of cell
- Random assortment of chromosomes occurs
What occurs in anaphase I of meiosis?
- Paired homologous chromosomes separate
- Sister chromatids move to opposite poles
What occurs in telophase I of meiosis?
- Chromosomes uncoil
- Spindle fibres break down
- Nucleoli & nuclear envelop reform
What occurs in cytokinesis of meiosis I?
- Cytoplasm divides
- 2 haploid daughter cells are formed
- All chromosomes are still in the duplicated state
Outline Meiosis II
- Prophase II: Chromosomes re-coil and shorten
- Metaphase II: Unpaired chromosomes become aligned at equator of cell
- Anaphase II: Centromeres separate. Daughter chromosomes, which were sister chromatids, pull apart
- Telophase II: Chromosomes uncoil and nuclear envelope re-forms
- Cytokinesis: Cytoplasm divides forming 4 haploid daughter cells
What is spermatogenesis?
Spermatogenesis is the production of sperm which occurs in the testes of males
Outline the process of spermatogenesis
What is oogenesis?
Oogenesis is the production of gametes (ova) which occurs in the ovaries of females
Outline the process of oogenesis
Describe the phenomena of missegregation in meiosis
- 30% of human meiosis is faulty
- Consequences: miscarriages and infertility
How can chromosomes be analysed?
Metaphase spread:
- Stained metaphase chromosomes
- Actively dividing cells are needed
State the standard format used to describe the karyotype
Karyotype = Chromosome number, sex complement, structural changes (no spaces)
- E.g. 46,XX - normal female*
- E.g. 47,XY,+21 - male with trisomy 21*
What is mitotic non-disjunction?
Mitotic nondisjunction is when daughter cells have abnormal chromosome numbers (aneuploidy) due to the failure of sister chromatids separating in anaphase of mitosis
Aneuploidy can result fron non-disjunction.
Define this term
Aneuploidy is the presence of an abnormal number of chromosomes in a cell
What is mosaicism?
- Mosaicism is the presence of 2/more cell lines in an individual
- It can occur throughout the body or be tissue limited
- Non-disjunction can cause mosaicism
What influences the degree of mosaicism?
- When the first post-zygotic division occurs
- When later mitotic divisions occur
What is the role of the mitotic spindle in mitosis?
The mitotic spindle ensures the accuracy of chromosome segregation
The mitotic spindle is a proven target for successful cancer treatment.
Explain how
- Cancer cells are aneuploid (not diploid) and exhibit chromosome instability
- Treatments interfere with microtubules, preventing cell division in rapidly-dividing cancer cells
Cancer cells often display numerical chromosome instability (CIN).
What causes this?
- Mitotic errors promote CIN and tumour heterogeneity
- Amplified centrosomes, often seen in cancer, produce multipolar spindles which also promote CIN
What regulates spindle polarity?
Spindle polarity is regulated by centrosome number
What is the role of TSG?
Tumour suppresor genes (TSG) stop cancer growth
What is the role of oncogenes?
Oncogenes promote cancer growth
What results from TSG and oncogene mutations?
Centrosome amplification results from TSG and oncogene mutation
What is centrosome clustering and what does it do?
- Cancer cells have mechanisms to cluster amplified centrosomes
- Clustering extra centrosomes allows cancer cells to survive
Identify a therapeutic strategy targeting centrosome clustering
Inhibition of centrosome clustering to lead to cancer cell death
