Year 12 - Cell division Flashcards
Describe the appearance and behaviour of chromosomes during mitosis
Prophase:
1. Chromosomes condense to become visible
2. Chromosomes appear as two identical sister chromatids joined at the centromere
Metaphase:
3. Chromosomes line up along the equator of the cell
4. Spindle fibres attatch to chromosomes at the centromere
Anaphase:
5. Spindle fibres shorten to split the centromere and sister chromatids are pulled to opposite poles of the cell making a V shape
Telophase:
6. Chromosomes uncoil and become thinner
Describe how the process of meiosis results in the haploid cells.
- DNA replicates
- There is two divisions.
- In the first division there is separation of homologous chromosomes
- In the second division there is separation of sister chromatids
- This produces 4 haploid cells
Describe the process of independent segregation and explain how it increases genetic diversity
- The Homologous chromosomes randomly pair up along the equator of the cell.
- Independent segregation leads to maternal and paternal chromosomes being re-shuffled to produce new combinations of maternal and paternal chromosomes
Describe the process of crossing over and explain how it increases genetic diversity
- The homologous chromosomes form a bivalent
- Chiasmata form between non-sister chromatids of homologous chromosomes
- Equal lengths of non-sister chromatids / alleles are exchanged.
- Producing new combinations of alleles.
Describe how the process of meiosis results in haploid cells
- DNA replication during late interphase (S phase)
- Two divisions
- First division involves the separation of homologous chromosomes
- Second division involves the separation of sister chromatids
- This produces 4 haploid cells
Contrast meiosis and mitosis
- One division in mitosis whereas two divisions in meiosis;
- (Daughter) cells genetically identical in mitosis whereas daughter cells genetically different in meiosis;
- Two cells produced in mitosis whereas (usually) four cells produced in meiosis;
- Diploid to diploid/haploid to haploid in mitosis whereas diploid to haploid in meiosis;
- Separation of sister chromatids in mitosis, whereas Separation of homologous chromosomes only in meiosis (in first division. ;
- Crossing over only in meiosis whereas not in mitosis;
- Independent segregation only in meiosis whereas not in mitosis
Describe the purpose of tumour suppressor genes
Tumour suppressor genes code for polypeptides that stop cell division.
Describe the purpose of proto-onca genes
Proto-oncogenes code for polypeptides that start cell division.
What is a tumour?
A mass of cells from uncontrolled mitosis
Describe the difference between benign and malignant tumours
Malignant = Cells have metastasised and can spread around the body
Whereas
Benign = cells can’t metastasise and will not spread to other parts of the body.
Describe binary fission in bacteria
- Replication of circular DNA;
- Replication of plasmids;
- Division of cytoplasm (to produce daughter cells);
