Cell Cycle and Cell Division Flashcards
Describe the features of prophase (3)
- Nuclear membrane begins to breakdown
- Centrioles move to poles of the cell
- Chromosomes supercoil and condense and become visible
Describe the features of metaphase (3)
- Spindle fibres form and attach
- To centromere of chromosomes
- Chromosomes align at the equator of cell
Describe the features of anaphase (3)
- Spindle fibres shorten
- Centromere splits
- Sister chromatids are separated and pulled to opposite poles of the cell
Describe the features of telophase (2)
- Nuclear membrane begins to reform
- Chromosomes unwind and become thinner
Describe the appearance and behaviour of chromosomes during mitosis (5)
- During prophase, chromosomes supercoil and condense to become visible
- Chromosomes appear as 2 identical sister chromatids joined by a centromere
- During metaphase, chromosomes line up at the equator of the cell
- Chromosomes attach to spindle fibres
- By their centromere
- During anaphase, the centromere splits
- Sister chromatids are pulled to opposite poles of the cell making a V shape
- During telophase, chromatids uncoil/unwind and become thinner
Formula to work out Mitotic Index?
(number of cells with condensed chromosomes/total number of cells) x 100
What is a homologous pair of chromosomes? (1)
two chromosomes that carry the same genes in the same loci
Describe and explain what the student should have done when counting cells to make sure that the mitotic index he obtained for his root tip was accurate. (2)
- Examine large number of cells
- To ensure representative sample
OR - Repeat count
- To ensure figures are correct
OR - Method to deal with parts of cell showing at edge /count only whole cells
- To standardise counting
Meiosis results in cells that have the haploid number of chromosomes and show genetic variation. Explain how. (5)
- Homologous chromosomes pair up
- Maternal and paternal chromosomes are arranged in any order
- Independent segregation
- Crossing over
- Equal lengths of alleles are exchanged between chromosomes
- Produces new combination of alleles
- Chromatids separated at meiosis II
Describe the process of crossing over and explain how it increases genetic diversity (4)
- Homologous pairs of chromosomes form a bivalent
- Chiasmata form
- Equal lengths of alleles are exchanged
- Producing new combinations of alleles
Describe and explain the processes that occur during meiosis that increase genetic variation (5)
- Homologous chromosomes form a bivalent
- Independent segregation occurs
- Maternal and paternal chromosomes are reshuffled in any combination on the equator
- Crossing over leads to equal lengths of alleles being exchanged
- Creates new combination of alleles
Give two differences between mitosis and meiosis (2)
- Mitosis involves one division whereas meiosis involves two divisions
- Mitosis produces genetically identical daughter cells whereas meiosis produces genetically different daughter cells
- Mitosis produces 2 cells whereas meiosis produces 4 cells
- Mitosis involves diploid to diploid or haploid to haploid whereas meiosis involves diploid to haploid
- Separation of homologous chromosomes only in meiosis
- Crossing over only in meiosis
- Independent segregation only in meiosis
Describe binary fission in bacteria (3)
- Replication of (circular) DNA
- Replication of plasmids
- Division of cytoplasm (to produce daughter cells)
The events that take place during interphase and mitosis lead to the production of two genetically identical cells. Explain how. (4)
- DNA replicated
- Specific complementary base-pairing
- Two identical sister chromatids
- Each chromatid separated to opposite poles of cell.
