cell division & meiosis Flashcards
describe the features of Prophase
nuclear membrane begins to breakdown
centrioles move to poles of the cell
chromatin supercoils and condense in chromosomes
describe the features of Metaphase
spidle fibres form
spindle fibres attach
to the centromere of chromosomes
chromosomes align at the equator
describe the features of Anaphase
spindle fibres shorten
centromere splits
sister chromatids are separated
chromatids pulled to opposite poles of the cell
describe the features of Telophase
nuclear membrane begins to reform
chromosomes unwind
what is a homologous pair of chromosomes ?
two chromosomes that carry the same genes in the same loci / location
describe and explain what the student should have done when counting cells to make sure that the mitotic index he obtained for this root tip was accurate
description; explanation;
- examine large number of fields of view / many cells
- to ensure representative sample
OR
- repeat count
- to ensure figures are correct
OR
- method to deal with part cells shown 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
- homologous chromosomes pair up
- maternal and paternal chromosomes are arranged in any order
- independent segregation
- crossing over
- (equal) Portions of chromatids are swapped between chromosomes
- produces new combination of alleles
- chromatids separated at meiosis II/ later
describe the process of crossing over and explain how it increases genetic diversity
- homologous pairs of chromosomes associate / form a bivalent
- chiasma(ta) form
- (equal) lengths of (non-sister) chromatids / alleles are exchanged
- producing new combinations of alleles
give two differences between mitosis and meiosis
mitosis given first
- one division, two divisions in meiosis
- (daughter) cells genetically identical, daughter cells genetically different in meiosis
- two cells produced, (usually) four cells produced in meiosis
- diploid to diploid/haploid to haploid, diploid to haploid in meiosis
- separation of homologous chromosomes only in meiosis
- crossing over only in meiosis
- independent segregation only in meiosis
describe binary fission in bacteria
- replication of (circular) DNA
- replication of plasmids
- division of cytoplasm (to produce daughter cells)
Formula to work out Mitotic Index?
(number of cells with condensed chromosomes/ total number of cells) × 100
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
Describe and explain the processes that occur during meiosis that increase genetic variation (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
Where does DNA replication occur
During the interphase of the cell cycle.
What is mitosis
The part of the cell cycle in which a eukaryotic cell divides to produce two daughter cells, each with the identical copies of DNA produced by the parent cell during DNA replication.
