8. Cell Division. Flashcards
What is a homologous pair of chromosomes?
Carry same genes in same locus(locus is position gene is found in chromosome. They could contain different alleles of those genes (father/mother)
What are the processes of mitosis?
Prophase
Metaphase
Anaphase
Telophase.
What happens in mitosis prophase?
Chromosomes condense and become visible.
Nuclear membrane breaks down.
Centrioles move to poles of cell.
(Identify on pic when lines are visible but still in circular shape)
What happens in mitosis metaphase?
Chromosomes align at centre of cell.
Spindle fibres attach to centromere.
What happens in mitosis anaphase?
Chromosomes pulled to poles of cell.
Spindle fibres contract
Centromere breaks.
What happens in mitosis telophase?
Chromosomes uncoil and become thinner.
Cytokinesis (division of cytoplasm) starts to take place.
Produce 2 genetically identical daughter cells.
Why does mitosis take place?
Cell replacement, growth, tissue repair and asexual reproduction.
Why do cancerous cells spread and why do they use drugs that prevent spindle formation?
Undergo uncontrollable mitosis.
No spindle fibres so cant attach to centromere so cant undergo metaphase/anaphase.
Whats the process of binary fission and what organelles does it occur in?
Prokaryotic cells( bacteria) divide rapidly in a short time. Don’t have chromosomes/centrioles.
1) circular DNA and plasmids in bacteria replicate.
2) cell elongates from middle moving DNA loops to poles of cell
3) cytoplasm divides
4 ) cell wall divide form 2 genetically identical daughter cells.
How do viruses replicate ?
1) virus use attachment proteins to bind to complementary receptors on host cell
2) inject their genetical material into host cell.
3) host cell, ribosomes, golgi etc make viral proteins and viral proteins assemble.
4) virus then released from cell.
In HIV) attachment proteins assemble bind to receptors on helper T cells. RNA enters cell and reverse transcriptase convert RNA to DNA.
How do you prepare stained squashed cell to identify stages of mitosis? RP
Place garlic root tips (where most mitosis occur) in HCL to break down the cell walls to stain chromosomes. Leave for 15mins. Remove and cut a root tip off. Place on slide and stain. Use mounted needle to squash the tip to obtain a single layer of cells. Place cover slip on top and view using microscope.
How do you calculate mitotic index and how do you ensure its accurate?
Number of cells containing visible chromosomes/ total no.cells in field of view.
. Examine a large number if fields of view to ensure a representative sample.
. Repeat count to ensure fig is correct.
Why does meiosis occur, what does it produce and what causes them to be genetically varied?
Produce 4 genetically different haploid daughter cells from a single diploid parent cell. (Diploid to haploid)
For sexual reproduction.
Genetically varied due to crossing over of non sister chromatids and independent segregation of homologous chromosomes (change in combo resulting in different alleles.)
Whats the process of meiosis?
Meiosis 1:
P1: homologous chromosomes pair up and non sister chromatids cross over.
M1: homologous pairs line up on equator + independent segregation occurs.
A1: spindle fibres pull chromosomes to poles of cell.
T1: form 2 daughter cells.
Meiosis 2 is the same as mitosis to produce 4 haploid cells.
How do you calculate the number of different combinations of chromosomes following meiosis without crossing over?
2^n
n is number homologous chromosome pairs or haploid number.
How does fertilisation occur?
2 haploid gametes combine to restore diploid increasing genetic variation.
Whats non disjunction in fertilisation and how does mutations occur?
Mutations in no.chromosomes arise spontaneously by chromosome non disjunction during meiosis as homologous chromosomes don’t separate (division 1) or sister chromatids don’t separate (division 2).
Mutations in meiosis that produce gametes will found in all cells of any offspring of that gamete after fertilisation as all cells derived from diploid zygote by mitosis and mitosis produce genetically identical cells.
Whats the formula to calculate number of combos of chromosomes after random fertilisation of 2 gametes?
(2^n) ^2
n is haploid number
2 is number of gametes.
How is mitosis different from meiosis?
Mitosis:
- produce genetically identical cells- 1 nuclear division - 2 daughter cells produced - used in asexual reproduction- used for growth/replace/repair - no crossing over/independent segregation - sister chromatids seperate - chromosome number maintained (haploid to haploid or diploid to diploid. )
Meiosis:
- produce genetically different haploid variation - 2 nuclear divisions - 4 daughter cells produced- used in sexual reproduction- used produce gametes- crossing over/ independent segregation- 1 division homologous chromosomes separate and 2nd division sister chromatids separate - chromosome number halved (diploid to haploid)
