Cell Division Flashcards
What happen during interphase?
Main : Replication of DNA Side: - Cell builds up a large store of energy - Cell Manufacture proteins - Cell synthesizes organelles
What happen during mitotic prophase / meiosis prophase II
Chromatin condenses to form chromosomes (nucleolus disappear)
Nuclear envelope breaks down
Centrioles move to opposite ends of the cell
Mircrotubules/Spindle fibres attach to centromerre of chromosomes and move them towards centre of cell
What happen during mitotic metaphase / meiosis metaphase II?
Chromosomes line up at spindle equator
What happen during mitotic anaphase/ meiosis II anaphase?
Sister chromatids of each chromosome are pulled apart by spindle fibre shortening
separated sister chromatids of each chromosomes move to opposite poles of spindle
What happen during mitotic telophase/ meiosis telophase II
- Nucleolus reappears
- Nuclear envelope reforms to form 2 daughter nuclei
- Chromosomes uncoil to form long and thin chromatin threads
- Spindle fibers disintegrate
What happen during cytokinesis?
In animals, a cleavage furrow forms and pinches cell into two, producing two daughter cells
In plants, a cell plate forms, growing outwards until it touches parental walls forming two separate cells
What are homologous chromosomes?
Any two chromosomes that determine same characteristics
All individuals of same species have same ___ and ____ of chromsomes
number
type
Do homologous chromosomes need to be identical?
No, they can contain different allele for same gene
Why is mitosis important
It is to produce genetically identical cells for:
- Growth of an organism (by increasing no. of cells)
- Repair of worn- out parts of tissue, replacing dead/damaged cells
- Asexual repro
Why must DNA replication and mitosis be precisely controlled?
– To ensure all daughters
cells are genetically stable
- If an error occur during replication, new DNA strand formed would be different from original (gene mutation)
- gene mutation passed on to daughter cell
- as genes are responsible for normal cell growth and division, some forms of gene mutation may lead to uncontrolled division of cells-cancer
Causes of cancer (5)
Age
Chemicals - carcinogen chemicals (ef tar in cigerrate smoke)
Radiation
Viruses
Genetic Factor - eg breast cancer runs in family
Importance of producing haploid gametes during meiosis during sexual repro
Produce haploid gametes which fuse tgt during fertilisation to produce diploid cells
This ensures number of chromosomes in an organism is maintained through successive generation
What happen during meiosis 1 prophase
- Chromatin thread condenses to form distinct chromosomes
- nucleolus disappears
- nuclear envelope disintegrate
- centrioles move to opposite ends of cells and short microtubules develop from them to form meiotic spindle
- Synapsis occur, homologous chromosomes pair up, forming bibalent
- crossing over between chromatids of homologous chromosome occurs at chiasma
What happen during meiosis 1 metaphase
- Bivalents arrange themselves at equator of spindle, aided by spindle fibers
- arrangement of chromosomes of each bivalent at spindle equator is completely independent of the orientation of other bivalents, resulting in indepenedent assortment of chromosomes
What happen during meiosis 1 anaphase
Spindle fibers shorten and pull one of each pair of homologous chromosomes to opposite pole of the cell
Difference between mitosis and meiosis I (3 diff)
MT: Single chromosomes arranged at equator
ME: Bivalents arranged at equator, held together by chiasma
MT: Microtubules from both poles attach to either one side of centromere
ME: Microtubules from one pole attached to one side of centromere
MT: Microtubules pull sister chromatids apart
ME: Microtubules pull homo chromosomes apart, sister chromatids remain intact
What happen during meiosis 1 telophase
Chromosomes reach opposite poles
Spindle fibers disintegrates
In animal cells, nuclear envelope and nucleolus reforms and cytokinesis occurs to form two haploid (n) daughter cells
Most plant cells do not undergo Telophase I and proceed to Metaphase II
Importance of Meiosis in Sexual repro
Meiosis results in genetic variation
- essential for evolution
- genetical variation allows naturals election to occur and individuals best adapted to surroundings to survive and reproduce offspring
- this allows species to change constantly and adapt when environment changes
How does crossing over at prophase I contribute to genetic cariation?
Formation of chiasma lead to crossing over of segments between non sister chromatids of homo chromosomes leads to new combi of alleles on chromosomes of gametes
How do genetic variation occur besides crossing over at prophase (3 sources)
Independent arrangement and separation of homologous chromosomes during metaphase 1 and anaphase 1
Independent arrangement and separation of chromosomes during metaphase 2 and anaphase 2
Random fertilization - a zygote is formed from the random fusion of independently produced gametes
Difference between Mitosis and Meiosis
Type of cell and locn in body
Function
No of nuclear divisions and daughter cells
No. of chromosomes in daughter cells
Genetic Content of daughter cells
Synapsis and crossing over
Type of cell and locn in body
MT: Somatic Cells in all parts of body
ME: Germ cells in gonads
Function
MT: Growth, repair and asexual repro
ME: Produce gametes for sexual repro
No of nuclear divisions and daughter cells
MT: 1 nuclear division to produce 2 daughter cells
ME: 2 nuclear division to produce 4 daughter cells
No. of chromosomes in daughter cells
MT: Diploid; same as parent cell
ME: Haploid; Half the number of parent cell
Genetic Content of daughter cells
MT: Genetically similar to each other and parent cell
ME: Genetically dissimilar to parent cell and each other
Synapsis and crossing over
MT: Chiasmata never formed and crossing over does not occur during prophase
ME: Chiasmata form and crossing over occur during Prophase I
Why is there a need to produce genetically identical cells? (2points)
To ensure that all daughter cells are genetically stable
To prevent negative gene mutations that can lead to genetic disorder/cancer
