cell cycle

• Why is mitosis necessary?

  - needed for cell growth

  - repairing damaged organs

  - method of asexual reproduction in plants and fungi
• stages of mitosis

  prophase, metaphase, anaphase, telophase
• what happens during early prophase

  -chromosomes become more distinct- they coil up, shorten and thicken

  - centriole divides

  - nucleolus becomes more prominent
• what happens during late prophase

  - centrioles migrate to opposite poles

  - nuclear envelope disintegrates
• what happens during metaphase

  - each centriole is at a pole

  - centrioles grow spindle fibres which attach to the centromeres

  - chromosomes are pulled to the equator of the cell
• what happens during anaphase

  -spindle fibres shorten, causing chromatids to be pulled to opposite ends of the cell

  - centromere divides
• what happens during telophase

  - chromatids reach the poles of the cell and begin to uncoil

  - chromatids look less distinct

  - nuclear envelope starts to reform
• what is cytokinesis

  division of the cytoplasm
• Cytokenis in animal cells

  -cell membrane is pulled inwards by cytoskeleton

  - creates a groove which eventually deepens

  - eventually each membranes fuse to form 2 cells
• what can't plant cells divide

  have cell walls
• Cytokenis in plant cells

  - vesicles from the Golgi begin to assemble at the equator

  - vesicles fuse with each other and the cell surface membrane

  - new sections of cell wall then form along new sections of membrane
• what type of division is meiosis

  reduction division
• role of meiosis

  creates genetic variation during sexual reproduction

  - creates 4 haploid daughter cells
• stages of meiosis 1

  Prophase 1, Metaphase 1, Anaphase 1, Telophase 1
• what does meiosis 1 do

  introduces genetic diversity

  - results in 2 haploid cells
• what does meiosis 2 do

  separates sister chromatids

  - results in 4 haploid cells
• stages of meiosis 2

  prophase 2, metaphase 2, anaphase 2, telophase 2
• What are homologous chromosomes?


  Two genetically similar chromosomes, one from each parent- same gene different alleles
• how many chromosomes in a homologous pair

  46
• what is the position of a gene in a chromosome called

  locus of a gene
• what is the cell cycle

  series of events that cells go through as they grow and divide
• what are the 5 phases in the cell cycle

  G1, S, G2, mitosis, cytokinesis
• where are the 3 checkpoints in the cell cycle

  G1, G2, M
• what happens during interphase

  -G1, S, G2

  -cell replicates its DNA

  -cell is checked for errors

  - protein synthesis
• what happens during G1

  -organelles replicate

  - transcription and translation

  - cell size increases
• what happens during S phase

  DNA is replicated
• what happens during G2

  cell prepares for cell division: cell checked for errors, protein synthesis, translation and transcription
• what happens during G0

  cells move into or out of the cell cycle
• reasons for G0

  Differentiation or cell damage
• G0: Differentiation

  process in which cells become specialized in structure and function
• G0: DNA is damaged

  - cell division is no longer viable

  - enters a state of permanent cell arrest

  - most cells do this as they can only divide a set number of times
• what do the checkpoints check for

  cell is dividing properly and carrying out its function
• What is a bivalent?

  a pair of homologous chromosomes
• What is chromatin?

  uncoiled DNA
• what is a chromatid?

  one half of a duplicated chromosome
• What happens during prophase 1

  - chromosomes condense

  - nuclear envelope disintegrates

  - spindle fibres begin to form

  - homologous chromosomes pair up, forming bivalents

  - crossing over occurs as chromatids tangle together
• What is crossing over

  The homologous chromosomes twist around each other and bits of chromatids swap over. The chromatids still contain the same genes but now have a different combination of alleles
• What is the part of the chromatids that break and rejoin called

  Chiasmanta
• What are the chromosomes called after crossing over

  Recombinant Chromatids
• What happens during metaphase 1

  - homologous chromosomes form a lime on the equator ( independent assortment occurs)

  - spindle fibres attach to the centromeres