2.1.6 Cell division, cell diversity and cellular organisation Flashcards
What is the order of the cell cycle?
Interphase, mitotic stages, cytokinesis
What are the stages of interphase?
G1, S, G2
What happens in G1 phase of interphase?
-Organelles replicate
- Size of cell increases
What happens in S phase of interphase?
-DNA synthesis
- Chromosomes are replicated
What happens in G2 phase of interphase?
-Energy stored replaced
-Chromosomes repair
-Size of cell increases
What are the 4 mitotic stages?
Prophase, metaphase, anaphase, telophase
What happens in prophase during mitosis?
-Chromatin condenses into chromosomes
-The nuclear envelope breaks down
-The centrioles divide and move to opposite ends of the cell for the purpose of spindle formation
What happens in metaphase during mitosis?
-Chromosomes become attached to spindle fibres at their centromere
-Chromosomes are pulled along spindle fibres to the equator of the cell causing them to line up at the centre of the cell (metaphase plate)
What happens in anaphase during mitosis?
-Centromeres divide
-Chromatids on each chromosome are separated and pulled to opposite poles of the cell
What happens in telophase during mitosis?
-Nuclear envelope reforms
-Spindle is broken down and dissapears
-Chromosomes uncoil
What happens during cytokinesis?
-Parent and replicated organelles move to opposite sides of the cell
-Cytoplasm divides producing 2 daughter cells with identical genetic information
What is the purpose of meiosis?
To produce 4 sets of genetically different haploid cells
What happens in meiosis 1?
Homologous chromosomes are separated from each other
What happens in meiosis 2?
Sister chromatids from each chromosome are separated
What are the eight stages of meiosis?
prophase 1
metaphase 1
anaphase 1
telophase 1
prophase 2
metaphase 2
anaphase 2
telophase 2
What happens in prophase 1 during meiosis?
-Chromosomes condense
-Nuclear envelope breaks down
-Homologous chromosomes pair up forming bivalents
-Spindle fibres form centrioles
-Crossing over occurs which shuffles alleles
What is crossing over in meiosis?
Exchange of DNA between chromatids on homologous chromosomes
What happens during crossing over in meiosis?
-Homologous chromosomes line up and twist around each other
-Wrapping causes sections of chromatid to break off and can be swapped over to the homologous chromsome
What are 2 ways meiosis leads to genetic variation?
-Crossing over of chromatids
-Independent assortment of chromosomes
What happens in metaphase 1 during meiosis?
-Homologous pairs of chromosomes line up at equator through attatchment of spindle fibres to centromeres
-Within the homologous pair, the chromosomes are randomly organised on either side of the equator= independent assortment
What happens in anaphase 1 during meiosis?
-Separation of homologous chromosomes to opposite poles (centromeres are not divided)
-For this to happen the chiasmata between homologous chromosomes break
What happens in telophase 1 during meiosis?
-Reforming of nuclear envelope around haploid nuclei containing half the number of chromosomes
What happens in prophase 2 during meiosis?
-Chromosomes condense
-Nuclear envelope breaks down
-New spindle formation
-Chromatids on each chromosome are no longer identical
What happens in metaphase 2 during meiosis?
-Individual chromosomes line up at centre through attatchment of spindle fibres to centromeres
-Chromatids are randomly assorted on either side of the equator
