cell division ! Flashcards
mitosis !
a type of nuclear division which results in the production of 2 daughter nuclei which are genetically identical to the parent
importance of mitosis !
growth of an organism : new cells produced
repair of worn out cells
- replace dead & worn out cells with new ones
- produce new cells to heal wounds
asexual reproduction for vegatative reproduction
mitosis - interphase !
cells :
- absorb nutrients
- build up protoplasm
- synthesis new organelles
- replicate DNA
chromatin threads replicate -> centrioles replicate & divide
dna replication !
chromatin thread : replicates to produce 2 identical chromatin threads + coil & shorten to become chromosomes
chromosome : consists of 2 identical DNA molecules (sister chromatids joined at centromere)
precise control of DNA replication & mitosis !
ensures that daughter cells are genetically stable
- during DNA replication : all information is copied -> ensures that daughter cells produced contain all DNA needed for subsequent cell division & differentiation
ensure embryo develops normally
- cells formed as zygote divides must be genetically stable
- if error : will be transmitted to daughter cells -> harmful changes to genes & affect how the cell functions
prevents uncontrolled division of cells -> cancer
- cells : lose ability to control division & their normal functions
prophase !
chromatin threads : condense, coil, shorten to form chromosomes (consists of 2 sister chromatids attached at centromere)
2 pairs of centrioles : move apart to opposite poles of cell -> nucleolus disappears
nucleur envelope : disappears
spindle fibres form, extending from one pole of cell to another
metaphase !
chromosomes : line up singly along equator of spindle
centromere of each chromosome : attached to a spindle fibre
anaphase !
each centromere splits
spindle fibres : shorten & pull sister chromatids apart to opposite poles of cell
sister chromatids separated -> daughter chromosomes
telophase !
spidle fibres : disintegrates
nuclear envelope : forms around each set of chromosomes at each pole of cell
nucleolus : forms inside each nucleus
chromosomes : uncoil & lengthen -> chromatin threads
cytokinesis !
division of cytoplasm
in animal cells : cleavage forms, deepen & eventually split cell into 2 identical daughter cells
meiosis !
a form of nuclear division such that the daughter nuclei produced contain half the number of chromosomes as the parent nucleus
-> results in 4 daughter nuclei (half the number of chromosomes as parent cell)
importance of meiosis !
produces haploid gametes
- ensures that normal diploid number of chromosomes is restored when the nucleus of female gamete fuses with the nucleus of male gamete during fertilisation
results in variations in gametes produced
- increases chances of survival of species in the environment
- crossing over between homologous chromosomes at prophase 1
- independent assortment of homologous chromosomes at metaphase 1
independent assortment !
1 chromosome from each pair can combine with either chromosomes of the other pair
prophase 1 !
chromatin threads : condense, coil, shorten to form chromosomes (consists of 2 sister chromatids attached at centromere)
synapsis occurs : homologous chromosomes pair along their whole length
crossing over occurs : chromatids of homologous chromosomes twist around & exchange parts with each other -> produces new combination of alleles along chromosome
centrioles : reach oppotite poles of cell
nuclear envelope & nucleolus : disappear
spindle fibres : form
metaphase 1 !
pairs of homologous chromosomes : arrange themselves along equator of cell
- 2 chromosomes at each pair : face opposite poles of cell
each chromosome : attached to a spindle fibre
anaphase 1 !
homologous chromosomes : separate & pulled to opposite poles of cells
telophase 1 !
spindle fibres : disintegrates
nuclear envelope : reforms around chromosomes of each pole
cytokinesis 1 !
centrioles : replicate
cytoplasm : cleaves to produce 2 haploid daughter cells
prophase 2 !
chromatin threads : condense, coil, shorten to form chromosomes (consists of 2 sister chromatids)
2 pairs of centrioles : move to opposite poles of cells
nuclear envelope : disintegrates
spindle fibres : forms
metaphase 2 !
chromosomes : line up singly along equator
centromere of each chromosome : attached to a spindle fibre
anaphase 2 !
centromeres : divide
spindle fibres : shorten & sister chromatids are pulled towards opposite poles & separate to form daughter chromosomes
telophase 2 !
spindle fibres : disintegrates
nuclear envelope : form around 2 daughter chromosomes at each pole
nucleolus : reforms
chromosomes : uncoil & lengthen -> chromatin threads
cytokinesis 2 !
cleavage of cytoplasm : results in 4 daughter cells each with haploid number of chromosomes produced
homologous chromosomes !
a pair of chromosomes of the same shape, genes & length
1 homologous chromosome from father, another from mother
mitosis vs meiosis - mitosis !
occurs in all cells
growth of organism & repair of tissue
involves 1 nuclear division -> 2 diploid daughter cells
daughter cells : genetically identical to parent cell & each other
homologous chromosomes : do not pair up
crossing over : does not occur
mitosis vs meiosis - meiosis !
occurs in only reproductive organs
produces gametes for sexual reproduction
involves 2 nuclear divisions -> 4 haploid daughter cells
daughter cells : have 1/2 the number of chromosomes as parent cell
genetic variation occurs in daughter cells
homologous chromosomes : pair at prophase 1
crossing over : may occur
variation in offspring !
genetic variation among daughter cells : produced due to crossing over of non-sister chromatids & independent assortment of chromosomes during meiosis
increases chances of survival of species during changes in envrionment
- variant genes : allow organism to better adapt to the changes in environment
random fertilisation !
involves a random sperm + a random egg released during ovulation
- produces further variation in offspring produced
