L5 & 6 A level leaning : variation in the genome, cell cycle , mitosis, meiosis Flashcards
Mitosis
Meiosis
Cell division that produces genetically identical cells
Cell division for sex cells
Uses of mitosis
- to repair damaged tissues
- ## asexual reproduction (1 parent only )
Cell cycle ;
During it what occurs??
Cell growth , DNA replication & mitosis
Cell cycle STAGES
G1, S, G2, M
G: gap phase
S: synthesis
M: mitosis
G1: cells grow, new proteins & organelles are made S: DNA replicated itself G2: cell continues to grow & proteins needed for cell division are made M: mitosis : -prophase - metaphase - anaphase - telophase
Interphase stage refers to ?
G1, S, G2
Mitosis : interphase then 4 stages
What happens at interphase ?
Interphase : cell carries out normal function but prepares to divide
- DNA unravels & ; replicates itself
- organelles = replicated
- ATP increases
Mitosis
Think DIAGRAMS
PROPHASE
- chromosomes have already replicated themselves in the interphase stage – becoming chromatids
- they get smaller &; fatter
- small proteins called centrioles migrate towards the poles — creating a SPINDLE (network of protein fibres) (3D)
- nuclear envelope around nucleus disappears
- chromosones are free to move in cytoplasm
METAPHASE
- chromosomes move toward middle - & are attached by centromere & spindle
ANAPHASE :
- centromere divides chromatids
- spindle contracts
- centromeres move towards poles (head first)
- chromosomes in a v shape
TELOPHASE :
- chromatids get longer &; thinner : become chromosomes at each pole
- nuclear envelope develops at each pole - 2 nuclei form
- cytoplasm divides : CYTOKINESIS
- 2 daughter cells genetically identical are produced
VARIATION
in phenotype
phenotype ; characteristics displayed by an organism
characteristics can be continuous i.e. no specific range e.g. height
or ; discontinuous meaning there are limits e.g. blood group - only 4 choices
genotype is to do with ;
the alleles a person has
these alleles have an impact on the phenotype
characteristics an organism displays depends on the genotype i.e. GENES
GENES control them in 2 ways ;
monogenic - controlled by only one gene - tends to show discontinuous variation
polygenic ; controlled by no. of genes in different loci (locations) -continuous variation
other way phenotypes can be influenced
environmental factors
e.g. height - potential to grow tall if its in your genes but if u are malnourished you won’t grow to your full potential
epigenetic code/control
SOME EXAMPLES
refers to a change in gene expression caused by adding or taking away chemical groups and
NOT BY ALTERING BASE SEQUENCE OF DNA
by adding or taking away them groups - alters how easy it is for enzymes & proteins to carry out transcription
e.g. adding methyl represses DNA as it prevents transcriptional factors binding thus transcription can’t occur
where would methyl groups bind in this case i.e. what SITE?
CpG site - between cytosine & guanine in base sequence of DNA
Modification to histone groups
counts as an ex for a change in gene expression w/o altering base sequence of DNA
- structure of histone groups
- process of changing gene expression
structure ; strings of DNA wrapped around histone proteins – creating CHROMATIN
Adding acetyl groups loosens bond between DNA & histone proteins
histone proteins loosen means they lose some of their positive charge & thus attraction to neg- DNA weakens
this allows TF to bind
taking away acetyl groups does opposite
meoisis
- WHAT is it?
- what happens to chromosomes ?
REDUCTION cell division that produces gametes
no. of chromosomes at end is halved
divides 2 diploid to 4 haploid cells
