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
meoisis - how the process occurs
- cell divides twice
- PMAT occurs x2
first division
P1; chromosomes condense
chromosomes line up with homologous pairs - which means they contain the same genes in similar loci
chromosomes cross over - transfer genetic material - results in variety siblings have
M1; chromosomes are now in the Middle
DIFFERENT to mitosis; chromosomes are in PAIRS
A1; chromosomes pulled away by the spindle
T1; 2 newly formed nuclei
cytokinesis occurs
second division
-P1; not v exciting
M1; CHROMATIDS line up in the middle i.e. there are no pairs - single file line
A1; CHROMATIDS pulled away
T1; 2 more nuclei formed
total; 4
cytokinesis occurs
meoisis produces cells that are genetically different; HOW?
-CROSSING OVER OF CHROMOSOMES ;
during prophase once chromosomes have lined up in homologous pairs they cross over transferring genetic material
-INDEPENEDENT/SEPARATION OF CHROMOSOMES
basically, a gamete is formed from an egg & sperm it has 2 parents with different genes
thats why they produce genetically different cells
linkage of genes
- genes that are on the same chromosome are linked
- while independent assortment means genes are randomly distributed if genes are vv close to each other on the same chromosome - they are more likely to stay together.
differences between the sex chromosomes in males and females
X&Y CHROMOSOMES
Female ; 2 X Male; X & Y
Y chromosome; much smaller carries less genes
most genes on sex chromosomes are carried on X chromosome
thus because males only have one copy of this X chromosome - they will express the phenotype of the gene even if its recessive
males are more likely to show recessive phenotypes for genes that are sex linked
some facts about chromosome and chromatids
we count chromosomes by the no. of CENTROMERES
when a pair of chromosomes come along they have 4 STALKS but only 1 centromere
therefore even when they replicate
to start - 46 chromosomes
when they replicate there are still 46 chromosomes but 92 chromatids due to the 4 stalks
