AQA A Level Biology - Topic 4 Genetics, Variation and Interdependance

mutation

any change in the DNA base sequence
creates a new allele

not always harmful as:
degenerate
passive allele
removed as intron
no effect on tertiary structure

components of DNA

deoxyribose
a phosphate group
nitrogen base (AT GC)

HISTONES in eurokaryotic

components of RNA

ribose
a phosphate group
nitrogen base (AU GC)

phosphodiester bonds

between nucleotides
condensation

gene

sequence of bases on a DNA
location of a gene is LOCUS

introns

non coding
pre-mRNA
gets removed after transcription (splicing)
multiple repeats

only eukaryotic

exons

coding base sequences for polypeptide sequences of amino acids

degenerate

64 triplets possible, but only 20 amino acids
some codons result the same

features of genetic code

non-overlapping
mutations may occur
start and stop codons

each gene is separated by non-coding

alleles

different versions of a gene

chromosomes

humans have 46
or 23 homologous pairs

mRNA

created during transcription
complementary to tRNA and DNA
codon

tRNA

clover shape
anti-codon

attaches to specific amino acid

transcription

HYDROGEN bonds broken
DNA HELICASE

TEMPLATE strand made

free NUCLEOTIDES do COMPLEMENTARY base pairing
PHOSPHODIESTER bonds made

using RNA polymerase
pre-mRNA made (spliced and leaves through pore)

translation

1. mRNA binds to ribosome
2. Two codons bind
3. tRNA with anticodons to bind
4. formation of peptide bonds
5. Moves along (mRNA to the next codon)

substitution

one nucleotide replaces another

insertion

randomly inserted
new base triplet, knock on effect (changes polypeptide sequence)
FRAMESHIFT

deletion

randomly deleted
FRAMESHIFT

nonsense (subst)

base change to STOP codon
stopped prematurely.
cannot function

mis-sense (subst)

different amino acid made
different polypeptide

silent (subst)

different base but same amino acid
no effect

chromosome mutation

changes in whole sets of individual chromosomes

inversion chromosome

reverses the direction

translocation chromosome

breaks occur
segments are exchanged

meiosis

genetically different
results in half no of chromosomes
haploid gametes made

independent assortment (chromosomes)

homologous pairs orient randomly at metaphase I

meiosis 1

homologous chromosomes pair up
crossing over at the chiasmata
each daughter cell contains one chromosome from each homologous pair

meiosis 2

chromatids separate
2 chromatids each in 4 haploid cells

genetic diversity

total number of different alleles in the population
genetic variation

niche (of a specie)

role within the environment

natural selection

process in which individuals better adapted to the environment survive
pass on the advantageous genes

evolution

frequency of alleles in a gene pool changes as a result of natural selection

environmental CHANGE needed for selection PRESSURE

directional selection

environmental conditions CHANGE
moving towards direction of fitter individuals

eg. antibiotic resistant bacteria

Stabilising selection

environment stays the same
diversity reduced
individuals closest to the mean

niche

specie role within the environment

environmental adaptation

Anatomical, behavioural, physiological

courtship behaviour

Recognise members of own species
Synchronise mating and attracts males
Form a pair bond
Become able to breed

KPCOFGS

classification

domain

above the kingdom level
Archaea, Bacteria, Eukarya

biodiversity

variety of living organisms

Species diversity

number of:
different species
number of different individuals
- in a community

index of diversity

number of:
species present in a community
abundance of each species

impacts of agriculture

Using hedgerows instead of fences
intercropping
Reducing the use of herbicides and pesticides
Preserving wetlands

comparing genetics

observable characteristics (limited)

DNA/mRNA sequencing
amino acid sequence
(gene technology)

sampling

random selection of individuals to measure representative of whole population

using quadrats or transects
(needs large sampling size + repeats)

genetic diversity in meiosis

crossing over and independent assortment

specie richness

the number of different species in a community

crossing over

homologous pairs associate
chiasma form
chromatids exchanged
new combinations of alleles

statistical significance

the smaller the number is, the more significant
if equal to a probability, not significant

genetic diversity comparison

order of:
DNA
mRNA
amino acid sequence

non-disjunction

failure homologous chromosomes to separate during meiosis