cellular control, patterns of inheritance

mutations

changes in the sequence of nucleotides in DNA molecules

insertion / deletion mutations

one or more nucleotide pairs are inserted or deleted from sequence - frameshift mutation

substitution (point) mutation

one base pair is replaced by another

nonsense mutation

translation stopped early - truncated polypeptide

missense

codon change → production of different amino acid → altered tertiary structure of protein

silent

codon change which does not affect amino acid sequence → degenerate nature

mutation effects

beneficial / neutral / harmful

transcriptional control

lac operon :

conc. of glucose high, conc. of lactose low

transcription of structural genes inhibited by repressor protein binding to operator region

conc. of glucose low, conc. lactose high

lactose binds to repressor protein binding→ causes shape of DNA binding site to change, inefffective

cannot bind to operator region, therefore RNA polymerase can bind to promoter region, transcription takes place

transcription factors

have the ability to switch genes on/off, by interacting with promoter sequence of DNA to initiate / inhibit transcription

post transcriptional level

editing of primary mRNA where introns are removed, creating mature mRNA formed of exons

post translational level

adrenaline binds to complementary receptor, activates adenyl cyclase which converts ATP to cyclic AMP which starts a cascade of enzyme reactions within the cell

homeobox genes

controls body plan of organisms by coding for transcription factors which bind to DNA by switching genes on/off. they are arranged in hox clusters

apoptosis

programmed cell death which controls development of body plans. cells are broken down by enzymes and engulfed by phagocytes and destroyed

continuous variation

quantitative variation eg. height, weight

discontinuous

assigned to a particular category, eg. shoe size, blood type

meiosis genetic variation

crossing over : when pairs of homologous chromosomes line up and exchange some of their genetic material

independent assortment : various combinations of chromosome arrangement

allele

alternative forms of a gene

locus

position of a gene on a chromosome, 2 alleles are found at the same loci on chromosome pairs

genotype

alleles present within cells of an organism

dominant

only single allele required for expression in phenotype

recessive

only expressed if there is no dominant allele present

epistasis ratios

recessive : 9:3:4

dominant : 12:3:1

hardy weinberg principle

used to estimate frequency of alleles in population

p = frequency of dominant allele

q = frequency of recessive allele

p² =frequency of homozygous dominant

2pq = frequency of heterozygous

q²= frequency of homozygous recessive

niche of a species

role within environment

anatomical adaptations

physical adaptations eg. loop of henle

behavioural adaptations

changes in behaviour eg. mating calls

physiological adaptations

processes inside an organism’s body which increases change of survival

genetic drift

small change in allele frequency due to not all individuals in a population reproducing → amplified in very small groups

genetic bottleneck

rapid reduction in population size via some event (eg. natural disaster). has an effect on population size via and genetic variation in future generations

founder effect

decrease in genetic diversity which occurs when population descends from a small number of ancestors

speciation

new species arise after a population becomes separated and cannot interbreed

allopatric speciation

causes by a physical barrier, gene flow is reduced → frequency of alleles changes via natural selection→ can no longer interbreed, becomes separated species

sympatric speciation

new species evolve from single ancestral species when inhabiting same geographic region - eg. chromosomal error

artificial selection

selection pressures are artificially created by humans

eg. dairy cow

DNA sequencing

1. DNA sample divided in 4, all containing ATCG, DNA polymerase, primers, modified nucleotides which have been fluorescently labelled

2. modified nucleotide is incorporated into growing chain, replication is terminated (dideoxy)

3. DNA fragments of different lengths formed across reaction vessels

4. high res. electrophoresis used to separate fragments by size

gene sequencing + / -

genome wide comparisons, evolutionary relationships, medical research, personalised medicine, synthetic biology

PCR

1. DNA sample + primers + free nucleotides + DNA polymerase

2. heated to 95C to break H bonds, separates 2 strands

3. cooled to 50~65C for primer annealling

4. 70C - optimum temp for Taq polymerase

gel electrophoresis

separates the DNA fragments and proteins according to their size using electric current

genetic engineering

restriction enzyme cut DNA at specific base sequences + cut plasmid → sticky ends

incubated with plasmids, sealed with DNA ligase

recombinant DNA

transgenic microorganisms

electroporation used to stimulate bacterial cells to take up plasmids

• increases permeability of bacterial membranes → calcium salts, rapid temp change from 0 to 40

• marker gene - identifies if taken up (antibiotic resistance)

somatic gene therapy

target cells only, short term solution, must be repeated

germ line therapy

embryonic cells, permanent which will be passed down to offspring