Topic 4: Genetic information, variation and relationships between organisms

eukaryotic DNA

long

linear

associated with histones/proteins

contains introns

prokaryotic DNA (mitochondrial/chloroplast)

short

circular

not associated with histones/proteins

does not contain introns

gene

base sequence of DNA that codes for the amino acid sequence of a polypeptide which combine to make proteins

and function RNA like rRNA/tRNA

intron

non-coding section of DNA

exon

coding section of DNA

degenerate code

some amino acids have more than one coding triplet (codon)

universal code

the same codon codes for the same amino acid in all organisms

non-overlapping code

each base is part of only one codon

triplet

sequence of three DNA bases codes for a specific amino acid

locus

position of a gene along the DNA molecule

chromosome

long, coiled DNA molecule and its associated proteins/histones

homologous chromosomes

pairs of chromosomes containing the same sequence of genes but alleles may be different

one maternal, one paternal

alleles

different forms of the same gene

transcription

1. DNA helicase breaks H bonds and unwinds the DNA molecule
2. strands separate
3. one strand acts as a template/sense strand
4. RNA nucleotides are attached to exposed bases and pair with complementary, specific bases
5. Thymine replaced by Uracil, and Adenine complementary to Uracil and Cytosine complementary to Guanine
6. RNA polymerase joins RNA nucleotides forming single strand of (pre-)mRNA by phosphodiester bonds

translation

1. mRNA attaches to ribosomes
2. tRNA anticodons bind to complementary mRNA codons
3. tRNA brings specific amino acid
4. amino acids join by peptide bonds by condensation reactions with use of ATP
5. 2 tRNA molecules bind at a time
6. tRNA released
7. ribosome moves along the mRNA to form the polypeptide

genome

complete set of genes in a cell

all DNA in a cell

proteome

full range of proteins that the cell is able to produce

mutation

involve a change in the base sequence of chromosomes

arise spontaneously during DNA replication

mutagenic agents

increase the rate of gene mutations

eg. x-rays, uranium, tobacco tar, caffeine

deletion mutation

DNA nucleotide is lost

resulting in a frameshift to the left so all triplets from this point will be read differently

substitution mutation

nucleotide is replaced by a different base

degenerate code may mean no effect to amino acid sequence

else, if amino acid with specific role changes this can form new bonds and alter the tertiary structure

how meiosis forms haploid cells

1. chromosomes condense
2. chromosomes associate in to homologous pairs
3. chiasmata forms
4. join to spindle fibres by centromere
5. align at equator of cell
6. chromosomes move to opposite poles
7. chromatids separate in 2nd division

meiosis is important

to maintain chromosome number between generations, all cells produced are haploid so when fertilisation takes place a diploid cell is produced

introduce genetic variation through independent assortment of homologous chromosomes, crossing over, and random fertilisation of gametes

crossing over

1. homologous chromosomes associate
2. lead to formation of chiasmata and crossing over can occur
3. result in a new combination of alleles

random/independent segregation of homologous chromosomes

1. chromosomes can align randomly
2. known as independent segregation
3. producing varying combinations of chromosomes/alleles

non-disjunction

when homologous chromosomes/chromatids fail to separate into sister chromosomes/chromatids

gametes may have an extra or no copies of chromosomes

difference between mitosis and meiosis

1. mitosis has one cell division whereas meiosis has two cell divisions
2. in mitosis the number of chromosomes stay the same whereas in meiosis the number of chromosomes half
3. in mitosis the daughter cells are genetically identical whereas in meiosis the daughter cells are genetically different
4. in mitosis there are no chiasma formed nor crossing over whereas in meiosis there are chiasma formed and crossing over
5. mitosis is for growth and repair whereas meiosis is for producing gametes
6. mitosis for asexual reproduction whereas meiosis for sexual reproduction
7. mitosis produces 2 daughter cells whereas meiosis produces 4 daughter cells

how mutations produce genetic variation

1. genetic variation arises by spontaneous mutations
2. resulting in new advantageous alleles
3. organisms are more likely to survive and reproduce more
4. passing the advantageous allele to the next generation
5. so, the frequency of the allele increases over subsequent generations

microbial practical: aseptic techniques

wipe down surface with antibacterial cleaner before and after experiment

use a Bunsen Burner in work space so convention currents draw microbes away from culture

flame the wire loop/inoculating loop

flame the neck of bottles before to prevent bacteria entering the vessel/air moves out so unwanted organisms do not enter

keep all vessels containing bacteria open for the minimum amount of time

close windows and door to limit air currents

wash hands thoroughly

microbial practical: why incubate at 25°C

so the bacteria does not grow at body temperature and is not harmful to people

microbial practical: what is the clear zone around the antibiotics

inhibition zone, where bacteria has been killed by the antibiotic diffusing in to the agar jelly

larger the area of inhibition, the better the antibiotic works

microbial practical: how to calculate area of inhibition zone

πr^2

π = 3.14

r = radius of the inhibition area

(r = half the diameter)

microbial practical: what does no inhibition zone mean

the bacteria is resistant to the antibiotic and none has been killed

microbial practical: why must you not tape around the whole agar plate

this blocks air flow into the plate thus promoting the growth of anaerobic bacteria, which are harmful

genetic diversity

number of different alleles of a gene in a population

enables natural selection to occur

gene pool

all the different alleles (of all genes) in a population at a given time

selection

process by which organisms that are better adapted to their environment survive and breed

passing their advantageous alleles down generations

stabilising selection

natural selection that keeps allele frequency relatively constant over generations

no change in environment means that the most favourable allele is the mean

directional selection

gradual change in allele frequencies over several generations

change in environment or new advantageous allele leads to shift in mean

example of selecting selection

birth weights moves to mean

too heavy = too painful for mothers

too light = high surface area to volume ratio so too difficult to maintain body temperature

example of directional selection

antibiotic resistant bacteria

more likely to survive and reproduce with antibiotic resistant allele

types of adaptation

behavioural

anatomical

physiological

phylogenetic classification system

arranges species into groups based on their evolutionary origins and relationships

species

two organisms that can reproduce together to produce fertile offspring

hierarchy

large groups divided into smaller groups with no overlap between groups

common features/shared characteristics of species

anatomy

fossils

embryology

DNA

meaning for DKPCOFGS

domain

kingdom

phylum

class

order

family

genus

species

binomial system/nomenclature

first word = genus (capitalised)

second word = species (lower case)

in italics/underlined

eg. *Homo sapiens*

courtship behaviour

behaviour/series of acts that result in mating/reproduction

to enable species recognition

how courtship behaviour increases the probability of successful mating

recognition of same species, ensures mating takes place between members of the same species

recognition of mate/opposite sex

stimulate release of gametes

indication of sexual maturity/fertility

species richness

measure of the number of different species in a community

index of diversity

describes the relationship between number of species in a community and the number of individuals in each species

index of diversity equation

d = N(N-1) / sum of n(n-1)

index of diversity equation: d

index of diversity

higher the value of d, greater the species diversity

index of diversity equation: N

total number of organisms of **all** species

index of diversity equation: n

total number of organisms of **each** species

difference between species richness and index of diversity

species richness measures only number of different species, does not measure the number of individuals

effect of deforestation on species diversity

reduce number of trees, reduce number of trees species

destroys habitat so species lose shelter and food sources meaning species may die/migrate, reduce diversity

effect of agriculture on species diversity

farmers try to maximise the amount of food they can produce by

removing hedgerows for crop space

woodland clearance

monoculture

pesticides

herbicides

conservation

protection of an organism, habitat, or species in attempt to maintain diversity and ecosystem

how genetic diversity within/between species be compared

frequency of measurable or observable characteristics

base sequence of DNA

base sequence of mRNA

amino acid sequence of proteins encoded by DNA and mRNA

comparing frequency of measurable and observable characteristics **limitations**

lots of charactersitics are coded for by more than one gene (polygenic)

difference could arise due to environmental conditions rather than alleles

comparing base sequence of DNA

accurately determine the exact order of nucleotides

two species DNA are very similar

how to compare DNA base sequence

compare DNA

sequence of bases/nucleotides

DNA hybridisation

separate DNA strands/break hydrogen bonds

mix DNA/strands

temperature/heat to separate strands indicate relationship

comparing base sequence of mRNA

mRNA is complementary to the strand of DNA

however, introns are spliced out of pre-mRNA to form mRNA

comparing amino acid sequence

more closely related equals more similarities in amino acid sequence of same protein

amino acid sequence is determined by DNA base sequence

however, code for amino acid is degenerate and introns are spliced out of pre-mRNA to form mRNA