Full class notes for IGCSE Biology Unit 5 from the Pearson Edexcel syllabus. Unit 5: Use of biological resources
Sub-topics:
a) Food production
b) Selective breeding
c) Genetic modification (genetic engineering)
d) Cloning
Difference btwn individuals of same species
Beneficial cos allows natural selection + reduces risk of extinction
CAUSES
Genetic variation
o Each org has different DNA cos of genetic variation in meiosis
o Different alleles = new set of genes made
Environmental variation
o Characteristics affected by climate, diet, accidents, culture, lifestyle
Genetic + environmental variation
o Phenotype of org based on genetic + environmental characteristic
o Potential height decided by genes but due to lack of nutrient from environment it wont
o
CAUSES OF GENETIC VARIATION IN SEXUAL REPRODUCTION
VARIATION IN GAMETES COS MEIOSIS
Meiosis creates haploid no. of chromosomes from diploid no.
Gametes formed by meiosis + don’t have same combo of alleles = genetic variation
Crossing over btwn homologous pairs of chromosomes introduce variation
Separation of homologous pairs in daughter cells causes variation
RANDOM FERTILISATION DURING SEXUAL REPRODUCTION
Sperm could fertilize w ovum = zygote = genetic variation of offspring
Every living thing is genetically different
Cos gametes genetically different + fusion of gametes completely random
MUTATIONS
Random changes in DNA/genetic material coding for different protein
EVOLUTION
Change in inherited characteristics w in ppltn over time thru natural selection
New species arise from existing species + others become extinct
Mechanism of evolution proposed by Darwin
Based on 3 main observations
o w/in ppltn organisms have varying characteristics + inherited by offspring
o org produce ^ offspring than needed to replace parents
o on ave, ppltn size remains relatively constant
2 conclusions
o Struggle for existence – many offspring but ppltn constant = compete for available
resources = many die
, o Survival of fittest – best adapted org get selective advantage + survive to reproduce
Advantageous allele passed to offspring = frequency of allele ^
NATURAL SELECTION
Natural process where best adapted individuals survive longer, have ^ offspring + spread
characteristics
Mechanism of evolving of new species
Allows different forms of species to survive in different environments
Theory of natural selection proposes factor in env selects which form of species survives to
reproduce = not well adapted will not survive
Evidence for natural selection must show that
o There is variation w in species
o Selection pressure – environmental conditions change
o Selective advantage – favors on particular form of individual in species
o Frequency of favored allele ^
o Frequency of disadvantageous allele decreases
o Allele frequency of ppltn changes
EXAMPLES OF NATURAL SELECTION
SNAIL SHELL COLOUR
Variation of shell color in ppltn of snails
Normal varieties = black/grey
Chance mutation = white shelled which survive longer cos better camouflaged
^ reproduction oppo = pass allele to offspring
Majority of snails have white shells = change in frequency of phenotype in ppltn over time
PEPPERED MOTH
Variation w in peppered moth ppltn w light + dark moth
Natural selection favored dark colored moths in areas of heavy pollution
Light colored favored in less polluted areas
NATURAL SELECTION + ANTIBIOTIC RESISTANCE
Antibiotic kills/inhibits growth + reproduction of bacteria
Bacteria reproduce every 20 min = evolution occurs in shorter time span
Variation caused by mutation
Chance mutation causes bacteria = ^ resistant to antibiotic
When treated w antibiotic = resistant bacteria wont die
Reproduce w less competition from non-resistant bacteria
Genes for resistance passed at ^ frequency to next gen
Whole bacteria ppltn eventually resistant = natural selection
^ in antibiotic resistance = harder to control infections + diseases
OTHER EXAMPLES OF NATURAL SELECTION
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