Genetics, Biodiversity and Classification Flashcards
Species
- similar DNA sequence
- same ecological niche
- can breed to produce fertile offspring
Genetic diversity
Total number of different alleles in a population
Genetic mutation
Random change in base sequence of DNA
Causes of genetic mutation
- spontaneously during DNA replication
- high energy radiation / ionising radiation
- carcinogens
Describe impact of deletion of nucleotide from original DNA sequence
Alters reading frame of gene downstream of mutation - potential to change all triplets so affects formation of multiple amino acids
Chromosome mutation
Change to structure or number of chromosomes
Non-disjunction
Failure of homologous pairs/ sister chromatids to separate during meiosis so cells have fewer or more chromosomes after fertilisation
Polyploidy
More than one complete set of chromosomes
Homologous Pair
Pair of chromosomes - maternal and paternal
Same gene loci
Importance of meiosis
- number of chromosomes halved so diploid number is restored at fertilisation
- genetic variation from independent segregation and cross over
Cross over
- homologous pairs come together in a bivalent and their chromatids becomes twisted forming a chiasma
- equivalent LENGTHS OF non sister CHROMATIDS exchanged
- new combinations of alleles
Independent Segregation
- formation of random combinations of maternal and paternal chromosomes in a homologous pair during metaphase I (meiosis)
- chromosomes of each homologous pair sort into gametes independently of another pair
Meiosis - Prophase
DNA condenses so chromosomes are visible
Nuclear envelope breaks down
Spindle fibres form
(1) cross over occurs
Meiosis - Metaphase
Spindle fibres attach to chromosomes and they align at equator
(1) in homologous pairs - independent segregation/crossover
(2) random alignment of sister chromatids
Meiosis - Anaphase
Spindle fibres contract and shorten
(1) one chromosome from each homologous pair migrates to opposite pole
(2) chromatids pulled apart
Meiosis - Telophase
Nuclear envelope reforms and chromosomes unravel
Importance of genetic diversity
- species more likely to survive environmental change
- greater probability an individual posses allele which allows it to survive
What is evolution and what factors cause it to take place
Change in allele frequency over time
- genetic variation
- selection pressures
Natural Selection
- genetic MUTATIONS create different alleles
- SELECTION PRESSURE
- certain alleles are advantageous
- individuals with this allele more likely to survive and reproduce so have selective advantage
- frequency of allele increases
Evidence for evolution
- genetic code and ATP is universal
- all proteins formed from same 20 amino acids
Reasons for classifying organisms
- easier to study
- understand evolutionary relationships
- keep track of changes
Artificial classification and its benefits/drawbacks
Grouping organisms based on FREQUENCY of similar observable characteristics (phenotype)
- stable classification
- simplified method of grouping individuals
- individually are usually not phylogenetically related since phenotype affected by environment
- provides limited information (cannot sort into species etc.)
Phylogenetic Classification
Grouping organisms based on evolutionary relationships where shared features are derived from a common ancestor
Evidence of phylogenetic classification
- common ancestors
- proportion of similar DNA since mutations occur over time
- comparison of amino acid sequences in cytochrome C (found in all eukaryotes)
- immunological comparisons of proteins using antibodies
Suggest why amino acid sequence of two closely related organisms is the same but they have a different genetic code
Genetic code is degenerate so may have a different base sequence which codes for all the same amino acids
Hierarchy
- groups contained within larger composite groups
- no over lap
Linnaeus Classification
Domain, Kingdoms, Phylum, Class, Order, Family, Genus, Species
Dumb kids playing catch on freeways get smashed
Courtship
Members of the same species use the same sequence of behaviours to communicate with mates
Suggest how courtship leads to successful reproduction
- recognise members of their own species and of opposite sex
- identify mate capable of breeding to ensure synchronised mating
Suggest how courtship is important in the survival of offspring
- form a pair bond so both parents raise offspring to maximise chances of survival
- female can choose a strong and healthy mate which improves survival chances of offspring as advantageous alleles are passed on
Biodiversity
Number and variety of living organisms in an area
Factors to consider when investigating biodiversity
- species richness
- genetic diversity
- ecosystem diversity (range of habitats)
Species Diversity
- species evenness
- species richness
Suggest why species diversity in a desert is low
Only a few species have necessary adaptations to survive harsh conditions
Community
All living organisms in an ecosystem at a given time
Ecosystem
All living and non living components of an area
Ecological niche
Role of an organism in its environment
Habitat
Physical environment where an organisms lives
Species richness
Number of different species only
Suggest how farming reduces species diversity
- undesirable species are outcompeted by farmed species in terms of space and resources
- pesticides
- eutrophication due to fertilisers
Deforestation
Action of removing a wide area of trees
Causes of deforestation
- Agricultural farming
- Livestock farming
- Over population so infrastructure expansion
- Logging
Solutions to low species diversity
- hedgerows rather than fences
- biological control instead of pesticides
- organic fertilisers
- crop rotation
Explain what is meant by a stabilising selection and describe the circumstances under which it takes place
- occurs in an unchanging environment
- individuals with phenotype closest to the mean are best adapted
- selection against extremes
- mean is unaltered
- range of phenotypes is reduced
- increasing proportion of population well adapted to environment
Explain what is meant by directional selection
- environmental change
- extreme phenotype is favored over other phenotypes so more likely to survive and reproduce
- whole distribution shifts over time in the direction of the favoured phenotype
Speciation
Formation of a new and distinct species
Describe how speciation occurs
- individuals of same species are isolated
- have their own unique selection pressures
- acquire different allele frequencies over time
- genes become so different they can no longer breed to produce fertile offspring
Explain factors which give rise to variation which results in different phenotypes
- different environments with different selection pressures
- mutations to genetic code
- crossover and independent segregation during meiosis
- random nature of sexual reproduction
Suggest why gene technologies are now used to classify organisms over traditional methods
- more accurate
- easier to carry out
Normal Distribution
Distribution of random variables represented by a symmetrical bell-shaped curve
What is meant by closely related in terms of evolution
Close common ancestor
When does cross over occur
Between prophase 1 and metaphase 1
Suggest why individuals may have similar observable characteristics even though they are different species
- could be closely related instead
- could have evolved in same environment
- characteristics could be polygenetic
Under what environmental conditions does directional selection occur
Slow changing environment in one direction
Describe how immunological comparisons between species are made
- protein from blood serum of test 1 species is extracted
- injected into another species so antigens produce an immune response
- blood serum extracted from injected species containing antibodies
- added to blood serum of test 2 species containing same protein to be tested
- level of precipitation determines how closely related both test species are
State comparisons of genetic diversity that scientists use in order to generate classifications for organisms
- base sequence of DNA
- base sequence of mRNA
- amino acid sequence of common proteins
Suggest why population of animals has low genetic diversity
- hunting
- small population due to genetic bottle neck (sharp reduction in population size due to natural disaster)
- founder effect (descended from a small number of ancestors)
Explain how hunting reduces genetic diversity
- reduced population size
- founder effect
- inbreeding
Explain why small population means low genetic diversity
- only a few copies of genes passed on
- not all alleles of genes included
Explain why an area has higher biodiversity
- greater variety of habitats
- greater variety of food sources
- more niches
- more plant species
- more animal species
How to calculate number of genetically distinct cells produced from independent segregation given chromosome number
2^chromosome number
Option to 2 cells and 8 to choose from
Justify whether two organisms are same species / part of same hierarchical group
- recent divergence
- same branch in phylogenic tree
- recent divergence means share close common ancestor or similar bas sequence
- phylogeny based on classification
- shared anatomy
- old classification based on anatomy but new biochemical data more accurate
- scientific knowledge develops over time
