3.4 Genetic information, variation and relationships between organisms Flashcards
What are the features of DNA molecules in prokaryotic cells
Short, circular and not associated with proteins
What are the features of DNA molecules in eukaryotic cells?
Long, linear, found in the nucleus and associated with proteins called histones
DNA molecule and its histones form a chromosome
What eukaryotic cell organelles apart from the nucleus contain DNA and how does this differ from the DNA in the nucleus?
Mitochondria/chloroplasts
It’s similar to the DNA of prokaryotes: short, circular and not associated with proteins
A gene is a base sequence that codes for:
- the amino acid sequence of a polypeptide
- a functional RNA (including rRNA and tRNAs).
Define locus
Define proteome
The fixed position that a gene occupies on a particular DNA molecule
Complete set of proteins that a cell can code for
What is a triplet?
A sequence of 3 DNA bases that code for a specific amino acid
Explain how the genetic code is universal, non-overlapping and degenerate
Universal because:
code is the same in almost all organisms
acts as evidence for evolution.
Non-overlapping because:
the first three bases are read as one codon, then the next three as the second etc
therefore each base is read only once and the bases do not overlap.
Degenerate because:
more than one triplet can code for a particular amino acid.
Define genetic diversity
Benefit of it?
What can lower it?
number of different alleles of genes in a population
factor that allows natural selection to occur
Benefit:
-species able to adapt with changes in the environment
-e.g. if a new disease arises, some individuals will have characteristics to survive, and will reproduce passing on their alleles, so the species does not become extinct
Can be lowered by:
-small population size
-e.g. founder effect (the numbers start low)
-or genetic bottleneck (where the numbers decrease)
Define species richness
Number of species in a community
Define species diversity
What is the benefit of it?
How is it measured?
How does deforestation lower species diversity?
How does agriculture/farming lower species diversity?
-number of different species
-number of individuals for each species
-Stable ecosystem
-each species is less likely to become extinct (due to high genetic diversity)
-& if a species does become extinct it will not affect the food chain as there are other species available
-Species Diversity Index
-takes into account the number of different species and how many individuals there are for each species
-the larger the species diversity index, the larger the species diversity
-(deforestation is the removal of trees for wood & space)
-decreases plant species diversity
-less variety of habitats
-less variety of food sources
-decreases animal species diversity
-deforestation to make space for farm
-only grow a few plants & keep a few animal species
-selectively breed plants & animals
-use pesticides to kill other species
Define ecosystem diversity
Variety of ecosystems
Define taxonomy
the science of identifying, describing, and classifying organisms based on their characteristics and evolutionary relationships.
Outline the principles of natural selection in the evolution of populations
- population of species has variation
- Random mutation can result in new alleles of a gene.
- Many mutations are harmful but, in certain environments, the new allele of a gene might benefit its possessor, leading to increased reproductive success.
people with the mutation are more likely to survive and reproduce - The advantageous allele is inherited by members of the next generation.
- As a result, over many generations, the new allele increases in frequency in the population.
Outline the difference between directional and stabilising selection using an example
Directional selection:
-occurs when environmental conditions change, so phenotypes best suited to the new conditions are more likely to survive
-hence these individuals will breed and produce offspring
-overtime the mean population will move in the direction of these individuals
-e.g. bacteria being resistant to antibiotics
-a single bacteria will have had a mutation to prevent being killed by penicillin, e.g. producing the enzyme penicillinase
-allows it to grow and populate
-frequency of the allele that enabled penicillinase production increased alongside the population
-hence population moved to have greater penicillin resistance
Stabilising selection:
-phenotypes with successful characteristics are preserved
-phenotypes with greater diversity are reduced
-this selection doesn’t occur due to changes in environment
-if the environment stays the same then the individuals closest to the mean are favoured because they have the alleles that have given them the survival advantage
-the furthest from the mean are selected against
-e.g. new born babies weights
-those that have a birth weight of around 3kg are more likely to survive than those at the extremes
Define biodiversity
Variety of habitats and species in an ecosystem