1.7 Evolution Flashcards
What is inheritance?
the passing of genes from one organism to another
What is vertical inheritance?
describes the passage of genetic info from parents to offspring
Vertical inheritance - sexual reproduction?
vertical inheritance by sexual reproduction is a slow process as it involves stages of gamete production and fertilisation
It may be influenced by seasons and mating rituals
It results in variation by mixing up parental genotypes
Gametes show variation due to the random way that homologous chromosomes separate to form haploid gametes
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Sexual reproduction results in variation in genotype and phenotype
Vertical Inheritance - Asexual reproduction?
Vertical Inheritance by asexual reproduction is much faster process as it does not involve the production of gametes or fertilisation
It doesn’t produce variation as offspring only come from one parent and not the fusion of gametes
Asexual reproduction forms a clone (a group of genetically identical offspring)
Horizontal Inheritance Prokaryote
Prokaryote Transformation?
a fragment of DNA or a plasmid from one bacterium is taken up from the environment by another bacterium
Prokaryote Transduction?
a virus carries genetic material from one bacterium to another
Prokaryote Conjugation?
A bridge forms between two different bacteria and fragment of DNA or a plasmid is passed from one to another
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Horizontal transfer is the mechanism that introduces variation into prokaryotes
Rapid evolution in prokaryotes?
this means that bacterial genomes can be shared rapidly and they can undergo rapid evolution
consider that transgenic bacteria reproduce asexually and can double in number every 20 mins
MRSA
certain bacteria can exchange plasmids carrying the genes that confer resistance to antibiotics from one bacteria to another
this has resulted in the rapid emergence of strains of bacteria resistant to several antibiotics
MRSA causes infections which are extremely difficult to cure and which sometimes prove to be fatal
Horizontal Inheritance Prokaryote
eukaryote viruses?
some viruses can insert their genome into the host cell’s genome
many non-coding introns are thought to be the result of viral genetic integration
e.g. HIV retrovirus can be spliced into the DNA of the host white blood cell
eukaryote agrobacterium?
bacteria such as agrobacterium tumefaciens can transfer their DNA directly into eukaryotic plant cells
this is useful in genetic engineering
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Horizontal transfer is the mechanism that introduces variation into prokaryotes
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dont be tempted to identify vertical or horizontal inheritance patters according to how diagrams are laid out - a horizontal arrow on a diagram does not necessarily mean horizontal inheritance
What is natural selection?
non random increase in the frequency of those specific genes which increase an organisms chance of survival
What are the stages of natural selection?
- Organism produce more offspring than the environment can support
- Genetic variation occurs within individuals of a population
- Individuals compete for available resources such as food and mates
- Individuals with favourable genes which give them an advantage in the environment such as the ability to find prey and more likely to survive and pass genes onto the next generations
- Frequency of these favourable genes increases within the population. Individuals without these favourable genes gradually begin to die out.
Example evolution of resistant insects?
pest insects include mosquitoes which transmit diseases such as malaria and yellow fever and locusts which destroy crops
DDT is a poisonous chemical widely used against many insect pests
Resistance to DDT occurred due to a mutation
Resistant insects are able to make an enzyme that renders DDT harmless
These mutants were already in the population naturally in small numbers and were not produced as a result of DDT use
When DDT is first applied the vast majority of insects died as they were not resistant
the few resistant in the population survived, enjoying a selective advantage
resistant insects reproduced passing on the mutant advantageous gene for resistance to the next generation
resistant insects increase in frequency in the population
DDT is now ineffective in treating many species of insect
IMPORTANT NOTE ON NATURAL SELECTION
change in environment does not cause mutation
the mutant allele is already present in the population in small numbers
the change in environment allow the mutation to have a selective advantage and increase in numbers in the population
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Natural selection can affect gene frequencies in two ways
advantageous mutations - non random increases in alleles
deleterious mutations - non random decreases in alleles
What is sexual selection?
the chances of successful reproduction are increased if a sexual partner is selected on the recognition and non random selection of strong genetic traits
- male/male rivalry
- female choice
male/male rivalry?
males compete with physical aggression to access for females
e.g. stags
female choice?
selection of a male based on a high quality visual display of genetic traits, his ability to outcompete other males, protect territory, his skills at nest building or performing mating rituals
e.g. eye spots on feathers of male peacock, lrger the more attractive
What are quantitative traits?
quantitative traits are continuous variables due to polygenic inheritancee
when you plot data for continuous variables in a large population you should get a normal distribution curve
What is continuous variation?
characteristic changes gradually from one extreme to another
What is polygenic inheritance?
characteristic determined by the interaction of more than one gene
What are the three ways that natural selection can affect the frequency of a measurable trait within a large population?
stabilising selection
disruptive selection
directional selection
What is stabilising selection?
stabilising selection occurs within a stable environment and selects for the mean value/range of a genetic trait within a population, avoiding the more extreme versions of the trait
What is directional selection?
direction selection occurs within a changing environment and selects for a lesson common version of a genetic trait within a population resulting in an increase in frequency
what is disruptive selection?
disruptive selection occurs when two different environments or resources become available and selection is for the: most extreme versions of a genetic trait, resulting in the population splitting into: two distinct groups
What is a gene pool?
The total of all the different alleles in a population is called the gene pool
If a species is under no selection pressure frequencies of individual alleles will stay the same from generation to generation
REMEMBER!
An allele is a form of a gene
What is genetic drift?
is a random increase or decrease in the frequency of DNA sequences within the gene pool of a population
As a result of chance events, neutral mutations and by colonisation and the founder effect.
It is most prevalent in small populations
What is the founder effect?
specific alleles of genes may have different frequencies or may be lost when some organisms becomes isolated from the main population and ‘found’ a new separate population (splinter group)
The new population contains a random selection of alleles from the parent population.
Genetic drift and neutral mutation?
the combined effect of more than one neutral mutation could result in a selective advantage or disadvantage
this is rare in large populations and it is very rare for two individuals with neutral mutations to meet and breed
in a splinter group the neutral mutations may represent a higher percentage, increasing the chances of two individuals meeting and producing offspring who passes both mutations
selection pressures then work to change the frequency of the neutral mutation
What is the bottleneck effect?
the majority of a population may die out due to a natural disaster and a large number of genes are lost
survivors may carry a small random selection of genes from the original population
this results in a change in frequency of alleles in a population and significant loss of genetic variation
What is a species?
a group of organisms that can interbreed to produce fertile offspring
REMEMBER!
remember that different species do not produce fertile young when they interbreed. Only fertile young can be produced with members of the same species
What is speciation?
speciation is the evolution of two or more species from a common ancestor
Explain process of speciation?
Large population with common gene pool
isolation - two populations separated by a barrier
Mutation - mutation gives rise to new alleles
natural selection - selection pressures are different for each population: temperature, predation
this gives different characteristics a selective advantage allowing them to accumulate in the population
time - after a long period of time if the barrier is removed there is no interbreeding
What are the two types of speciation?
allopatric
sympatric
What is allopatric speciation?
occurs when isolation of subpopulations is by a geographical barrier such as a river, desert, mountain or sea
What is sympatric speciation?
occurs when isolation of subpopulations is given by a behavioural or ecological barrier or due to polyploidy occurring within a population
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isolation barriers prevent interbreeding and gene flow between subpopulations
What are hybrid zones?
exist where interbreeding is possible and as a result genes are able to flow between subpopulations (overlaps)
they form where the ranges of two closely related species overlap
within these hybrid zones members of the two species can interbreed but the hybrids formed are less fit or sterile and are eliminated by natural selection
members of each species continue to colonise the hybrid zone and undergo hybridisation to populate
Size of hybrid zone?
hybrid zone - narrow
indicates two overlap populations are genetically distinct species
wide
greater genetic variation within overlapping population
