7.3 Speciation Flashcards
How is variation an advantage?
pops with low variation are not able to withstand change in environments = less likely to have an individual with a phenotype suited for the new environment
What are the 2 types of variation?
discontinuous and continuous
What is discontinuous variation?
distinct groups = no overlapp
involves features that have distinct categories, with no individuals in between
What is continuous variation?
a range of characteristics that change gradually
How are phenotypes measured in continuous and discontinuous variation?
discontinuous = qualitative phenotypes
continuous = quantitative phenotypes
How many genes is each type of variation controlled by?
discontinuous = 1/2 genes with multiple alleles
continuous = polygenic - controlled by many genes
What effect does the environment have on discontinuous variation?
little effect from environment on gene expression
What effect does the environment have on continuous variation?
more significant effect from the environment on gene expression
What is an example of discontinuous variation?
blood groups in humans - A B O
What is an example of continuous variation?
heights, body weight
What are the main 2 sources of variation?
genetics and environment
What are the 2 genetic causes of variation?
mutations and meiosis
How does meiosis cause variation?
crossing over
sexual recombination
random assortment
random fertilisation
How does the environment cause variation?
can change a phenotype over time due to changed lifestyles
What is the process of natural selection?
- new alleles for a gene are created by random mutations
- genetic variation rises in pop
- if environment changes = leads to competition/predation/ disease
- if the new allele increases the chances of survival in that environment more likely to survive and reproduce
- reproduction passes on the advantageous allele
- over many generations the new allele increases in freq in the gene pool
What is evolution?
the change of the allele frequencies in a population over time
Why does Hardy-Weinburg disagree with evolution?
the allele freq are constant
What is selection pressure?
any environmental pressure that limits the population or kills individuals, results in differential survival and reproduction
What is differential survival and reproduction?
some individuals are more likely to survive and reproduce at the expense of others
What is an example of a selection pressure?
antibiotics use in the development of antibiotic resistance in bacteria
What is disruptive selection?
favours either of the extreme phenotypes
What is speciation?
the evolution of new species from exisiting ones
What is the process of speciation?
- pops are reproductively isolated
- no gene flow between isolated groups - they cannot interbreed
- different mutations occur in DNA of each group
- because they are exposed to diff environments
- subject to diff selection pressures
- natural selection = diff gene pools of each group
- diff genetics expressed as diff phenotypes
- no longer interbreed to form fertile offspring = diff species
What is genetic drift?
no selective pressures
there is no favoured phenotype in the pop and only a few individuals can survive the change in the environment
What can be said about individuals who have survived genetic drift?
each individual represents a large proportion of the pop in a small pop as not many individuals will survive the change in environment
What are the 2 types of genetic drift?
the bottle neck effect and the founder effect
What type of population does the bottle neck effect occur in?
very genetically diverse populations
What is the bottleneck effect?
a type of genetic drift that occurs when a population’s size is severely reduced, often by a natural disaster reducing the genetic diversity of a pop
How is the bottleneck population diff to the original pop?
small pop with a random group of survivors
they will have a diff allele freq to the original pop and some alleles may be missing entirely
reduced genetic diversity of new pop
What effect does reducing genetic diverity have on the bottleneck pop?
reduced genetic diversity = makes it difficult for pop to adapt to new selection pressures
they are more vulnerable to environment changes
Why is a less genetically diverse pop more vulnerable to environment changes?
they are less likely to have alleles that are advantageous to the new envrionment
What is the founder effect?
a type of genetic drift that occurs when a small group of individuals break away from a larger population to establish a new colony
What effects does the founder effect have?
genotypic and phenotypic differences to original pop
inherited diseases
speciation
What is the difference between the bottleneck effect and the founder effect?
bottleneck occurs when most of the pop is destroyed
founder = small group breaks away
What are the 3 main causes for differential survival and reproduction?
predation
disease
competition
What is differential reproductive success?
not all individuals are as likely to reproduce and this results in change in allele frequencies within a gene pool
How does disruptive selection lead to speciation?
either extreme train is selected for = more likely to survive and pass on genes
the allele freq changes and more individuals possess the allele for the extreme train and the average trait becomes less frequent
continued disruptive selection leads to speciation
What does reproductively isolated mean?
there are 2 populations of the same species but they cannot interbreed together
What is allopatric speciation?
populations become separated geographically leading to reproductive isolation
What is sympatric speciation?
a population of species is reproductively isolated without geographical separation
What is are 2 examples of sympatric speciation?
random mutation may cause individuals to perform a different courtship ritual
individuals become fertile at different times of the year
What are the 4 ways species can change due to sympatric isolation?
mechanical
behavioural
ecological
temporal
How do pops change mechanically due to sympatric isolation?
gametes are no longer compatible
changes in reproductive organs = anatomical changes
How do pops behaviours change due to sympatric isolation?
a random mutation can cause changes in mating behaviours like courtship rituals
How do pops change ecologically due to sympatric isolation?
changes in the way the individuals use the environment - populations rarely meet due to different uses of the environment and how they live within the same environment eg - nocturnal animals
How do pops change temporally due to sympatric isolation?
animals and plants can go into season at different times of the year which make them less compatible with their mates
eg - dogs going into season
plants have different times of the year which they flower
