3.7.2 Population and Evolution Flashcards
What is continuous variation ?
when the individuals vary in a range so there are no distinct categories
What is discontinuous variation ?
When there are two or more distinct categories and each individual falls into only one category
Give examples of continuous variation
Give examples of discontinuous variation
What causes variation in phenotypes?
The organisms genotypes and the environment
name 3 sources of genetic variaion
Mutation, meiosis (independenet assortment and crossing over) and random fusion of gametes
How does the use of Hardy Weinberg equation allow us to see if evolution has occurred?
Identify changes in the allele frequency over time, if allele frequency has changed then selection has occurred. Also if you do the maths and either of the HW equations doesn’t add to 1 then this suggest evolution
What is a gene pool?
All the alleles of all the genes in a population at a certain time
How can looking at phenotype help to measure genetic diversity of a species?
Different phenotypes are coded for by different alleles, so the larger the number of different phenotypes, the greater the diversity of alleles so the greater the genetic diversity
How can looking at genotype help to measure genetic diversity of a species?
Analyse the sequence of base pairs in DNA samples of organisms. The order of bases in different alleles is slightly different. By sequencing the DNA of individuals of the same species, you can look at similarities and differences in the alleles. The larger the number of dif alleles the greater the genetic diversity
Define ‘selection pressure’
environmental factors that limit the population of a species
Define ‘directional selection’
When individuals away from the mean are selected for. One extreme is selected in favour of the other so the normal distribution shifts in one direction
Define ‘disruptive selection’
When individuals away from the mean are selected for. Individuals at both extremes are selected in favour of those near the mean so the normal distribution becomes ‘squashed’ in the middle
Draw the effects of 3 types of selection pressure on this curve
insert pic
scroll through all pictures
2 answers
Explain how natural selection has lead to antibiotic resistance
Chance mutation, new allele, selection pressure, bacteria with resistance survive and pass on allele, increase in allele frequency,
What happens to individuals with the advantageous alleles?
They are more likely to survive, reproduce and pass on their advantageous alleles to their offspring
what is speciation
The evolution of new species from existing ones.
What are the two types of speciation
Allopatric - when populations become geographically separated. Sympatric - speciation that occurs in the same geographic area
What is reproductive isolation?
When changes in the alleles and phenotypes of the populations prevent them from successfully breeding together
what is hybrid sterility and give an exampe
when two different species can breed but their offspring are infertile (eg tiger + lion = liger)
Why might a population become reproductively isolated?
Due to geographical isolation or random mutations
How does geographical isolation lead to speciation?
Conditions on either side of the barrier are slightly different. Different characteristics will be advantageous on each side so the allele frequencies change in each population. Mutations occur independently in each population, also changing the allele frequencies. The changes in allele frequencies lead to changes in phenotype frequencies. Eventually, the different populations become genetically distinct and are reproductively isolated
What does it mean when organisms are reproductively isolated?
The individuals from the different populations will have changed so much that they won’t be able to successfully breed with each other to produce fertile offspring
What is adaptive radiation
A population of organisms spreads to many new habitats. In each new habitat different selection pressures exist that result in the formation of multiple new species from one ancestor (eg Darwin’s finches)
What is genetic drift
When allele frequencies (especially in small populations) change over time due to random changes and random mating
What is a genetic bottleneck
When allele frequencies in a population can change if a population decreases drastically in number (eg due to a natural disaster) and then repopulates
Define allele frequency
How often an allele occurs in a population
Under what conditions is the Hardy Weinberg principle true?
Large population, random mating, no natural selection, no mutations, no immigration or emigration
what are the two hardy weinberg equations
p + q = 1 and p^2 + 2pq + q^2 = 1
What does p stand for in p + q = 1?
the frequency of the dominant allele
What does q stand for in p + q = 1?
the frequency of the recessive allele
what does p^2 stand for in p^2 + 2pq + q^2 = 1?
the frequency of the homozygous dominant genotype
what does 2pq stand for in p^2 + 2pq + q^2 = 1?
the frequency of the heterozygous genotype
what does q^2 stand for in p^2 + 2pq + q^2 = 1?
the frequency of the homozygous recessive genotype
Define evolution
When frequency of an allele in a population changes over time
What is allopatric speciation
Formation of a new species due to geographical isolation
Define speciation
When a new species develops because populations of the same species become reproductively isolated, reducing gene flow between the two populations
What is sympatric speciation
The formation of a new species without geographical isolation due to random mutations which produce changes in phenotype
