Variation and evolution Flashcards
(49 cards)
1
Q
What is a gene pool?
A
- all the alleles of all the genes of all the individuals in a population at any one time
2
Q
what is an allele frequency?
A
- a measure of the relative frequency of an allele on a genetic locus in a population
3
Q
Define variation?
A
- different allele combinations produced in each generation
- different phenotypes in a population
4
Q
Name the types of variation?
A
- continuous and discontinuous variation
- heritable and non heritable
5
Q
what is continuous variation?
A
- type of variation that cannot be categorised
- influenced by multiple genes and often significantly affected by environmental factors
- range of phenotypes between 2 extremes i.e height
6
Q
what causes continuous variation?
A
- both heredity and environment which influences the phenotype appearance of the characteristic
7
Q
what is discontinuous variation?
A
- controlled by a single gene
- no intermediate forms
- can be categorised i.e blood group
8
Q
When comparing data showing different types of variation, discontinuous data is compared using:
A
-numbers or percentages in each group
-the ratio of the numbers in one group compared to another.
9
Q
How can distinguish discontinuous data from continuous?
A
- continuous variation will have data around the mean, mode and median.
- discontinuous data will have two discrete groups that are non-overlapping.
10
Q
compare heritable and non heritable variation?
A
- heritable variation is the genetic differences between individuals
- non heritable variation is aquired differences in the phenotypes of individuals that cannot be inherited (environmental influences)
11
Q
what causes variation in individuals?
A
- environmental factors
- epigenetic factors i.e diet, smoking
- sexual reproduction
- mutations
12
Q
How does sexual reproduction cause variation?
A
- random cross fertilisation (mixing of two different parental genotypes)
- random assortment of chromosomes during metaphase 1 and chromatids in metaphase 11
- crossing over between homologous chromosomes during prophase 1
13
Q
What are causes of variation in populations?
A
- competition between organisms ( intra and inter )
- selection pressure
14
Q
define evolution?
A
- the change in allele frequency in a gene pool of a population over time
- occurs due to natural selection
15
Q
how does natural selection cause a change in allele frequencies over generations?
A
- random mutations in populations
- organisms with the advantageous characteristics are more likely to survive the selective pressure
- survive and reproduce
- pass on their advantageous alleles to next generation
- over many generations, the allele frequency of the favourable characteristic will increase.
- frequency of unfavourable alleles will decrease
16
Q
what is it meant by selective pressures?
A
- environmental factors that drive evolution by natural selection and limit population sizes
- change the frequency of alleles in a population
17
Q
give examples of selective pressures?
A
- predation
- disease
- environmental conditions ( temperature)
- competition (habitats, food, mates)
18
Q
what are the impacts of selective agents on the survival of organisms?
A
- breeding sites
- climate
- supply of food
19
Q
what is the different between selective pressure and agent?
A
-The Selective Agent is the environmental factor acting on the population.
-The Selection Pressure is the effect of Natural Selection acting on the population.
20
Q
What is the effect of selection pressure?
A
- the frequency of alleles within the gene pool
- the survival of different phenotypes in a population i.e camouflage, selective predation
21
Q
What do selection pressures change?
A
- the allele frequencies of the alleles present at a particular gene locus in a population
22
Q
how can allele frequency be expressed?
A
either as a proportion or percentage of the total number of copies of all alleles for that gene
23
Q
What does the hardy weinberg principle state?
A
the frequencies of dominant and recessive alleles and genotypes will remain constant from one generation to the next.
24
Q
What does the hardy weinberg principle measure?
A
- allele frequency
25
State the assumptions made by the hardy weinberg
- no mutations
- population is isolated i.e no immigration or emigration
- random mating throughout the population
- no selection for or against any phenotype
- there is a large population
26
What is the hardy weinberg equation?
- p2 + 2pq + q2 = 1
27
What does p, q, p2, 2pq, and q2 mean?
- p2 = frequency of homozygous dominant allele
- q2 = frequency of homozygous recessive
- 2pq = frequency of heterozygous
p = frequency of dominant allele
q= frequency of recessive allele
28
Define speciation
the formation of new species due to the evolution of two reproductively separated populations
29
Speciation vs hardy weinberg
- evolution in terms of speciation will not take place if the conditions under the hardy weinberg principle does not change
30
What three factors can cause speciation to occur?
- genetic drift in isolated population
- the founder effect of disproportionate allele frequencies in small populations
- natural selection
31
what is genetic drift?
- variations in allele frequencies in small population due to chance
(rather than as a result of selection pressure)
32
How does genetic drift lead to speciation?
cause populations to diverge genetically, potentially leading to reproductive isolation and the formation of new species.
33
what is meant by the founder effect?
- when a small number of individuals become isolated, forming a new population with a limited gene pool
- allele frequencies are not reflection of the original population
34
what are the two types of speciation?
allopatric speciation
sympatric speciation
35
what is it meant by allopatric speciation?
when two populations become geographically isolated
36
what is it meant by sympatric speciation?
when two populations within the same area become reproductively isolated
37
outline geographical isolation?
- a physical barrier such as a river or mountain separates two populations of the same species
38
name the potential isolation mechanisms in sympatric speciation?
- morphological isolation
- seasonal isolation
- behavioural isolation
- gametic isolation
- hybrid sterility
- hybrid inviability
39
what is morphological isolation?
- reproductive isolation of two populations due to the incompatibility of their reproductive systems
40
what is behavioural isolation?
- the reproductive isolation of two populations due to differences in their behaviour ( such as mating rituals)
41
describe seasonal isolation
- reproductive isolation of two populations due to differences in their breeding seasons
42
describe hybrid inviability
- post zygotic barrier
- successful fertilisation but embryo cannot develop into a living organism
43
what is hybrid sterility?
- the formation of sterile hybrid offspring from the reproduction of individuals of different species i.e mule
44
why may the reproduction of individuals of different species produce sterile offspring?
- the chromosome sets from each parent differ so are unable to pair up during meiosis
45
give an example of a sterile hybrid and a fertile hybrid
- sterile hybrid - mule
- fertile hybrid - wheat
46
what is gametic isolation?
- prezygotic barrier
- successful fertilisation does not occur.
47
what does darwins theory explain?
- how existing species have arisen through modification of ancestral species by natural selection
48
What is the concept of natural selection based on?
- production of large numbers of offspring showing variation
- in competition, there is a struggle for survival
- the selective advantage of certain hereditary features enable some individuals to survive
- offspring inherit
49
Natural selection structure for exam
- variation..... due to random mutation
- link to selective pressure
- selective advantage
- enable them to survive and reproduce
- Therefore pass on the advantageous alleles to the next generation
