6.1.2 - Patterns Of Inheritance (set B - Evolution + Speciation)

Question 1

Define gene pool and allele frequency?

Answer 1

The sum total of all the genes in a population at any given time

• allele frequency - the relative frequency of a particular allele in a population

Question 2

Outline and explain the Hardy-Weinberg principle states and its use?

Answer 2

In a stable population with no disturbing factors, the allele frequency will remain constant from one generation to the next and there will be no evolution

• used to predict how gene frequencies change from generation to generation and the genetic variation of a population

Question 3

What assumptions does the hardy-Weinberg principe take into account - give 4?

Answer 3

• population is large and isolated
• random mating
• no mutations
• no selection pressure

conditions never really occur in natural environments

Question 4

Give 5 factors which affect evolution and explain how they do so?

Answer 4

• mutations
• sexual selection
• gene flow
• genetic drift
• natural selection

all of these lead to changes in frequency of alleles within a population - thus affecting evolution

Question 5

Explain how mutations lead to evolution?

Answer 5

Mutation leads to existence and formation of new alleles which leads to genetic variation

Question 6

Explain how sexual selection leads to evolution?

Answer 6

Leads to increase in frequency of alleles which code for characteristics that improve mating success

Question 7

Explain how gene flow leads to evolution?

Answer 7

Gene flow is movement of alleles between populations - immigration and emigration results in changes of allele frequency within a population

Question 8

Explain what genetic drift is and how it leads to evolution?

Answer 8

• occurs in small populations
• change in allele frequency (due to random mutation) which is more likely to increase in number (in a smaller population than a large) due to smaller number of alleles present in gene pool

Question 9

Explain how natural selection leads to evolution?

Answer 9

Leads to increase in number of individuals that have characteristics that improve chances of survival - reproduction rates increases amongst these individuals, so frequency of alleles coding for these characteristics increases also

• explains how changes in environment can lead to evolution

Question 10

Explain the significance of a large population and its role with selection pressures?

Answer 10

Large populations have a more genetically diverse gene pool (due to presence of many different genes and alleles) - genetic diversity leads to variation within a population, which is essential for process of natural selection

• population will better be able to adapt to selection pressures (disease,changing environment,humans ext)

Question 11

Explain why small populations can be bad for survival of a species?

Answer 11

Small populations have limited genetic diversity - cannot adapt to changes as easily (more likely to become extinct eg by a pathogen wiping out whole population)

limiting factors are those that limit/decrease size of a population

Question 12

Give 2 types of limiting factors which impact population size - explain them and give examples?

Answer 12

Density-dependent factors - dependent on population size - include competition, communicable disease and predation

Density-independent factors - affect populations of all sizes in the same way - include climate change, natural disasters and human actives like deforestation

Question 13

Explain what a population bottleneck is and its effect?

Answer 13

Population bottlenecks - are large reductions in population size which lasts for at least one generation (positive factor of bottleneck is that a beneficial mutation will have much greater impact, leading to to quicker development of a new species)

• gene pool and genetic diversity is greatly reduced (genetic diversity takes thousands of years to develop through accumulation of mutations - therefore a significant impact on population)

Question 14

Explain and define the founder effect?

Answer 14

Small populations can arise due to establishment of new colonies by a few isolated individuals

• extreme example of genetic drift
• small populations have much smaller gene pools and display less genetic variation

Question 15

Explain stabilising selection - give an example?

Answer 15

• type of natural selection
• favours individuals with average or moderate phenotypes (positive selection) and selects against extreme phenotypes
• for example infants with an intermediate weight have a higher chance of survival than those who are very small or very large

leads to reduction in frequency of alleles at the extremes and increases ‘average’

Question 16

Explain directional selection?

Answer 16

• type of natural selection
• occurs when there is a change in the environment and the normal (most common) phenotype is no longer the most advantageous
• organisms with more extreme (less common) phenotypes are positively selected

allele frequency shifts towards extreme phenotypes - evolution occurs

Question 17

Outline and explain an example of directional selection - use the peppered moths?

Answer 17

Peppered moths during Industrial Revolution - lots of smoke and soot released which made the bark black (moths were originally light coloured to camouflage with lighter bark)

• there were always a few darker moths present due to variation (allele frequency was maintained though due to lack of camouflage so darker moths were eaten)
• light coloured moths now more visible and eaten so darker moths which were camouflaged survived - led to shift in allele frequency to an extreme phenotype (directional selection)

Question 18

Explain distruptive selection?

Answer 18

• type of natural selection
• this selection involves the extremes selected for and the norm selected against
• distribution of phenotypes show 2 distinct peaks on graphs
• relatively rare

Question 19

Give 3 types of natural selection?

Answer 19

• stabilising selection
• directional selection
• disruptive selection

Question 20

Define speciation?

Answer 20

The formation of new species through process of evolution - organisms of new species no longer able to interbreed to produce fertile offspring within original species

• caused by a number of events like isolation of members of a population and random mutations

Question 21

Outline 3 events that can lead to speciation?

Answer 21

• members of population become isolated and no longer interbreed with rest of the population - results in no gene flow between the 2 groups
• alleles within group continue to undergo random mutations - environment of each group may be different or change (resulting in different selection pressures) so different characteristics will be selected for and against
• accumulation of mutations and changes in allele frequency over many generations, leads to changes in phenotype (members become so different they can no longer interbreed and produce fertile offspring) - now reproductively isolated

Question 22

Give 2 types of speciation?

Answer 22

• allopatric speciation
• sympatric speciation

Question 23

Explain allopatric speciation?

Answer 23

• most common form of speciation
• **happens when members of a population are separated from rest by a physical barrier (river/sea) and are geographically isolated - each group experiences different environments and thus selection pressures, resulting in different physical adaptions **
• separation of small group leads to founder effect, leading to genetic drift

Question 24

Explain sympatric speciation?

Answer 24

happens when members of 2 different species interbreed, and produce fertile offspring - this hybrid is a new species (has different number of chromosomes to each parent - may no longer be able to breed with members of either parent population) - stops gene flow and reproductively isolates the hybrid organism

• less frequent that allopatric (more common in plants and occurs within populations that share habitat)

Question 25

Explain the different types of reproductive barriers?

Answer 25

The reproductive isolation can be either pre-zygotic or post-zygotic

• for example pre-zygotic prevents fertilisation and formation of a zygote

Question 26

Define polymorphic?

Answer 26

Displaying more than one distinct phenotype

Question 27

Explain artificial selection/selective breeding?

Answer 27

• fundamentally same as natural selection expect for nature of selection pressures applied
• individuals with desired characteristics are selected and interbred - offspring from this cross which best show the desired traits are then selected to breed, process is repeated over many generations
• results in changes to frequency of alleles within population and eventually speciation

Question 28

Outline the problems caused by interbreeding?

Answer 28

• limits the gene pool, so decreases genetic diversity which reduces the chances of a population of inbred organisms evolving and adapting to changes in their environment
• many genetic disorders caused by recessive alleles (cystic fibrosis) - closely related organisms are more genetically similar, more likely to have offspring which are homologous for these recessive traits

Question 29

Explain what seed banks are?

Answer 29

Keep seeds from both wid type and domesticated varieties - used to increase genetic diversity through outbreeding

• important genetic resource
• gene banks store biological samples (sperm and eggs)

Question 30

Explain the point of outbreeding?

Answer 30

Used to increase genetic diversity and combat the effects of inbreeding

• involves breeding unrelated or distantly related varieties - reduces the occurrence of homozygous recessives and increases potential to adapt to environmental change