Continuity Of Life Revison

Question 1

How long has life existed on Earth?

Answer 1

Life has existed on Earth for approximately 3.5 billion years and has changed and diversified over time

Question 2

Distinguish between microevolution and macroevolution

Answer 2

Microevolution- changes of allele frequencies within a species or population over a short period of time. Eg- bacteria

Macroevolution- major evolutionary change, especially with regard to the evolution of whole taxonomic groups over long periods of time through the accumulation of microevolutionary change. Eg. Evolution of horses

Question 3

List barriers to gene flow, both geographical and others.

Answer 3

• Rivers
• Mountain ranges
• Oceans
• Lakes
• Canyons
• Deserts
• Roads

Question 4

Describe how the process of natural selection leads to changes in the characteristics of a population.

Answer 4

The process by which forms of life having traits that better enable them to adapt to specific environmental pressures (predators, change in climate, competition for food or mates) will tend to survive and reproduce in greater numbers than others of their kind thus ensuring the perpetuation of those favourable traits in succeeding generations.

Question 5

List selective pressures that can lead to change in the gene pool or extinction of a species

Answer 5

1. Resource availability – Presence of sufficient food, habitat (shelter / territory) and mates
2. Environmental conditions – Temperature, weather conditions or geographical access
3. Biological factors – Predators and pathogens (diseases)

Question 6

Why are mutations referred to as the ultimate source of variation?

Answer 6

Mutation is the ultimate source of genetic variation as it introduces new alleles into a population.

Question 7

Describe using examples the process of artificial selection.

Answer 7

1. Identify the desirable traits
2. Choose the parents with the desired traits
3. The selected parents are then crossbred to produce offspring that inherit the desirable traits.
4. The offspring are then evaluated, and the individuals with the most desirable traits are selected as parents for the next generation.
5. Repeat the process: The process of selecting and breeding the best offspring is repeated over several generations until the desired trait is consistently present in the population.

Examples: Any modern agricultural product - Sheep, cows, fruit, vegetables, grains

Question 8

What type of characteristics are humans looking to enhance through the use of artificial selection?

Answer 8

1. Disease resistance
2. Faster growth rate
3. Improved product quality
4. Improved yield
5. Tolerance to adverse conditions

Question 9

Define the term gene pool.

Answer 9

The sum of the alleles in a given population.

Question 10

Define the term selection pressure and list some examples

Answer 10

Any feature of the environment that reduces (or increases) the fitness of a particular phenotype in a population of organisms.

Examples:
– Competition for food, mates, space
– Predators, climate, food sources

Question 11

Explain how natural selection can lead to changes in the allele frequency of a gene pool.

Answer 11

Natural selection will favor genes that are more suited to their environment and become more exclusive in the gene pool over time, which can happen when the environment changes, or the species migrate.

Question 12

Explain how the founder effect can lead to changes in the allele frequency of a gene pool.

Answer 12

• A small group of individuals splits off to start a new population
• More likely to be affected by genetic drift due to small population size
• The alleles in the founder population may not be representative of the original population
• Once the population has increased the gene pool is still representative of the founder population not the original population

Question 13

Explain how population bottlenecks can lead to changes in the allele frequency of a gene pool.

Answer 13

• A sudden drastic reduction in population size
• Drought, flood, fire, hunting, progressive environmental change
• Surviving individuals constitute a random genetic sample of the original population (some alleles are lost)
• Small populations are more susceptible to genetic drift
• Population numbers may recover but the gene pool will remain small

Question 14

Explain how random genetic drift can lead to changes in the allele frequency of a gene pool.

Answer 14

• Is a mechanism of evolution in which allele frequencies of a population change over generations due to chance events (eg death of an individual) not selection
• Occurs in all populations, but its effects are strongest in small populations
• May result in the loss of some alleles (including beneficial ones) and the fixation (100% frequency) of other alleles
• The alleles in the offspring are a sample of those in the parents, and chance has a role in determining whether a given individual survives and reproduces.

Question 15

Define the term allopatric speciation.

Answer 15

Allopatric speciation occurs when two or more populations are prevented from breeding by geographical separation.

Question 16

Explain how allopatric speciation occurs.

Answer 16

Step 1 - Variation:
- All populations show different degrees of variation between individuals both phenotypically and genotypically.

Step 2 - Isolation
- A population gets split into two by a geographic barrier
- Interbreeding (gene flow) between the two populations stops.

Step 3 - Selection
- Different selection pressures- natural selection favours different characteristics in each sub-population
- Therefore gene pools change independently of eachother
- Because there is no gene flow between the two populations mutations that arise in one population will not appear in the other (= greater variation)
- The smaller the population the faster evolution occurs

Step 4 – Reproductive Isolation
- Eventually the two populations accumulate enough genetic differences that they can no longer interbreed, or produce fertile offspring (= different species).

Question 17

Explain how fossils provide evidence for evolution

Answer 17

1. Shows changes in structure over time
2. Organisms in the fossil record have become more complex over time. More recent (younger fossils) are more similar to organisms living today.
3. The variety of fossils increases in the upper more recent layers of rock
4. No fossil record exists of any modern living plants or animals. This suggests that the organisms that are found as fossils either became extinct or evolved into species currently living.
5. Missing links – the common ancestors

Question 18

Explain how comparative anatomy - homologous structures provide evidence for evolution (divergent evolution).

Answer 18

Organs with similar structure but not necessarily similar function. Eg Pentadactyl limbs (5 digits), 2 bones in forearm. Suggests they all had a common ancestor with that structure. The pentadactyl limb structure is not necessarily the best design for each of the varied modes of locomotion. Only organisms with the a common ancestor can have the same basic structure (structures appear via mutation).

Question 19

Explain how comparative anatomy - analogous structures provide evidence for evolution (convergent evolution).

Answer 19

Process whereby organisms not closely related independently evolve similar traits as a result of having to adapt to similar environments or ecological niches. Different structures with the same function.

Question 20

Explain how comparative embryology provides evidence for evolution

Answer 20

Some vertebrates possess traits that are present in the embryos but are not present in adults. These traits had a function in the ancestors of the organism but not present in the adult because they do not have a function in the adult stage of these organisms. Suggests they all share a common ancestor.

Question 21

Explain how vestigial organs provide evidence for evolution

Answer 21

A structure that, during the course of evolution, has been reduced in size or has lost its function. Structure that is no longer functional. Structure had a function in ancestors. Shows evidence of relationships among organisms (evolved from organisms where the structure had a function).

Question 22

Explain how comparative biochemistry (genomics) provide evidence for evolution

Answer 22

The study and comparison of the genome sequences of different species. Enables identification of genes that are conserved or common among species, as well as genes that give each organism its unique characteristics.

Question 23

Explain how comparative biochemistry can be used to create a phylogenetic tree

Answer 23

• A tree diagram representing the evolutionary relationship between organisms which is shown through the branching of the tree
• The most recent descendent species are at the tips of branches
• Common ancestors are at base of the tree
• Branching point represent time when each branch last shared a common ancestor
• Branch length represents divergence time
• Closely related species will be grouped in same part of tree

Question 24

Why does a reduction to the gene pool lead to increased risk of extinction?

Answer 24

Genetic diversity allows a population to effectively evolve and adapt through natural selection. With low genetic diversity, a species could easily be wiped out. Low biodiversity = low ecosystem stability. Alleles lost from the gene pool decrease biodiversity.

Question 25

Define the term bioinformatics

Answer 25

Bioinformatics- The science of collecting and analysing large sets of biological data such as (AA sequences or nucleotide sequences) using computer modelling. Compare DNA, genes and protein sequences within a species or between different species.