chapter 9 (evolution)

Question 1

genetic diversity

Answer 1

• the variation in genetic makeup or allele within a population
• larger, more diverse pool with a greater variety of alleles will lead to a greater number of genotypes and phenotypes therefore resulting in a greater genetic diversity.

Question 2

point mutation

Answer 2

• a mutation that alters a single nucleotide in a DNA sequence

Question 3

silent mutation (substitution)

Answer 3

• DNA triplet codes for the same amino acid
• single base substitution
• may have no effect

Question 4

missense mutation (substitution)

Answer 4

• codes for a different amino acid, alters polypeptide
• could alter functioning
• lesser impact on the end/non-critical part
• greater impact in the middle, may cause protein to be non-functional

Question 5

nonsense mutation (substitution)

Answer 5

• ends translation/mutated triplet and becomes stop codon
• stops protein production
• most dangerous

Question 6

frameshift mutation (insertion)

Answer 6

• single base substitution (major affect)
• codes for different amino acid
• all codons are shifted one spot

Question 7

frameshift mutation (deletion)

Answer 7

• reading frame is shifted from deletions
• all triplets downstream will code for different amino acids
• proteins become non-functional

Question 8

block mutation

Answer 8

a mutation that affects a large chunk of DNA, or a entire gene

Question 9

duplication

Answer 9

• large or small section is copied
• increase in trinucleotide repeats
• results in the addition of many more amino acids in resulting protein
• protein function can be altered
• (e.g Huntington’s Disease)

Question 10

deletion

Answer 10

• portion is removed or lost
• chromosomes breaks in 2 places and rejoins leaving a piece out
• large deletions are usually lethal
• smaller deletions lead to genetic disorders

Question 11

translocation

Answer 11

• segments of 2 chromosomes are exchanged, attaches to different non-homologous chromosomes
• if parts are lost it has no effect on carrier but can affect the gametes
• zygote receiving extra copy of DNA
• (e.g Down Syndrome)

Question 12

inversion

Answer 12

• segment is removed then replaced in the reverse order (flipped)
• depending on where break occurs
• if in coding or promoter region gene function is lost.

Question 13

environmental selection pressures

Answer 13

predation, disease, competition, climate change

Question 14

four conditions of natural selection

Answer 14

• variation: individuals population vary genetically which leads to phenotypic differences
• selection pressure: an environmental selection pressure impacts the survivability of organisms within a population and their ability to reproduce
• selective advantages: individuals with phenotypes that are fitter or more advantageous under the environmental selection pressure are conferred a selective advantage allowing them to survive and reproduce more successfully
• heritability: the advantageous trait must be heritable, allowing it to be passed on from the parents to their offspring therefore over time the frequency of the advantageous allele will increase.

Question 15

Darwin’s observations

Answer 15

• 1: there is a phenotypic variation within species
• 2: offspring tend to inherit traits of their parents
• 3: species produce more offspring then required to replace themselves
• 4: there is a struggle to survive.

Question 16

Darwin’s inferences

Answer 16

• A. Individuals whose traits give them more chance to survive and reproduce leave more offspring than other individuals
• B. The unequal chance of reproduction will lead to accumulation of favourable traits in the population over generations.

Question 17

sexual selection (female choice)

Answer 17

• who reproduces at the expense of survival
• males fight with each other in order the get the right to mate with all the females

Question 18

bottleneck effect

Answer 18

• The bottleneck effect occurs when a large portion of a population is wiped out by a random event such as a natural disaster
• New generation will depend on remaining alleles
• decreases genetic diversity

Question 19

founder effect

Answer 19

• The founder effect occurs when a small unrepresentative sample of individuals separates from a larger population to colonise a new region and start a new population
• decreases genetic diversity

Question 20

immigration

Answer 20

• the movement into a population
• alleles are added to the gene pool of a population
• increase genetic diversity

Question 21

emigration

Answer 21

• the movement out of a population
• alleles are removed from the gene pool of a population
• decrease genetic diversity

Question 22

interbreeding

Answer 22

• when two individuals living in different populations mate and have offspring
• increase genetic diversity

Question 23

Reductions in genetic diversity have two major risks

Answer 23

• Inbreeding: this keeps harmful alleles in the gene pool
• Lower adaptive potential: populations become vulnerable to new selection pressures that could challenge and potentially wipe out the entire population due to the absence of advantageous alleles.

Question 24

Speciation

Answer 24

• is the process by which populations genetically diverge until they become distinct species
• Individuals are recognised as different species if they can no longer interbreed with one another to produce viable and fertile offspring.

Question 25

Hybrids

Answer 25

• They can all mate and produce offspring, but the offspring are infertile
  e.g Horse and Donkey create a Mule

Question 26

isolating mechanisms (pre-reproductive)

Answer 26

• Geographical - individuals may not be able to interact with each other due to separation by barriers (e.g. body of water)
• Ecological - individuals may inhabit different ecological niches or habitats so they do not interact with each other
• Temporal - the time of the day or year when individuals are ready to breed may differ
• Behavioural - the type of mating behaviours, such as mating call, of individuals may vary.
• Structural - the physical characteristics of individuals may drastically vary, physically preventing breeding.

Question 27

isolating mechanisms (post reproductive)

Answer 27

• Gamete mortality - the sperm may be unable to penetrate the ovum for fertilisation
• Zygote mortality - fertilisation may occur and a zygote may be formed, however, it will not survive
• Hybrid sterility - a viable offspring may be formed and may survive until adulthood, but will not be fertile.

Question 28

allopatric speciation

Answer 28

• the geographic separation of a population from a parent population resulting in the formation of a new species
• 1 A geographical barrier separates a population preventing gene flow.
• 2 Different selection pressures act upon each population favouring different phenotypes and allowing for genetic differences to accumulate.
• 3 Eventually, sufficient genetic differences accumulate so that the two populations can no longer interbreed to produce viable and fertile offspring,
• (e.g galapagos finches, due to all bring in different ecological niches on the different islands they were all faced with different selection pressures, experienced adaptive radiation)

Question 29

sympatric speciation

Answer 29

• the divergence of a species from an original species without the presence of a geographical barrier sympatric, speciation occurs within populations sharing the same geographical location
• different selection pressures act on different phenotypes within a population causing them diverge and create a new species
• also arise from genetic abnormalities that occur during gamete formation resulting in a different number of chromosomes compared to the parents.
• (e.g howea palms, different PH levels were the reason for their speciation, these changes altered their flowering time and therefore they could no longer interbreed)

Question 30

selective breeding

Answer 30

• the changing of a population’s gene pool due to humans altering the breeding behaviour of animals and plants to develop a selected trait

Question 31

the requirements for selective breeding

Answer 31

• Variation: individuals in a population vary genetically, which leads to phenotypic differences
• Selection pressure: direct human intervention places an artificial selection pressure upon a population of individuals only allowing certain individuals with desirable traits to breed together
• Heritability: the trait selected must be heritable allowing it to be passed on from the parents to their offspring.

Question 32

effect of selective breeding on genetic diversity

Answer 32

• restricting breeding to these individuals the generational increase in the frequency of the selected allele will decrease genetic diversity as the phenotypes of the population are driven towards a specific allele

Question 33

natural selection

Answer 33

• population is in the wild, depends on selection by the environment
• selecting agents: climate changes, competition, food shortages, mate availability, predator abundance, pollution

Question 34

artificial selection

Answer 34

• population is in captivity, occurs when humans deliberately select particular pants or animals to breed for a specific trait
• select breeds that would not be genetically fit in the wild

Question 35

antibiotic resistance

Answer 35

• bacteria with resistance to a particular antibiotic are present confer a selective advantage allowing them to continue leaving and replicating increasing the allele frequency for antibiotic resistance

Question 36

antigenic drift

Answer 36

• involves small and gradual changes in the genes encoding for viral surface antigens
• as mutations continue to accumulate a new subtype can firm which will no longer be recognised

Question 37

antigenic shift

Answer 37

• involves sudden and significant changes in the genes encoding for viral surface antigens
• two or more different strains of a virus combine
• natural immunity is uncommon making it extremely infectious