Evolution Chapters 7-10 (Biology)

CLOCK IN

Genotype vs phenotype

genotype:

• pair of alleles that determine a characteristic

phenotype:

• Appearance of the characteristic resulting from a genotypes interaction with the environment

Discontinuous variation vs continuous variation

Discontinuous:

When only one gene is involved and results in only a small number of discrete phenotypes.

coloumn graph

Continuous:

phenotype of a particular gene has a RANGE of phenotypes, not just one or two.

Scatterplot / trendline

Polygenic

traits that show continuous variation are controlled by multiple genes

e.g: height

Gene pool

The range of genes and their alleles present in an interbreeding population

• must have the potential to be passed on to the next generation

How can allele frequencies within a gene pool change?

• Mutations

• Environmental pressures

Most mutations are detected and repaired by enzymes.

If they cannot be repaired, they fall into categories. What are these categories?

1. Neutral mutations

   1. Has no effect on survival

2. Beneficial mutations

   1. Increase the likelihood of survival

3. Harmful mutations

   1. Decrease the likelihood of survival

What happens if a mutation occurs on the germ line? (in sperm and egg cells)

• the mutation can be passed on to future generations

• if it occurs in a somantic cell, the mutation will only affect the individual (will not be passed on)

What are point mutations?

Mutations in genes involving the addition, deletion or alteration of a single base (hence point)

What are substitution mutations, and what do they do?

A substitution mutation is when one base is substituted for another base in a particular gene

They can cause:

1. Missense mutations, which cause a different amino acid to be coded into the polypeptide. Consequently, the resultant protein is a completely different shape and no longer functions

2. Silent Mutations - no change in amino acid, because of degeneracy (still codes for the same amino acid). e.g: CCA codes for glycine. Any change in its last base does nothing; degenerate

3. Nonsense Mutations - the substitution mutation creates a STOP codon. Therefore, wherever the mutation occured, the polypeptide chain is stopped and a partial protein is created, where it has no function.

What 2 types of Missense mutation are there?

1. Conservative

   1. The amino acid replaced has similar chemical properties to the original and has little to no effect on the function of the polypeptide made

2. Non-conservative

   1. Different chemical properties, unlikely to carry out original function.

What is a frameshift mutation?

• When a base is inserted or deleted.

• shifts the series of codons by one base

• creates a different amino acid sequence

• leads to a non-functional protein.

What are the 2 types of frameshift mutation, and what do they do?

1. Insertion

   1. extra base is added

   2. affects the protein production from the point of insertion

2. Deletion

   1. base is left out of the DNA sequence

   2. affects everything from the point of the mutation

What is a block mutation?

Mutations that affect large portions of chromosomes, typically multiple genes

What are the 5 types of Block Mutation?

1. Insertion

   1. one section of the chromosome breaks off, and attaches to a different chromosome, leads to trisomy (3 sets of chromosomes instead of 2)

2. Deletion

   1. removal of sections. often lethal

3. Duplication

   1. Replication of a section of the chromosome, resulting in multiple copies of the gene

4. Inversion

   1. two or more bases copied the wrong way around, hence different amino acid

5. Translocation

   1. Whole chromosomes or a segment is exchanged with another chromosome or segment. can cause cancer.

What is a karyotype and what is karyotyping?

• A karyotype is a prepared set of human chromosomes (e.g: 23 homologous series )

• Karyotyping is used to detect genetic chromosomal abnormalities.

  • e.g: in fetuses before birth, so that parents can make an informed choice.

What is aneuploidy? And what is a polyploidy?

Aneuploidy:

the presence of an abnormal number of chromosomes, either extra or missing.

Polyploidy:

When three or more sets of chromosomes

Natural vs artificial selection?

Natural:

• When selection of survival of an individual is achieved by the natural environment

Artificial:

• When humans choose which individuals mate and therefore produce offspring through artificial means (selective breeding)

remember:

selection does not generate variation, it acts on the variation that already exists in the population

What are the 6 things for the theory of modern evolution?

1. Variation

   1. varying genotypic combinations, which is inheritable.

   2. generated by mutations, meiosis, sexual reproduction, and gene flow

2. Reproduction

   1. leads to genetically similar offspring (identical for asexual)

3. Struggle for survival

   1. the number of potential offspring that parents can produce is always larger than the number that survive or the environment can support.

   2. only the fittest or individuals that are most adapted will survive long enough to reproduce

4. Environmental selection pressures

   1. individuals that compete successfully for resources will leave a much larger proportion of offspring.

   2. as environments change over time, those organisms with characteristics that suit the environment are most likely to survive and produce offspring

5. Chance effects

6. Divergence and speciation

   1. isolation leads to divergence of species.

What are the 4 things that cause variation (called morphs):

1. Mutations

   1. These produce genotypic and hence phenotypic differences between individuals

2. Meiosis

   1. This occurs through genetic recombination (independent assortment and crossing over)

3. Sexual reproduction

   1. fusion of gametes from two individuals

4. Gene flow

   1. genetic exchange resulting from the movement of individuals from one population to another.

What are the 5 key stages of natural selection (when asked “natural selection“)

1. Genetic variation

   1. differing genes in population

2. Overproduction

   1. produce more offspting than the environment can support (survival of the fittest)

3. Struggle to survive

   1. Selection pressures

4. Successful reproduction

   1. organisms with helpful traits live the longest.

5. Change in allelic frequency

What is an example of natural selection?

The Australian Blowfly

1. The major method of control was via insecticides, such as dieldrin

2. However, the evolution of insecticide resistance decreased the effectiveness of the insecticide. (RR = reistant, rr = highly sensitive, Rr = intermediary between the two)

theres also antibiotic resistance in bacteria.

• Decreases genetic diversity

Darwin’s Finches (natural selection)

• finches on neighbouring islands were closely related, yet seperate species

• each island had differing survivial pressures

• The finches adapted to suit their own islands, eventually becoming different species

• This is called adaptive radiation

• Their beaks differed from species to species, to adapt to the food available on their island (larger beaks = tougher barriers to get through)

dont need to know too many details tho

What is gene flow?

The transfer of alleles between populations through interbreeding.
• Introduces new alleles into a population's gene pool.
• Increases genetic variation within the receiving population.

Genetic Drift

the change in frequency of alleles from generation to generation by chance alone.

can lead to either the founder effect or the bottleneck effect.

• Decreases genetic diversity

What is the founder effect?

• When a population started with very few members

• genetic pool is very small

• variation is limited to the alleles that came from the original members of the population

• e.g: isolation on an island or smth like that

• Decreases genetic diversity

What is the bottleneck effect?

• When there is a severe reduction in population size due to an intense natural selection or disaster

• variation can be decreased significantly with the loss of some alleles

• Inbreeding severely decreases variation and makes offspring vulnerable to disease or environmental change

• Decreases genetic diversity

What is selective breeding?

(also called artificial selection)

A form of selection where humans actively choose which traits should be passed onto offspring.

Manipulation of the gene pool

2 examples of selective breeding?

• dairy cattle bred to produce more milk

• Crops - bred to produce higher-quality food

what are the 4 steps of selective breeding?

1. Determine the desired trait

2. interbreed parents who show that desired trait

3. select offspring with the best form of the trait, and interbreed them

4. Continue this process until the population reliably reproduces the desired trait

What are 2 detrimental effects of selective breeding?

1. Reducing resistance to environmental change

   1. Less genetic variation, then less alleles available to survive if there is a change to the environment

2. Reduces biodiversity

   1. Selective bred species replaced natural varieties.

What is a consequence of rapid genetic change

Antibiotic resistance in bacteria

• means the bacteria can survive in the presence of an antibiotic

can be caused by:

1. doctors over-prescribing antibiotics - more opportunities for bacteria to mutate

2. Increased use of antibiotics in livestock farmings - resistant bacteria can be passed on to humans.

Impression fossils

• When the fossil forms and hard parts leach out and leave a cast or space left behind

Mineralised fossils

• When minerals fill up the cast that is formed, and hardens

Trace fossils

• Preserved evidence of an animal’s activity, behaviour without containing parts of the organism

• e.g: footsteps

Mummified organisms (fossil)

• organisms that have been trapped in a substance under conditions that reduce decay

• e.g: Insects trapped in amber

What is the process of fossilization?

1. Organism dies and is buried quickly by sediments in an undisturbed area

2. Oxygen is excluded

3. The weight of sediment layers squeeze out water, increasing pressure and temperature

4. Hard parts leech out leaving a cast or space in the sediment, which is filled with minerals and hardened

5. If the space is not filled, an impression fossil is left behind

6. If the space is filled later with foreign material, a cast is formed

7. The filled space is a mould of the organism

8. The sediment is buried by many layers. Pressure and temperature is exerted to form rock

What is relative dating?

• dating the absolute age of rock layers above and below the layer containing the fossil

• Depends on stratification (the formation of layers in sedimentary rocks)

  • just extra info to know:

    • Principle of faunal succession: higher rocks = younger

    • Complexity of fossils increase from lower layers to higher layers

What are index fossils?

• Index fossils are fossils that have already been dated.

• they give evidence of the relative age of fossils from different locations

• Abundant, widespread

What is absolute dating / radiometric dating?

• dating a fossil directly to determine its absolute age

• based on the principle that radioactive elements decay at a constant rate

What is Radiocarbon dating? (absolute dating through C dating.)

• Calculating the amount of decay of ¹⁴C based on its half life

• When an organism dies, its ¹⁴C disintegrates to ¹⁴N

• The half life of ¹⁴C is approx 5700 ± 40

• the amount of ¹⁴C is measured and compared to the amount of ¹²C in the rock

• limited to samples not older than 50 000 years old

• 
  

What is potassium/argon dating?

• used to date fossils up to billion of years old

• ⁴⁰K has a much longer half life than ¹⁴C

• ⁴⁰K is released from volanic rocks and decays into the gas ⁴⁰Ar

• the proportion of ⁴⁰K and ⁴⁰Ar are compared to calculate the age of the volcanic rock

• decay curve is the same as radiocarbon dating, but the x axis / time frame is much longer

Definition of species?

• A population where where members have the potential to interbreed in nature and produce fertile offspring.

• Organisms should look alike, should be able to interbreed and produce fertile offspring

Prezygotic vs Postzygotic

Prezygotic:

• pre-reproduction (before egg and sperm meet)

Postzygotic:

• post-reproduction (after egg and sperm meet)

What are the 5 prezygotic barriers?

1. Mechanical isolation

   1. Caused by structural differences of genitalia of species

2. Gametic isolation

   1. Sperm and egg can no longer fuse

3. Behavioural isolation

   1. Differences in behaviour. e.g: mating behaviours could be incompatible

4. Temporal isolation

   1. Breeding occurring at different times

5. Geographical isolation

   1. When 2 species have developed different ecological requirements (e.g: diff habitats)

What are 2 Postzygotic barriers that impede mating?

1. Reduced hybrid viability

   1. impaired development

2. Reduced hybrid fertility (sterility)

   1. When an offspring is infertile or die because of chromosomal or gene incompatiblity.

   2. e.g: horse + donkey = infertile mule

What is speciation generally?

Speciation is the division of one species into two new species

Usually caused by physical isolation (genetic drift and accumulation of genetic differences).

Which leads to divergent evolution (results in the accumulation of differences in the isolated populations)

leads to reproductive isolation (prevents gene flow between species)

Allopatric speciation vs Sympatric speciation

Allopatric speciation:

• Involves the separation of individuals in a population by a geographic barrier that inhibits migration and therefore reproduction between the 2 populations.

Sympatric speciation:

• Involves separation of 2 different species by a barrier that is not geographical

Steps of Allopatric speciation?

1. A physical barrier separates an ancestral population into two isolated populations. There is no gene flow.

2. Each environment presents different selection pressures. Random mutations independently introduce new alleles into each gene pool.

3. Individuals with phenotypes best suited to their specific environment have a selective advantage, surviving and reproducing to pass on their advantageous alleles.

4. Over generations, allele frequencies shift and the populations undergo genetic divergence.

5. Accumulated genetic differences lead to reproductive isolation.

6. If brought back together, and they can no longer interbreed to produce fertile offspring, then two distinct species have formed.

Steps of Sympatric speciation

1. A population inhabits the same geographic area with no physical barriers. A polymorphism (or difference in microhabitat selection, behavior, or flowering time) arises within the ancestral population.

2. Populations become reproductively or temporally isolated. Gene flow between the two groups is significantly reduced or ceases.

3. Each group experiences different selection pressures and accumulates distinct random mutations.

4. Over generations, allele frequencies shift independently, leading to genetic divergence.

5. Accumulated genetic differences prevent individuals from interbreeding

6. They can no longer produce fertile offspring, and reproductive isolation has occurred

7. Two distinct species have formed.

What are 2 examples of how sympatric speciation can occur?

1. Dietary changes

2. Changes in hours of activity (nocturnal vs diurnal)

Howea palms on Lord Howe Island (required example of sympatric speciation)

• There are 4 different species of Howea palms on the island, two of which have diverged by sympatric evolution

• These 2 palms have undergone sympatric evolution due to differences in soil composition.

• The soil preferences caused a phenological shift in the flowering times of the two species

• Because they flower at completely different times on their respective soil types, enough reproductive isolation was introduced to disrupt random mating between the two

What is meant when two species are homologous? (Pentadactyl limb)

• Structures are fundamentally similar, suggesting a common ancestry

• Provides evidence that the organisms have diverged from that common ancestor over time, this is called divergent evolution.

• Difference selection pressures caused different cariants to be selected for.

• If body parts are SIMILAR, but not related:

  • due to living in similar environments

  • similar variants which are selected for

What is a Vestigial structure?

• A reduced, non-functional structure inherited from a common ancestor.

• se.g: appendix

How do changes in DNA link to relatedness?

• Changes in nucleotide sequences are caused by mutations

• The more differences in the sequence, the more time has passed since the two species diverged from their common ancestor

How do changes in amino acid sequences link to relatedness?

• Changes in nucleotide sequences via mutations affect the sequences of amino acids

• However, some mutations are silent mutations (degeneracy) and do not affect the amino acid sequence

• Differences in amino acids accumulate more slowly than differences in nucleotide sequences

What are the three types of substitution in amino acids (becuz of point mutations in amino acids)

1. Conservative substitution

2. Semi-conservative substitution

3. Non-conservative substitution

What is conservative substitution?

• When the original amino acid is substituted for an amino acid with SIMILAR properties.

• Hence, little to no change in the protein.

What is semi-conservative substitution?

• When the substituted amino acid has a similar shape but different biochemical properties

• Could lead to changes in protein structure and function

What is non-conservative substitution?

• When the substituted amino acid is different from the original in terms of structure AND biochemical properties.

• Leads to a major change in the protein

What are genetic linkage groups and how can they provide evidence for common ancestry?

What:

• Genetic linkage groups are groups of genetic loci close together on the same chromosome; therefore, the genes rarely segregate.

How:

• The linkage groups are compared with other species to see if they are also linked

• If they are, it suggests that they share a common ancestor.

What is the principle of the molecular clock?

• The rate of base substitution or accumulation of mutations in DNA can be used to estimate how long ago two organisms diverged from one another

• It is based on the hypothesis that changes in DNA and proteins are CONSTANT over evolutionary time (and across different lineages) - the mutation rate.

What are 2 limitations of molecular clocks?

1. Sections of DNA mutate at different rates than others, therefore the clock cannot be applied to all organisms.

2. In order for genetic mutations to occur at a constant rate, they need to be neutral or not be affected by natural selection.

   1. Any regions that code for a specific phenotype are under natural selection and will be affected by outside selection pressures.

   2. Thus, the mutation rate of proteins and protein-coding DNA will not be constant.

How can mitochondria DNA (mtDNA) be used for molecular clocks? (change later)

• Unlike nuclear DNA, mtDNA doesn’t have repair mechanisms in response to mutations

• Therefore, the mutation rate is higher in mtDNA.

• This means it acts as a molecular clock for closely related species (whereas nuclear DNA is used to compare older lineages)

• It is easier to obtain larger amounts of mtDNA, because cells contain multiple mitochondria

• There is no crossing over and recombination of mtDNA or mixing of alleles from parents, because it is passed maternally

• Variation in human mtDNA can indicate waves of migration

• 
  

What is DNA hybridization?

• Involves bringing together the single stranded DNA of one organism with the single stranded DNA of another organism.

• Complementary base pairs pair up, and hybridization has occured

• The amount of complementary base pairing indicates how closely related the species are

• (extra note: heat is used to determine how much pairing has occured, the more heat = more complementary base pairs (H bonds))

What is DNA sequencing?

• DNA sequencing enables a biologist to determine the base sequence of specific genes.

• DNA sequencing data can be used to discover evolutionary relationships as well.

Process

• Uses a similar method to PCR.

• The DNA to be sequenced, nucleotides, primers, and DNA polymerase are mixed together.

• Only single primers are added, as well as "end nucleotides" that have been tagged with a different coloured fluorescent marker.

• When DNA polymerase begins, it will incorporate "normal nucleotides" and then a labelled "end nucleotide", which stops the sequencing process.

• This is repeated over and over again, eventually leaving the tube made up of a range of different-sized fragments all ending in a coloured base.

• Separation by gel electrophoresis enables the base sequence to be determined.

What is phylogeny? (phylogenetic trees)

• The pattern of how organisms are related through evolutionary descent from a common ancestor

What do phylogenetic trees represent? (just know how to interpret one tbf)

• Represents hypotheses about the evolutionary relationships among a group of organisms

• orgnaises species into nested groups based on shared derived traits

What do transitional fossils do?

• Transitional fossils represent the intermediate stages of evolution between distinctly separate species

What are 3 distinctive features of primates?

1. Hands with opposable thumbs (grasping)

2. Nails rather than claws (exposed fingertips for sensitivity)

3. Large eyes pointing forward (depth perception)

Differentiate between Primates, hominoids, hominids, and hominins (fix - need the specific distinctions of what each is.)

Primates:

• all moneys, lesser apes, great apes, and humans

Hominoids:

• lesser apes, great apes and humans (no monkeys)

Hominids:

• all modern and extinct great apes + humans

Hominins:

• modern humans, extinct human species and all our immediate ancestors.

What are 3 characteristics of hominoids?

• absence of a tail

• relatively long upper limbs

• mobile shoulder joints

• 
  

What are 3 features of a human? (lowk common sense but still)

• bipedal

• large brains

• narrower and deep pelvis

What are 3 characteristics of early hominins?

• Curvature of the spine to better bear weight while standing

• the position of the foramen magnum at the base of the skull

• A larger and cranial capacity (aka larger skull size)

Distinctive features of the australopithecines? (3 + bipedality)

• fully bipedal, with longer arms in comparison to the legs

• Smaller brain that humans

• teeth reduced in size, and faces large and projecting

3 distinctive features of the homo.

• gracile

• reduced brow ridge

• more vertical face

What is the difference between the 3 hypotheses for human populations?

• The ‘out of Africa‘ model suggests that homo sapiens evolved IN Africa, THEN migrated out into the world

• The multiregional evolution model suggests that homo erectus populations migrated out of Africa, THEN evolved separately into homo sapiens.

• The assimilation model suggests that homo erectus populations migrated out of Africa, AND homo sapiens evolved in Africa, and when they moved out, they interbred with those that have already left.

Why do we use mtDNA for looking at evidence for migration?

• Comes from maternal lineage - no recombination, like what occurs in nuclear DNA.

• Higher mutation rate, because it does not have repair mechanisms

• Contains smaller amounts of DNA

• Takes longer to degrade than nuclear DNA

Compare Bottleneck and Founder effect

The bottleneck effect is due to a random event that abruptly decreases population numbers, reducing alleles in the population

The founder effect is when a small group leaves the parental population, and inbreeding occurs, with the new population not representative of the parental population’s alleles.

As the new populations have low genetic diversity, they are more at risk of extinction. If conditions were to change, it is unlikely they will have individuals that have favourable allelesto enable survival

How can antigenic shift affect a population?

A previously unknown virus occurs when 2 or more viruses join creating antigens that

are not complementary to any vaccines/memory cells.

As no-one has immunity, the virus has

hosts that can readily transmit the virus before the adaptive response can suppress it.

“what would determine whether a NEW SPECIES has arisen?“

• Cannot interbreed

• Cannot produce fertile offspring / REPRODUCTIVE ISOLATION.

DEFINE mammals, primates, hominoids, hominins.

• Mammals: Animals with fur/hair and mammary glands (produce milk).

• Primates: Mammals with opposable thumbs and forward-facing eyes (3D vision).

• Hominoids: Primates with no tail (all apes and humans).

• Hominins: Hominoids that walk upright on two legs (obligate bipedalism).

What are the causes for the change in allelic frequency in a populations gene pool?

environmental selection pressures, genetic drift, gene flow, mutations as the source of new alleles

What do u gotta talk about bout phenotypes from mutations?

talk about "selective advantage" and that they will "survive, reproduce and pass on their genes"

What are conseuqences to a gene pool if there is no gene flow

• Loss of genetic diversity

• Increased interbreeding