AOS 5 - Biology - Adaptations

Define gene pools

Gene pools are the complete set of all genes and alleles present within a particular population or species

What is the importance of a diverse gene pool?

Larger gene pools will contain a variety of genes and alleles, leading to a greater number of genotypes and phenotypes resulting in increased genetic diversity

Define mutations

Mutations involve permanent changes to the DNA sequence of an individual

What factors cause mutations?

Radiation (UV (from sunlight), X-rays)

Infectious Agents (Viruses, Bacteria)

Chemicals (Carcinogens (cigarettes), Processed foods + preservatives, Cosmetics + cleaning products)

How can mutations be catergorised?

As advantageous, neutral or disadvantageous based on the mutation’s overall effect on the survivability of the individual.

Where do mutations need to occur to make them heritable?

They need to occur in an individual’s germline cells (cells that generate gametes (sex cells), not somatic cells (body cells) as gametes contain the genetic information that is passed on to the offspring.

What are point mutations?

These describe the changes to a single nucleotide.

What are the types of point mutations?

Substitution

• Silent (amino acid remains the same)

• Missense (different amino acid)

• Nonsense (introduces a premature stop codon, creating a termination sequence)

Frameshift Mutation

• Insertion (nucleotide added to the sequence)

• Deletion (nucleotide removed from the sequence)

What are block mutations? And the types of block mutations?

Involve changes to larger sections of DNA, potentially causing significant changes

• Deletion - removal of a section of DNA

• Duplication - replication of a section of DNA

• Inversion - reversal of a section of DNA

• Translocation - switching of two sections of DNA on different chromosomes

When do block mutations usually occur?

During the process of meiosis

Define aneuploidy

when an individual has either one extra or one too few chromosomes

Define polyploidy

when an individual has more than two sets of chromosomes

Define environmental selection pressures, and provide examples

factors within the environment that influence the survivability of a species.

Examples include predation, disease, competition, and climate change

What is natural selection?

A process in which organisms more suited to a particular environment are considered to have high genetic fitness due to the presence of their advantageous phenotypes

Overtime, because the fitter organisms have selective advantage they survive increasing the advantageous allele frequency in future populations

State the four conditions of Natural Selection

1. Variation

2. Selective pressure

3. Selective advantageous

4. Heritability

*discuss all four when explaining natural selection

What occurs at Variation?

Individuals in population vary genetically, which leads to phenotypic differences

What occurs at Selective Pressure?

An environmental selection pressure that impacts the survivability of organisms within a population and their ability to reproduce

What occurs at Selective advantageous?

Individuals with phenotypes that are fitter or more advantageous under the environmental selection pressure are given a selective advantage, allowing them to survive and reproduce

What occurs at Heritability?

The advantageous trait must be heritable, allowing it to be passed on from the parents ot their offspring. Therefore, over time, the frequency of the advantageous allele will increase

Define genetic variation

Differences in DNA sequences between individuals of the same species, leading to diverse traits/differences - this results from mutations, geneflow, sexual reproduction

How do selective pressure affect genetic diversity?

Selective pressures drive adaptations, and if a positive response is created, the frequency of advantageous traits will increase, at the expense of other disadvantages ones.

High genetic diversity increases the chance of possessing favourable alleles, aiding the species in surviving selection pressures.

Low genetic diversity exposes them to extinction due to the inability to adapt.

Define evolution

the change in genetic makeup of a population successive generations

define genetic drift

in response to random events, allele frequencies can change drastically and affect a population’s overall genetic diversity

What is the bottleneck effect?

• When a large portion of a population is wiped out by a random event (natural disaster)

• This decreases the population size, impacting allele frequencies - lower genetic diversity

What is the Founder effect?

• when a smal, unrepresentative sample of individuals seperate from the larger population, colonising in a new region

• The new populations genetic diversity is low

How does genetic drift reduce genetic diversity?

Through the random removal of alleles from the gene pool

It also increases the risk of inbreeding and lowers the adaptative potential

• Bottleneck reduces through random events

• Founder reduces through the establishment of a new population with a small un-representative sample

Define gene flow

The movement of alleles between different populations (either through migration or inbreeding)

Define immigration

When individuals enter a population, adding their alleles to the gene pool

Define emigration

Individuals exit a population, removing their alleles

Define a species

A group of individuals who are able to breed with eachother and produce viable offspring

Define speciation

The process by which populations genetically diverge until they become different species

→ this occurs when enough genetic differences have developed due to mutations, natural selection, gene flow and genetic drift

What are isolating mechanisms?

The pre-reproductive and post-reproductive mechanisms that prevent different species from interbreeding to produce fertile/viable offspring

What are the types of post reproductive mechanisms that isolate populations causing speciation?

• geographical

• ecological

• temporal

• behavioural

• structural

What are the types of pre-reproductive mechanisms that isolate populations causing speciation?

• gamete mortality

• zygote mortality

• hybrid sterility

Define allopatric speciation

involves the formation of new species as a result of a geographical barrier

How do geographical barriers cause the formation of new species?

A geographical barrier prevents gene flow, with different selection pressures causing genetic differences to develop until the two populations can no longer interbred

What is sympatric speciation?

Doesn’t rely on geographical barriers to prevent gene flow, it occurs within populations sharing the same locations where different selection pressures act on different phenotypes causing new species to develop.

Define selective breeding

When the selection pressure is human-induced, and there is a desired trait that humans are selecting for (or removing from the populations)

What are the requirements for selective breeding?

Variation: natural phenotypic variation within the population

Selection Pressures: the favourable trait is selected by humans, who they pressure and establish a breeding population with the trait-genetically controlled

Heritability: as the favourable trait is heritable, it will increase in allele frequency due to repeated selection reinforcements.

What is the main type of selective breeding, and the others?

Main: selecting for a trait you want

Others: selecting against the trait you want + selecting against the trait you don’t want

What are antimicrobial agents (examples, and role)

• Eg: antifungals, antivirals, antibiotics

• Play an important role in protecting against harmful pathogens, except new antimicrobial agents need to constantly created because pathogens are becoming better at resisting them

How is antibiotic resistance developed?

The formation of antibiotic-resistant bacteria can be attributed to the process of natural selection, where the exposure to antibiotics serves as an environmental selection pressure

Explain the process of natural selection in the context of developing antibiotic resistance

1. Variation - A population of bacteria has individuals that are resistant to an antibiotic, and those susceptible/sensitive to it

2. Selection pressure - exposure to the antibiotic acts as an environmental selection pressure

3. Selective advantage - this is given to the bacteria resistant to the antibiotic

4. Heritability - Bacteria resistant to the antibiotic are able to continue replicating and pass on the allele for resistance to other bacteria via bacterial conjugation, increasing it allele frequency

Do antibiotics cause bacterial resistance?

No. The evolution and development of this resistance is an example of natural selection, where this resistance to certain antibiotics already exists within the population, and the exposure to the antibiotics acts to highlight those resistant.

How is this variation in genes created that allows the resistance to antibiotics?

Mutations. Variation and the emergence of new alleles are largely caused by mutations. These can include:

• Inactivation (addition of a phosphate group to the antibiotic, reducing its ability to bind to bacterial ribosomes)

• Pumping out (increasing active efflux of drugs)

• Modification (changing the shape of the protein targeted by the antibiotic)

Are there any other factors that contribute to the development of antibiotic resistance?

• Inappropriate compliance with a treatment plan (patient not completing their course of antibiotics)

• Inappropriate use of antibiotics

• Widespread use of antibiotics in general = overexposure

Define antigenic drift

This involves small and gradual changes in the genes encoding for viral antigens (in the beginning, memory cells will still be able to recognise the virus, but if enough changes accumulate, they may not)

Define antigenic shift

This involves the sudden and significant changes to the genes encoding for viral antigens, commonly due to two or more different strains of a virus combing, meaning little immunity will exist.

List the key events in history of life on earth

1. Emergence of prokaryotes

2. Widespread photosynthesis

3. First eukaryotes

4. First multicellular organisms

5. The Cambrian Explosion

6. Animals on land

7. Mammals

8. Flowering plants

What is a fossil?

Sometimes, given the right set of conditions, the remains of a body can be preserved and form a fossil - all fossils both discovered and undiscovered are referred to as the fossil record

Outline the process of fossilisation

1. A body/dinosaur dies in a river

2. The body is covered with sediment, the soft tissues decompose and the hard body structures become fossilised by permineralization

3. The sedimentary layers accumulate and the resultant pressure forms sedimentary rock

4. The earth’s movements raise the layers of the rocks to the surface

5. The rock erodes, exposing the fossilised body structures

Define trace fossils

Trace fossils are indirect evidence of an organisms existence, such as their footprints or nests

What are the conditions that increase the likelihood of fossilisation?

• Physical protection from decomposers/scavengers (fungi, bacteria)

• Areas of rapid sediment accumulation

• Constant cool temperatures - slows down decomposition

• Low oxygen availability and light exposure - slows down decomposition

Define relative dating

Relative dating involves estimating a fossil’s age by comparing it to the known age of other fossils and/or rocks.

The law of succession states that the closer to the surface a fossil is, the younger it is, due to sedimentary rock being laid in layers based on time.

What are index fossils?

Index fossils are fossils that are widespread, physically distinctive, existed for a short period of time and have a know age - they and be used to determine the relative age of another fossil in the same layer, or below or above. Trilobites and ammonoids are good examples.

Define transitional fossils

Transitional fossils show traits that are common to both its ancestral group and its descendant group, showing certain features that have changed and evolved over time

What is absolute dating and what aer radioisotops?

• Involves calculating the age of a fossil in years

• An example is radioactive dating

• Radiometric dating involves measuring amounts of radioisotopes and their products

• A radioisotope is an unstable form of an element, that will spontaneously break down into a more stable product (eg carbon 14 → nitrogen 14)

Define what a ‘half-life’ is

The half-life of a particular radioisotope is the amount of time before half the original mass is broken down into its products

How does radioactive dating work?

It works by comparing the ratio of a radioisotope to its broken-down product - using the known half-life of the radioisotope, we can calculate how old the object we are dating is

What is comparative anatomy, and what does it involve?

• Comparative anatomy is the study of similarities and differences in the structural morphology of fossils

• It includes homologous, analogous and vestigial structures

Define homologous structures

• A homologous structure is a structure present in many species that may look or function very differently, but is derived from a common ancestor

• Evidence of DIVERGENT EVOLUTION - common ancestor

Define analogous structures

• They are structures present in two or more species that fulfil the same function but do not originate from a common ancestor

• CONVERGENT EVOLUTION - distantly related species have independently evolved similar traits due to similar selection pressures

Define vestigial structures

• Vestigial structures in an organism that have lost their original function, but once did serve a purpose for its ancestors

• They are evidence of divergent evolution

What is molecular homology, and why do we study it?

• DNA sequences, and amino acid sequences, in a species change over time, due to an accumulation of mutations

• For this reason, it is expected that if two species diverged a long time ago, they would have more differences in their DNA that two species that diverged more recently.

What are the main amino acid sequences studied?

• Hemoglobin

• Cytochrome C

• More similarities = more recent common ancestor = more closely related, this also applies to similarities in DNA sequences when comparing them at corresponding gene regions

Why is determining the relatedness using mitochondrial DNA better?

• Mitochondria contain their own genome

• The mutation rate in mtDNA is much higher than in nuclear DNA, this means that for very closely related species, the mutation rate still ensures that there are enough differences in DNA sequences for use to compare.

• There is no recombination in mtDNA because it’s only inherited from the mother, this means that mtDNA remains unchanged from generation to generation, making it easier to trace back to past ancestors.

What are phylogenetic trees?

They show the evolutionary relationship between organism structures

What are the key structures of a phylogenetic tree?

Root - a line at the origin, representing the earliest ancestor

Branch - each line of the tree

Node - point where branch splits, divergence between taxa

Leaf - end of branch, where present-day species is

State the order of taxa (King Phillip Came Over For Good Soup)

1. Kingdom

2. Phylum

3. Class

4. Order

5. Family

6. Genus

7. Species

What are hominoids, and their distinguishing factors

The superfamily hominoidea - apes

• Increased cranium size

• Shorter spine

• Molar teeth

• Longer arms

• Lack of tail

• Broader rib cage

What are hominins, and their distinguishing factors

The taxonomic point at which humans seperated from other species

• Key characteristic: bipedalism - distinguishes use from chimps/gorillas

• Canine teeth (ours are smaller)

• Brow ridge (ours is smaller)

• Spine curve (we has an S shaped spine, gorilla’s is C shaped)

• Increased cognitive abilities

What characteristics define mammals?

• Hair/fur

• Variety of teeth

• Mammary glands

• Single/lower jaw

What characteristics define primates?

• Flexible spines + hip rotation

• Prehensile hands/feet

• Opposable thumb/big toe

• Sensitive touch receptors

What are the general patterns of hominin evolution?

1. Moving from an arboreal (living in trees) lifestyle to complete bipedalism

2. Shortening of arms and lengthening of legs

3. Faces becoming flatter

4. Skulls becoming rounder

What changes occur in the brain size?

• The brain size is estimated from the volume of an extinct hominin’s cranium

• Improved diet of the hominin leads to increased brain size. With the creation of fire allowing meat to be eaten, meats contain a large amount of fats that provide increased brain development and more energy for this growth

• Specifically the cerebrum of hominin brains become more folded, increasing the TSA so more neurons and enhanced cognitive ability

What are the positives of increased brain size?

• Cognitive benefits lead to improved social outcomes

• Lower predation vulnerability

• Group care + shared mothering

• Cooking + stable food production

What are the negatives of increased brain size?

• The morphological changes = higher energy cost

• higher energy needs

• higher complexity of childbirth

• larger diet

How did a larger brain size impact culture development?

Written and verbal language skills allowed their culture to be passed on via cultural evolution

Other changes produced in hominin evolution

• A more centralised foramen magnum

• Lessening of the brow ridge

• A decreasing arm to leg ratio

What changes in limb structure occured?

• Shorter arms due to less contact with the ground, and allowing the carrying of children, preparing food

• Longer legs makes walking more efficient

• Shorter, more bowl-shaped pelvis provides upright walking support