bio unit 4 aos 2

Gene Pool

all the alleles within a population of a given special

Mutations

changes in sequence of DNA which lead to genetic variation within a population

Silent Mutation

• when a nucleotide is substituted for another nucleotide but does not affect the amino acid coded for

  This is due to the nature of the genetic code where several codons can code for the same amino acid

  The polypeptide chain is not affected

Misssense Mutation

• when a nucleotide is substituted for another nucleotide which changes the amino acid being coded for

Nonsense mutations

• when nucleotide is substituted for another nucleotide

• substituted nucleotide changed the amino acid being coded for to an early stop codon

• renders final protein non functional

Frameshift mutation - insertion

• one or two nucleotides are inserted into the DNA sequence, then all the remaining nucleotides within that gene are pushed forwards downstream

• This changes all the amino acid sequences past the point of the mutation

Frameshift - Deletion

• If one or two nucleotides are deleted from the DNA sequence, then all the remaining nucleotides within that gene are brought back upstream

• This changes all the amino acid sequences past the point of the mutation

Aneuploidy

• chromosomal variation due to a loss or gain of one or more chromosomes

  This results in gametes having either more or less than the usual number of chromosomes for its species

Polyploidy

• one or more complete extra set of chromosomes

Bottleneck effect

• when a catastrophic event or a period of adverse conditions drastically reduces the size of a population (loss of alleles

• The surviving population (often small families) have no choice to inbreed, which can lead to a loss in genetic diversity

Founder’s effect

• the loss of genetic variation that occurs when a new population is established by a very small number of individuals from a larger populatio

• The smaller colonising gene pool is therefore unlikely to reflect the same allele frequency of the original population

• This can lead to increased inbreeding which may result in less genetic diversity

When there is low genetic variation or diversity, this makes the species vulnerable to extinction. So why are they vulnerable?

Because when the selection pressure changes and if no variation exists, all individuals within the population will respond to the change in the same way. This means that many of the individuals within the population may die if the selection pressure is negative.   

Species

a group of organisms that share a genetic lineage and are able to interbreed to create fertile offspring

Prezygotic isolation

• isolation keeps different species from sexually reproducing

• If individuals cannot reproduce, they are considered to be different species and diverge on the tree of life

Speciation

formation of new species in the course of evolution

Allopatric speciation

• occurs when gene flow is interrupted by a geographical barrier which prevent breeding between two populations

• Over time, mutations occur and each environment experiences different selection pressures, driving changes in the allele frequencies of the two separated populations

• Eventually, reaches a point where the two populations can no longer successfully interbreed, becoming two distinct species

Sympatric Speciation

• occurs when two species evolve from an ancestral population while still inhabiting the same geographical area

Selective breeding

• process by which humans manipulate the gene pool of a specific population of species by selecting individuals with desired traits to breed into following generations

• undesired traits breeded out

Advantages of selective breeding

• Higher yield of goods - increase the amount of milk, meat, eggs, or fruits that are produced by the animal or plant

• Healthier products - certain diseases or traits that would normally be harmful or take the lives of many animals and crops can be eradicated

• Survive unsuitable conditions – crops can be tailored to grow on land or soil that they would normally not be able to

• More nutrients provided - plants and animals can be bred to have more nutritional value

• New variations of species - new breeds of species can be developed and can be beneficial to people as well as the animals in the wild

Selective breeding disadvantages

• Reduces allele frequency – the frequency of allele varieties are drastically reduced with selective breeding, making the species less resistant to environmental changes, threatening the survival of the species

• Biodiversity is reduced – selective breeding can replace wild varieties, reducing biodiversity which can put global food security at risk, especially in the face of climate change

• Inbreeding risks – inbreeding with close family members creates higher risk of mutations which can lead to an increase in genetic abnormalities, especially if the conditions are recessive traits

• Time consuming – it takes time to know if a trait has been passed down over many generations, and may require the process to start again if the process has been unsuccessful

Fossilisation

• very rare

• incomplete

• only small sample of population

• doesn’t take into account the varation that exists in a population

• fossils are open to interpretation

• only small amount of remains

Homologous structures

• structures that have been derived from a common ancestor where mutations have occurred that results in structures having different functions

Analogous structures

• structures found in unrelated species that serve similiar purpose due to living in similar environments and exposed to similar selection pressures over a long period of time

Vertigial structures

structures that were inherited from an ancestor but no longer serve a function in species

Divergent evolution

• where there is the build-up of genetic differences between closely related populations within a species, eventually leading to speciation

• It is typically shown when two populations become separated by a geographic barrier and experience different selective pressures that drive adaptations to their new environment

• Over time, the populations become unable to interbreed with one another

Adaptive radiation

• form of divergent evolution in which organisms diversify rapidly from an ancestral species into a wide variety of new species

• This occurs when there is a change in the environment that makes new resources available, creates new selection pressures, and opens the window to new environmental niches.

• This typically occurs when a mass extinction event occurs.

Convergent evolution

• where unrelated species (not closely related) evolve through natural selection independently in similar environments and exposed to similar selection pressures

• As a result, they share analogous structures that have similar functions to survive in their environments, therefore have converged to become alike

Extinction

where there is a permanent loss of a species from the planet

Molecular

Molecular homology is evidence of relatedness between species including DNA and amino acid sequences, mtDNA, and molecular clocks.

What evidence does comparing DNA sequences provide in determining relatedness between species?

• DNA sequences for specific genes can be analysed to compare the difference in nucleotides of the same gene between different species.

• Fewer differences indicate closer relatedness due to more recent common ancestry.

What does gene conservation indicate in molecular homology?

Genes present within species of different groups that are conserved indicate these genes have an important function in the structure or physiological nature of each of the species, such as the genes for haemoglobin and cytochrome c.

How do comparing chromosome banding patterns serve as evidence of molecular homology?

Chromosomes that show similar banding patterns when stained suggest a close relationship and a more recent divergence, observed for example between humans and other great apes.

What information is gained by comparing amino acid sequences in molecular homology?

• Changes in amino acid sequences reflect mutations leading to differences in proteins' functions.

• However, it may not be detected since amino acid sequences might remain unchanged despite DNA differences.

How are molecular clocks used as evidence of molecular homology

use the mutation rate of DNA and proteins to estimate the time when two or more species diverged by counting nucleotide changes over time.

Why is mitochondrial DNA (mtDNA) useful in molecular homology studies?

• abundant

• easier to extract

• mutates faster than nuclear DNA due to fewer repair enzymes, making it useful to compare closely related species.

Why were structural and functional adaptations not always reliable for showing relatedness between species?

Unrelated species living in similar environments can evolve independent structures with similar functions, leading to misleading conclusions if based only on structural and functional adaptation

What types of molecules and techniques can be used to show relatedness between species?

• DNA and amino acid sequences

• mitochondrial DNA (mtDNA)

• molecular clocks

• molecular homology

What types of molecules and techniques can be used to show relatedness between species?

DNA and amino acid sequences, mitochondrial DNA (mtDNA) molecular clocks, and molecular homology.

According to evolutionary theory, how is relatedness between species reflected in their chromosomes, DNA sequences, and proteins?

Species that are more closely related in evolutionary time share more similar chromosomes, DNA sequences and proteins.

How can comparing DNA sequences help determine the relatedness between species?

• If there are few differences between nucleotide sequences of the same gene, species are assumed to be closely related;

• more differences indicate more time since a common ancestor.

What are conserved genes? Give examples of conserved genes

• Genes that are present within different groups of organisms and have been conserved indicate important structural or physiological functions across species.

• The genes for haemoglobin and cytochrome c have been conserved throughout many mammalian species.

Why might comparing amino acid sequences alone not detect all mutations?

Some point mutations are silent, so they don't change amino acids or phenotype and thus are not recognized in amino acid sequence comparisons.

Give an example demonstrating amino acid sequence conservation among species.

All mammals produce the protein casein in milk with structurally similar amino acid sequences and similar function, illustrating a conserved gene.

Why is mtDNA often used to compare closely related species?

mtDNA mutates at a greater rate than nuclear DNA and is relatively easy to extract and sequence, making it suitable for comparisons of closely related species.

How does nuclear DNA compare to mtDNA in terms of usage for species comparison?

• Nuclear DNA is used to compare more distantly related species, while mtDNA is used for closely related species comparisons.

List the shared features of mammals that humans possess.

• Mammary glands that produce milk, give birth to live young (apart from monotremes),

• incisors, canine and molar teeth,

• a neocortex for higher order thinking,

• hair or fur on the surface

• three bones in their ears.

What distinct features separate hominoids from other primates?

• Larger and more complex brains

• molar teeth with five cusps in a 'Y' pattern

• relatively long upper limbs,

• absence of a tail

• shoulder joints capable of 360° rotation.

What advantages does bipedalism provide?

Frees the hands for other uses and provides a raised eye level for better predator detection.

Name skeletal accommodations in humans that facilitate bipedalism.

• Centrally positioned foramen magnum

• S-shaped spine curvature

• carrying angle of femur

• non-opposable big toe with a transverse arch, larger heel

• shallow, bowl-shaped pelvis.

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What does cognitive capacity describe in humans?

• Innate intelligence, ability to learn, plan, evaluate, make decisions, and apply new knowledge and skills, largely due to a relatively big and extensively folded brain.

What features did Australopithecus afarensis possess?

• Short stature (~1.4 m tall)

• flat nose, projecting chin

• small braincase, long arms relative to legs, brow ridge, sagittal crest, large molars, and sexual dimorphism.

Explain what a homologous structure is and why these structures provide evidence of evolution.

• ·  Homologous structures are features that are physically similar in different organisms but have evolved to be different functions during speciation.

• They provide evidence of evolution because they indicate that the species possessing these structures inherited them from a common ancestor because they share similar structures. The structures had different function because during speciation the selection pressure was different

Features required for bipedalism

• centred positioned foramen magnum

• s shaped spine when upright

• angled femur

steps of allopatric speciation

• two or more populations of common ancestor was reproductively isolated by a geographical barrier

• new variations appear in the population due to a mutation

• natural selection favors selected alleles by the different selection pressure

• over a long period of time, new species emerged. If geographical barrier is removed, the species can no longer interbreed and produce fertile offspring

steps of sympatric speciation

• two or more populations of common ancestor was reproductively isolated by a temperal barrier

• new variations will appear in the population due to a mutation

• natural selection favors selected alleles by the different selection pressure

• over a long period of time, new species emerged. If temperal barrier is removed, the species can no longer interbreed and produce fertile offspring

explain why a population with high genetic variation would have an advantage over a population with low genetic variation

The higher the genetic variation, and thus trait variation, within a population, the higher the likelihood that when a natural disaster such as a drought occurs, at least some individuals will have a phenotype that enables them to survive, so the population will survive.

what does an increase in cranal capacity mean?

·  Cranial capacity increased, which implies an increase in brain size and, therefore, intelligence.

·  Increased intelligence would be an advantage to survival as it would allow for strategy in hunting, memory of weather patterns and tool construction and use.

what can be inferred from an anteriorly positioned foramen magnum

·  An anteriorly (towards the back of the skull) positioned foramen magnum implies a shift towards an upright, bipedal posture/stance.

·  A bipedal stance means that the hands are free to carry weapons or tools, and to carry possessions and children, allowing for a nomadic lifestyle and access to a greater range of resources.