Unit 2 - Organisms and Evolution

State some hazards and risks associated with field work and state their control measures

Hazards in fieldwork include adverse weather conditions, difficult terrain i.e uneven surfaces, problems associated with isolation and contact with harmful organinms. Control measures include appropriate equipment, clothing, footwear and means of communication i.e checking weather condition, describing destinations.

Which is more exposed to hazards, working in a lab or a field?

Working in a field may have a greater range of hazards than working in a laboratory.

What must be taken into consideration when sampling wild animals?

Sampling should be carried out in a manner that minimises impact on the wild species and habitats. Consideration must be given to rare and vulnerable species and habitats that are protected by legislation.

Describe the appropriate methods for sampling wild organisms:

The chosen technique, point count, transect or remote detection must be appropriate to the species being sampled.

What is a point count?

A point count involves an observer recording all individuals seen from a fixed point count location. This can be compared to other point count locations or with data from the same location gathered at other times.

What are quadrats and transects used for?

Quadrats, of suitable size and shape, or transects are used for plants and other sessile or slow-moving organisms.

What are capture techniques used for?

Capture techniques such as traps and nets, are used for mobile species.

What techniques are used to sample elusive species?

Elusive species can be sampled directly using camera traps or an indirect method such as scat sampling.

What is scat sampling?

It is an indirect method whereby animal droppings are collected in particular areas, providing information about species abundance and diet.

Name methods used in identification of living things:

Identification of an organism in a sample can be made using classification guides, biological keys, or analysis of DNA or protein.

How can organisms be classified?

Organisms can be classified by both taxonomy and phylogenetics.

What is taxonomy?

Taxonomy is the identification and naming of organisms and their classification into groups based on shared characteristics.

What is the difference between taxonomy and phylogenetics?

Classic taxonomy classification is based on morphology.

What is phylogenetics? And how is it impacting the classification of organisms?

Phylogenetics is the study of the evolutionary history and relationships among individuals or groups of organisms. Phylogenetics is changing the traditional classification of many organisms.

What does phylogenetics use to investigate evolutionary history and relationships? What is a phylogeny?

Phylogenetics uses heritable traits such as morphology, DNA sequences, and protein structure to make inferences about an organism's evolutionary history and create a phylogeny (or phylogenetic tree) — a diagrammatic hypothesis of its relationships to other organisms. Genetic evidence can reveal relatedness obscured by divergent or convergent evolution.

What does the familiarity of taxonomic groups allow:

Familiarity with taxonomic groupings allows predictions and inferences to be made about the biology of unknown or lesser-known organisms and organisms that are better-known (model) organisms.

Give examples of taxonomic groups:

Nematodes, arthropods and chordates are examples of taxonomic groups.

What are model organisms? Give examples:

Model organisms are those that scientists already know a lot about, are easy studied, and have already been studied for many years. For example, the bacterium E. coli; the flowering plant Arabidopsis thaliana; the nematode C. elegans; the arthropod Drosophila melanogaster (a fruit fly); mice, rats, and zebrafish, which are all chordates.

Why are model organisms important?

They are very important in the advancement of modern biology. Information obtained from them can be applied to other species that are more difficult to study directly.

What do indicator species show?

Presence, absence or abundance of indicator species can give information of environmental qualities, such as presence of a pollutant.

How can ecosystems be monitored?

Susceptible and favoured species can be used to monitor an ecosystem.

What shows a species is either favoured or susceptible to an environment?

Absence or reduced population indicates a species is susceptible to some factor in the environment. Abundance or increased population indicates it is favoured by the conditions.

What is the mark and recapture technique and what is the formula for it?

The mark and recapture technique is used for estimating population size. The formula used is

N = MC/R

What does N, M, C and R stand for in the mark and recapture equation?

N = estimate of total population
M = number captured, marked and released in first sample
C = number captured in second sample
R = number of marked recaptures in second sample

What does the mark and recapture method assume?

This method assumes that all individuals have an equal chance of capture, that there is no immigration or emigration, individuals that are marked and released can mix fully and randomly with the total population, there is no birth and death during the sample time, and sampling methods used each time are identical.

Give five examples of marking methods for animals:

Methods of marking animals include banding, tagging, surgical implantation, painting and hair clipping.

What must be taken into consideration when marking animals?

The method of marking and subsequent observation must have minimal impact on the species being studied, thus does not interfere with the individual's normal behavior or make it more conspicuous to preditors.

Describe the three measurements used to quantify animal behavior?

Some of the measurements used to quantify animal behavior are latency, frequency, and duration. Latency is the time between the stimulus occurring and the response behavior. Frequency is the number of times a behavior occurs within the observation period. Duration is the length of time each behavior occurs during the observation period.

What allows the construction of time budgets?

An ethogram of the behaviours shown by a species in a wild context allows the construction of time budgets.

What are ethograms and what do the allow

An ethogram lists species-specific behaviours to be observed and recorded in the study. Recording the duration of each of the behaviours in the ethogram, together with the total time of observation, allows the proportion of time spent on each behaviour to be calculated in the time budget.

Why is it important to avoid anthropomorphism when analysing behavior?

Anthropomorphism can lead to invalid conclusions.

What is anthropomorphism?

When animals are credited with human emotions and qualities.

What is convergent evolution?

Convergent evolution is the process in which organisms that are not closely related independently evolve similar features. Adaptions may take the form of similar body forms, colours, organs and other adaptions which make up the organism's phenotype.

What is divergent evolution?

Divergent evolution is the process whereby groups from the same common ancestor evolve and accumulate differences, resulting in the formation of new species.

What is evolution?

Evolution is the change over time in the proportion of individuals in a population differing in one or more inherited traits.

Explain what occurs to alleles during evolution:

During evolution, changes in allele frequency occur through the non-random processes of natural selection and sexual selection, and the random process of genetic drift.

What does natural selection act on? And explain what natural selection is and what it results in:

Natural selection acts on genetic variation in populations. It works on alleles that increase survival chances. Natural selection is the non-random process that selects individuals based on their survival chances and thus increases their chances of passing on their beneficial inherited traits.

What are mutations?

Mutation is the original source of new sequences of DNA. These new sequences can be novel alleles. Most mutations are harmful or neutral, but in rare cases, they may be beneficial to the fitness of an individual.

How does variation in traits arise?

Variation in traits arises as a result of mutation.

Why can't all individuals of a population survive? What individuals tend to live the longest in a population?

Populations produce more offspring than the environment can support. Individuals with variations that are better suited to their environment tend to survive longer and produce more offspring, breeding to pass on those alleles that conferred an advantage to the next generation, becoming more frequent in subsequent generations.

What does selection result in?

Selection results in the non-random increase in the frequency of advantageous alleles and the non-random decrease in the frequency of deleterious alleles.

What is sexual selection?

Sexual selection is the non-random process involving the selection of alleles that increase the individual's chances of mating and producing offspring.

Describe the difference between sexual and natural selection:

Selected alleles for sexual selection do not increase survival chances, some decrease the survival chances e.g. peacocks long feathers. However, if the organisms does survive then the characteristic gives it a improved chance of reproducing so the allele is more likely to be passed on and will increase in frequency over subsequent generations.

What is sexual dimorphism? Give examples:

Sexual selection may lead to sexual dimorphism, which is the differences in characteristics between two sexes of the same species - other than differences in the sex organs. Examples are in terms of size and colouration e.g. males tend to be larger, more heavily armored, or have more conspicuous markings, structures, or behavior. Females are generally inconspicuous.

What can be the cause of sexual selection?

Sexual selection can be due to male-male rivalry and female choice.

Describe what male to male rivalry and female choice are:

Male-male rivalry has led to the evolution of weaponry in males as large size or weaponry increases access to females through conflict. Female choice has led to the evolution of ornamentation in males as females assess the fitness of males. They want the best alleles for their offspring e.g. to reproduce and survive.

When does genetic drift occur?

Genetic drift occurs when chance events cause unpredictable fluctuations in allele frequencies from one generation to the next.

What size of population does genetic drift impact the most?

Genetic drift is more important in small populations, as alleles are more likely to be lost from the gene pool. Any chance event will randomly affect a sample of a population but small populations are just small samples.

What are population bottlenecks? Give an example of how this is caused:

Population bottlenecks occur when a population size is reduced for at least one generation. This will cause genetic drift particularly in alleles not being selected for or against at this time as they will be low in frequency. Events like natural disasters (earthquakes, floods, fires) can decimate a population, killing most individuals and leaving behind a small, random assortment of survivors.

What are founder effects?

Founder effects occur through the isolation of a few members of a population from a larger population. The gene pool of the new population is not representative of that in the original gene pool.

Describe the importance of bottleneck and founder effects on genetic drift:

Population bottlenecks and founder effects are extreme examples of genetic drift.

How are gene pools affected by genetic drift?

A gene pool is altered by genetic drift because certain alleles may be underrepresented or over-represented and allele frequencies change. If they are underrepresented then they would be low in frequency so after genetic drift they are more likely to be lost from a gene pool.

Describe the relationship between selection pressures and the rate of evolution:

Where selection pressures are strong, the rate of evolution can be rapid.

What are selection pressures?

Selection pressures are the environmental factors that influence which individuals in a population pass on their alleles. They increase the heritability of beneficial traits and reduce the heritability of harmful traits.

Give examples of selection pressures:

They can be biotic: competition, predation, disease, parasitism; or abiotic: changes in temperature, light, humidity, pH, salinity.

What does the Hardy-Weinberg (HW) principle state?

The Hardy-Weinberg (HW) principle states that, in the absence of evolutionary influences, allele and genotype frequencies in a population will remain constant over the generations.

What are the conditions for maintaining the Hardy-Weinberg (HW) principle?

The conditions for maintaining the HW equilibrium are: no natural selection as differences in survival chances or reproductive success will alter allele frequencies, random mating as if there is inbreeding then random mixing of gametes does not occur so the genotype frequencies will change, no mutation as the production of new alleles and the duplication of or deletion of existing alleles will alter allele frequencies, large population size as smaller populations are more susceptible to the effects of genetic drift altering allele frequencies and no gene flow (through migration, in or out) as the addition or removal of individuals from a population will affect the allele frequency.

What can the HW principle be used for?

The HW principle can be used to calculate allele, genotype and phenotype frequencies in populations. Changes in frequencies suggest evolution is occurring.

What is the equation for the HW principle?

P(squared) + 2pq + q(squared) = 1
p = frequency of dominant allele,
q = frequency of recessive allele p2 = frequency of homozygous dominant genotype,
2pq = frequency of heterozygous genotype q2 = frequency of homozygous recessive genotype

What is fitness?

Fitness is an indication of an individual's ability to be successful at surviving and reproducing. Fitness is the measure of the tendency of some organisms to produce more surviving offspring than competing members of the same species. It refers to the contribution made to the gene pool of the next generation by individual genotypes.

What types of fitness is there?

Fitness can be defined in absolute or relative terms.

What is absolute fitness?

Absolute fitness is the ratio between the frequency of individuals of a particular genotype after selection, to those before selection.

What is the equation for absolute fitness?

frequency of a particular genotype after selection
_______________________________________________________________________________
frequency of a particular genotype before selection

What does it mean about the genotype is the absolute fitness equals one?

If the absolute fitness is 1, then the frequency of that genotype is stable. A value greater than 1 conveys an increase in the genotype and a value less than 1 conveys a decrease.

What is relative fitness?

Relative fitness is the ratio of the number of surviving offspring per individual of a particular genotype to the number of surviving offspring per individual of the most successful genotype.

What is the relative fitness equation?

number of surviving offspring per individual of a particular genotype
_______________________________________________________________________________
number of surviving offspring per individual of the most successful genotype

What is co-evolution?

Co-evolution is the process by which two or more species evolve in response to selection pressures imposed by each other.

In co-evolution, what does it mean for one species when the other has a change in traits?

A change in the traits of one species acts as a selection pressure on the other species.

Where is co-evolution commonly seen?

Co-evolution is frequently seen in pairs of species that interact frequently, closely or have symbiotic interactions.

What is symbiosis?

Symbiosis is the co-evolved intimate relationships between members of two different species.

How do the impacts of symbiotic relationships affect individuals?

The impacts of these relationships can be positive (+), negative (-) or neutral (0) for the individuals involved.

Give three examples of symbiotic interactions:

Mutualism, commensalism, and parasitism are types of symbiotic interactions.

Describe what mutualism, commensalism and parasitism are and their outcomes on individuals:

Mutualism: both organisms in the interaction are interdependent on each other for resources or other services. As both organisms gain from the relationship, the interaction is (+/+).
Commensalism: only one of the organisms benefits, the other doesn't gain or lose (+/0).
Parasitism: the parasite benefits in terms of energy or nutrients and the host is harmed as the result of the loss of these resources (+/-).

What does the Red Queen Hypothesis state?

The Red Queen hypothesis states that, in a co-evolutionary relationship, change in the traits of one species can act as a selection pressure on the other species.

What does the red queen hypothesis mean?

Species in co-evolutionary relationships must adapt to avoid extinction. Both species are constantly evolving in response to changes in the other species. E.g. the queen and Alice were both running and when they stopped they were in the same place, they both have to run to avoid extension.

State the disadvantages of sexual reproduction:

Males unable to produce offspring (which is half the population); only half of each parent's genome passed onto offspring, disrupting successful parental genomes

Explain why, despite the disadvantages, sexual reproduction is so common:

Benefits outweigh the disadvantages due to an increase in genetic variation in the population

How is sexual reproduction better compared to asexual reproduction in terms of variation?

Genetic variation provides the raw material required for adaptation, giving sexually reproducing organisms a better chance of survival under changing selection pressures

Use the Red Queen hypothesis to explain the persistence of sexual reproduction

Co-evolutionary interactions between parasites and hosts may select for sexually reproducing hosts. Hosts better able to resist and tolerate parasitism have a greater fitness. If hosts reproduce sexually, the genetic variability in their offspring reduces the chances that all will be susceptible to infection by parasites. However, parasites with increased virulence, better able to feed, reproduce and find new hosts also have a greater fitness. If parasites reproduce sexually, the genetic variation in their offspring increases the chances of some of the offspring having improved ability to exploit their hosts. The selection pressure created by the evolved resistance of the hosts drives the evolution of the parasites to increase their virulence.

Explain how co-evolutionary interactions between parasites and hosts may select for sexually reproducing hosts rather than asexual reproducing hosts:

Hosts better able to resist and tolerate parasitism have greater fitness and this is due to the genetic variation. Parasites better able to feed, reproduce and find new hosts have greater fitness. If parasites reproduce sexually, the genetic variation in their offspring increases the chances of some of the offspring having improved ability to exploit their hosts.

Give an advantage of sexual reproduction:

If hosts reproduce sexually, the genetic variability in their offspring decreases the chances that all of the individuals will be susceptible to infection by parasites. This means the host will be able to resist and tolerate parasitism, therefore showing a greater fitness.

How is asexual reproduction a successful reproductive strategy?

Asexual reproduction can be a successful reproductive strategy as whole genomes are passed on from parent to offspring

Describe asexual reproduction:

In asexual reproduction, just one parent can produce daughter cells and establish a colony of virtually unlimited size over time.

Give an advantage of asexual reproduction, give an example:

Maintaining the genome of the parent is an advantage particularly in very narrow, stable niches or when re-colonising disturbed habitats. An example of re-colonising disrupted habitats is Buttercup plants use stolons to spread into flower beds with clear soil and gain a competitive advantage by dominating the area before other plants can colonise with seeds.

Give examples of asexual reproduction in eukaryotes:

Vegetative cloning in plants and parthenogenesis in lower plants and animals that lack fertilisation are examples of asexual reproduction in eukaryotes

What is parthenogenesis?

Parthenogenesis is reproduction from a female gamete without fertilisation.

Describe the ratio difference in offspring between asexual and sexual reproduction:

Offspring can be reproduced more often and in larger numbers with asexual reproduction.

Whereabouts is parthenogenesis common?

Parthenogenesis is more common in cooler climates, which are disadvantageous to parasites, or regions of low parasite density or diversity

How do asexual reproducing populations cope with changes in their environment?

Asexually reproducing populations are not able to adapt easily to changes in their environment, but mutations can occur that provide some degree of variation and enable some natural selection and evolution to occur

What is meiosis?

Meiosis is the division of the nucleus that results in the formation of haploid gametes from a diploid gametocyte.

Describe the features of homologous chromosomes:

Homologous chromosomes are chromosomes of the same size, same centromere position and with the same sequence of genes at the same loci (location).

Describe the stages of meiosis:

There are two main stages, meiosis 1 and meiosis 2 each consist of prophase, metaphase, anaphase, telophase.

Describe what occurs in meiosis 1:

Prophase 1: The chromosomes, which have replicated prior to meiosis I (Interphase), each consist of two genetically identical chromatids attached at the centromere. The chromosomes condense and the homologous chromosomes pair up. Chiasmata form at points of contact between the non-sister chromatids of a homologous pair and sections of DNA are exchanged.
Metaphase 1: Spindle fibres attach to the homologous pairs and line them up at the equator of the spindle.
Anaphase 1: The chromosomes of each homologous pair are separated and move towards opposite poles.
Telophase 1: Cytokinesis occurs and two daughter cells form.

What are linked genes and what happens when they're separated by crossing over?

Linked genes are those on the same chromosome. Crossing over can create new recombinants resulting in new combinations of the alleles of these genes.

What is chiasmata and what occurs at it?

Chiasmata is the point of contact between two non-sister chromatids belonging to homologous chromosomes. At a given chiasma, an exchange of genetic material can occur between both chromatids. This crossing over of DNA is random and produces genetically different recombinant chromosomes.

Describe what happens during metaphase 1 in meiosis and what independent assortment is:

The orientation of the pairs of homologous chromosomes at the equator is random. Each pair of homologous chromosomes is positioned independently of the other pairs, irrespective of their maternal and paternal origin. This is known as independent assortment.

Describe what occur in meiosis 2:

Each of the two cells produced in meiosis I undergoes a further division during which the sister chromatids of each chromosome are separated. A total of four haploid cells are produced.

Describe how the ratio of chromosomes to chromatids changes throughout meiosis:

During prophase (interphase has just occured, DNA has replicated) 46 chromosomes and 92 chromatids. At the end of meiosis 1, there are 23 chromosomes and 46 chromatids. At the end of meiosis 2, there are 23 chromosomes and 23 chromatids.

How is the sex of birds mammals and some insects determined?

The sex of birds, mammals and some insects is determined by the presence of sex chromosomes

What determines the development of males in the majority of mammals?

In most mammals the SRY gene on the Y chromosome determines development of male characteristics