Understanding Standard Deviation in Research

Selection & Evolution

• This chapter covers selection and evolution in three parts: variation, natural selection, and evolution and speciation.

Variation

• Phenotype results from the interaction of genotype and environment.
• Variation can be continuous or discontinuous.
• The environment influences the phenotype.
• Standard deviation (std dev), standard error, error bars, and t-tests, are key tools for statistical analysis.
• Variation refers to the presence of different characteristics within a population.
• Phenotypic variation equals genetic variation plus environmental variation, Vₚ = VG + Vᴇ .

Continuous vs Discontinuous Variation

• Discontinuous variation has a discontinuous distribution, is controlled by one or few genes (monogenic), shows large effects of differing alleles at a single gene locus and has qualitative data.
• Continuous Variation has a normal distribution, is controlled by many genes (polygenic,) shows small effects of alleles at a single gene locus and has quantitative data.
• Discontinuous variation has discrete categories with no intermediates and is little affected by the environment.
• Continuous variation ranges of phenotypes, has many intermediate phenotype between extremes and is affected by environment.
• Examples of discontinuous variation include albinism and sickle cell anaemia.
• Height and mass area examples of continuous variation.

Genetic Variation

• Variation is the presence of different characteristics
• The phenotype results from the genotype and environment interaction.
• Genetic variation mainly comes from meiosis and fertilization, referencing Chapter 16.
• Crossing over occurs at Prophase I.
• Independent assortment occurs at Metaphase I.
• Random fertilization/mating.
• Mutations are a primary source of variations that can produce new alleles.

Environmental Influences on Phenotype

• Environmental factors including nutrients/diet, water availability, light intensity, temperature, chemicals/mutagens, lifestyle and culture can influence phenotypes.
• The environment has a greater effect on polygenes and phenotypes affected by the environment show continuous variation.
• The environment can limit/modify gene expression i.e. influencing size/mass/height.
• The environment can trigger / switch on a gene, for example, low temperature can change animal colour.
• The environment can induce mutation which affects phenotype.
• Dark pigmentation occurs in Himalayan rabbits due to genotype and environment interaction
• At low temperatures, the allele for dark pigment is expressed.
• Dark tips form at ears, paws, nose & tail, which are the coldest parts of the rabbit.
• The gender of the animal is sensitive to temperature/
• A temperature of 32-34°C will cause crocodiles to be male, but below 32°C and over 34°C will cause the crocodiles to be female.
• In Drosophila, at a temperature o f19°C, the fruit fly will have straight wings but at a temperature of 25°C, the fruit fly will have curly wings.
• After a few hours of exposure to UV radiation melanocytes produce melanin in skin, causing skin to tan or form dark spots/freckles, which protects cells from DNA damage.
• Red and blue light are most effective for plant growth.
• Blue light helps with seed germination.
• Red light helps flowers bloom, but leaves will have stretched and elongated appearance.

Statistics in Biology

• The t-test, error bars, and standard deviation are used in Biology
• It is important to know std dev, std error and error bars, alongside t-tests

Maths Skills Required! (P5)

• Formula for the mean: x = Σx/n.
• Other important measures include median, mode, range, and interquartile range.
• You should be able to calculate Standard deviation (s), Standard error (Sᴍ), and the 95% Confidence Interval = ± 2Sᴍ.

Standard Deviation (s) (P5)

• Standard deviation shows the spread of data about the mean (x) in a normally distributed sample and indicates data reliability.
• A small value of s means data is less scattered and more consistent and reliable.
• A large value of s means data is widely spread and results are less reliable.
• Standard deviation can be used to calculate standard error, add error bars to a graph, and calculate t-test value.
• The formula for S = √Σ(X - X)² / (n - 1) where X = each score, X = the mean, n = the number of values, and Σ means we sum across the values.
• The Standard Deviation in Biology is different from what is learned in Maths

Standard Error (Sᴍ) (P5)

• Standard error shows how close a calculated sample mean is to the population's true mean
• It also shows the reliability of the mean and is used to put error bars on graphs.
• A small standard error value indicates that the sample mean value is closer to the actual mean and the mean is more reliable.
• Sᴍ value is between 0 and 1.
• Standard error is calculated using: Sᴍ = s/√n.

Bar Charts with Error Bars (P5)

• Creating bar charts with error bars requires mean (x) value for y coordinates, standard error (Sᴍ,).
• Error bars are lines on bar charts that use the upper and lower limits of a 95% confidence interval, calculated as the mean ± 2 Sᴍ.
• The error bars are a function that test if there is a significant difference between two means.
• If the error bars overlap between two means, then the two means displayed are not significantly different and the null hypothesis is accepted.
• If the error bars do not overlap between two means, then the two means are significantly different and therefore, the null hypothesis is rejected. A t-test must then be performed.

Student's t-test (P5)

• t-tests compare the mean of 2 samples to test if the samples are significantly different
• The t-test should be performed if the data: has continuous/interval data, is normally distributed, the standard deviations are approximately the same and is small as the two samples are under 30 in size.
• Formula to calculate the t value = |X₁ - X₂| / √(S₁²/n₁ + S₂²/n₂).
• After calculating the t value, determine the significance difference.
• Calculate total degrees of freedom: v = (n₁-1) + (n₂-1) = n₁ + n₂ - 2.
• The next step is to check the critical value at p = 0.05.
• Check if critical value in t-test table is lower/higher compared to t-test value calculated
• If the t value calculated is higher than the table value, the two data sets are significantly different, and differences are not due to random error/chance and you must reject the null hypothesis.
• If the t value calculated is lower than value in the table, the means of the data are not significantly different you must accept the null hypothesis, and any differences are due to chance/random error.

Natural Selection

• Part II of the course covers natural selection.
• You will learn about the importance of genetic variation in selection, stabilising, disruptive and directional selection, and examples of evolution by natural selection.
• Also covering antibiotic resistance in bacteria, industrial melanism in peppered moth, sickle cell anaemia The Hardy-Weinberg principle, genetic drift and founder effect and selective breeding / artificial selection

Intro to Natural Selection

• The population is a group of individuals of the same species living in the same area that can interbreed
• Alleles are different forms of a gene
• Allele frequency is the number of occurrences of an allele in a population
• The gene pool encompasses all genes/alleles present in a population.
• The theory of evolution posits that organisms change over time.
• Evolution forms new varieties and species of organisms over time, due to changes in allele frequencies.
• Natural selection mechanism results in evolution
• Charles Darwin and Alfred Russel Wallace proposed the The theory of evolution by natural selection independently in 1858.
• Darwin published ‘On the Origin of Species’ the following year.

The Process of Natural Selection

• Organisms produce many offspring, called Overproduction.
• Organisms have great reproductive potential and reproduce more than is necessary to maintain population and/or can be supported by food supply/ space.
• However, population size is constant over time.
• Individuals/members of the same species compete for survival (intraspecific competition).
• Selection pressure is the environmental factor causing a difference in survival between individuals with different traits
• Variation, a species has variation in phenotype, due to genetic variation, primarily caused by mutations, that introduces new alleles.
• Better adapted organisms pass on advantageous alleles to next generation.
• Over time, frequency of advantageous alleles increases, and disadvantageous alleles are selected against.
• Adaptation is a structure/behaviour/physiological trait that results from natural selection over time, in a species of a population.
• This can lead to speciation, where the forming species has a reproductive barrier from another population

Importance of Variation

• Variation means the presence of different characteristics.
• This leads to different survival rates, reproductive success or failure.
• This allows individuals within a population to adapt to the changing environment and enables a population to survive a changing environment.
• Low genetic diversity = susceptible to disease/environmental changes.

Types of Natural Selection

• When there is selection pressure, natural selection occurs.
• Favourable alleles will always be selected for, less favourable alleles will be selected against.
• This ultimately leads to changes in allele frequency.
• Stabilizing selection occurs when intermediate phenotypes are selected for and extremes of the phenotype are selected against.
• One directional selection occurs, one extreme characteristic is selected for, the other extreme and intermediate phenotypes are selected against.
• With disruptive selection both extreme traits are selected for and Intermediate traits are selected against.

Examples of Natural Selection

• Examples of natural selection include antibiotic resistance in bacteria, industrial melanism in peppered moth, and sickle cell anaemia.
• Antibiotic resistance occurs when antibiotics are no longer effective against bacteria.
• Antibiotic resistance can be spread from bacteria to bacteria
• Many bacteria have penicillinase enzymes can break down penicillin and become resistance to penicillin because the spontaneous/random mutation leads to a change in protein/production of new protein that cannot be targeted by antibiotics
• Antibiotic is the selection pressure. Bacteria with an allele coding for penicillinase has selective advantage and the bacteria survive and reproduce pass down allele to offspring and the resistance frequencies will increase.

Industrial Melanism

• Peppered moth (Biston betularia) spends the day resting on tree barks/branches/trunks and camouflages to protect itself against its predator (birds).
• Before 1849, moths with a speckled appearance was most common, but the number of moths with a melanic/black appearance increased in industrial areas while speckled form still more common.
• Predation by birds is the selection pressure on industrial pepper moths, due to the pollutant changes of the darker shale.
• The allele for black colour increased in frequency in industrial cities

Sickle Cell Anaemia

• The frequency of sickle cell anaemia is highest in areas where malaria is common as SCA and malaria exert selection pressures.
• HSHS: Homozygous for sickle cell alleles, is lethal, so SCA selects against HSHS.
• HNHN: Homozygous for normal Hb allele is susceptible to Malaria and malaria selects against HNΗΝ.
• HNHS: Heterozygous for sickle cell allele have sickle cell trait, but do not die from SCA. They are less likely to suffer severe effects of malaria and contains less Plasmodium in their blood
• This population has selective advantage as They are more likely to survive and reproduce more likely to pass on both HN and HS, therefore as a result The sickle cell allele is maintained within population.

The Hardy-Weinberg Principle

• Used to calculate allele, genotype and phenotype frequencies in populations.
• The 5 requirements of the principle are: The population is large, there is random mating within a population, there is no immigration or emigration, there are no mutations and no selection pressures.
• If frequencies in real life are not as expected, this may mean that one of the assumptions above does not apply
• Equation 1 is for alleles p + q = 1, where the frequency of dominant allele A is p, the frequency of recessive allele a is q.
• Equation 2 is for genotypes p² + 2pq + q² = 1 where Homozygous dominant (AA) is p², Heterozygous (Aa) is 2pq, Homozygous recessive (aa) is q².

Changing Allele Frequency

• Natural Selection can result in allele frequency changes Genetic Drift can result in allele frequency changes caused by Founder effect or Bottleneck effect
• Artificial Selection can result in allele frequency changes

Genetic Drift

• Random process, due to chance
• Changes in allele frequencies fluctuate due to random event
• Can’t be predicted
• More of a affect on small population then large Higher chance of allele will be lost from the population .Unless… There is.
  • migration- founder effect
  • Natural Disaster
  • Bottleneck

Founder Effect

• Is due to migration.
• Few individuals move to a new region
• Isolated become geographically isolated from a larger population
• New population established with a small amount of number of individuals
• Only takes a fraction of Alleles
• May not be Representative Genetic diversity Lower Then-original population Genetic may become genetically distinct from original population. The development with separate species from the original is called Speciation

Bottleneck Effect

• Large decreases the decrease in decline
• Limited due to large Decreasing decreasing in population number
• Common with nature occurring with natural disasters.
• Can be caused due to over hunting the small groups will be more representative due to what had happened Limited for population numbers and what increasing what genetic variety The number but does now increasing genetic diversity

Artificial Selection

• Aka Selective breeding
• Individuals with desired feature are selected to breed
• By humans
• Selection pressure = human.
• Humans choose patents the are most designed and Select offspring with designed feature Repeat for many generations Increase in allele frequency for ideal Characteristics
• Decrease Frequency

Disadvantage of artificial selection.

• Can result in inbreeding
• Leads to an Increase in homozygousity
• Express harmful Recessive alleles
• Loss hybrid in group
• Decrease in genetic variation.
• Offspring may show the desired traits but
• Well adapted in its event. ARTIFICIAL SELECTION
• selection pressure
• Feature for human of selection
• Evolution is not for server
• No high genetics
• Inbreeding can be limited.
• Is the operating
• Faster rate then other process

ARTIFICIAL SELECTION

• To increase increase in milk of derry catted with designed treat
• Increase in resistant for plant crops to get
• Increase synthesis of plant-based synthesis
• Increase maize

Evolution

• This third part of the chapter covers evolution.
• You will learn about Molecular evidence for evolution, Allopatric vs sympatric speeciaton and Extinction

Intro to Evolution

• The theory of evolution describes how organisms change over a period of time.
• A key theory includes how new species have evolved from past pre existence Organism all descendance can from a common ancestor
• The most recently closed to the the specie has a more Common ancestors relationship then previous and There is natural selection that helps them improve through time
• Can be molecular with
• amino acids sequence protein Mitocondrio-dna

Amino Acid Sequence Protein

• The Compered process of amino acid of 2 species . Relationship More closer when it become more similar through species
• And if less acid and close the less time To get from the ancestry is the number one
• Important and the the length and amino sequence.

2) Mitochondrial DNA (mtDNA)

• Used to Compare nucleotide sequence in mtDNA of 2 species
• The less difference in nucleotide sequence, the more closely related the species are.
• Fewer mutations mean less time has elapsed since the most recent common ancestors
• In this process to identify a species that mtDNA doesn’t not undergo crossing over. 2). mutations occur at a constant rate 3 - mtDNA mutates faster than nuclear DNA.and Is Not Associate
• 4. Has a smaller gene to better understand and find quickly

5. The mt DNA passfrom mother to offspring

Species

• Is a Group of similar that features more than with others —Morphological —Physiological —behaviour — biochemical Which inter breed to produce Fettle offspring —ie not reproductive isolate Men can be species and a reproducedly isolate from another Species.

Speciation

• A new formation of species Has with reproductive barriers between population Two species in selection
• In Allopatric Cause by geography isolation

Allopatrie Speciation

• This species that happens to occurs due to geographical barrier.
• The barrier is a river or mountain sea with a difference in what Physically separates
• The difference in breeding becomes population become no gene flow = reproductive isolate
• The more than two population now has different selection and environmental conditions and now more selective to what’s in their area Change has to change allele more frequently with time and has there genetic drifts randomly so This is allopatrite
• Long terms populations have sufficient difference
• Long term populations have a sufficient differences
• The population now will now have to interbreed now and Reproductive isolate and become the new subspecies .

Sympatric Speciation

• All the same location with no physical isolation, where behavior becomes important
• Difference between featured from previous version become not inter breed to each other.
• All cause barriers to the point where can get get get get that one point Then as All the same locations Have different selective points.
• Over time that they continue to evolve in similar groups with different traits.
• The genes drifts as cause population reproductive is.
• This leads to the a new branch off and Are know different that each can.

Sympatric speciation in plans

• Polyploid —has more two set in
• Result in complete and non di junction in meiosis Chromosome Fails to segregate to opposite poles Result in gay with the missing and Non disjunction Chromosomes and fails to segregate to opposite POLE
• cause it can individual to have extra or missing
• down syndrome Triple.
• It has all with. It all comes done to All of them will fails the segregate on POLE. The rest will can trynity Poly Plody has more two chromosomes.

Auto-Polyploid

Combination of Chromosomes from Same Allopolyploid Combination Of Chromosomes from different.

• in generally fusion with two mutated

Will have parents

• cannot interbreed with original species
• new species

What’s a Plody has more then two set