Genetic and Phenotypic Variation Quiz

• Phenotypic variation within a species can be quantified
• Two primary types of variation include continuous and discontinuous variation

Continuous Variation

• Characteristics display a graded effect, not falling into distinct classes
• Examples in humans include height and mass
• Controlled by many genes (polygenes), each with an additive effect
• Environmental factors significantly influence where an organism falls on the continuum
• The product of polygenes and environment
• Data can be plotted on a graph, yielding a bell-shaped curve known as a normal distribution

Discontinuous Variation

• Characteristics fit into a few distinct forms, with little overlap between groups
• Example: ABO blood grouping system with four distinct groups (A, B, AB, O)
• Typically controlled by few or single genes
• Environmental factors have minimal influence
• Representable on bar charts or pie graphs

Genetic differences in variation stem from the genotype of each individual, the genes and alleles present, varying from generation to generation because of:

• Mutations, that when in reproductive tissues may be inherited, being the only source of variation in asexually reproducing organisms
• Crossing over with recombinants during prophase I of meiosis exchanges sections of non-sister chromatids, separating alleles of linked genes
• Random assortment of homologous chromosomes at metaphase I of meiosis results in genetically different daughter cells due to random alignment of homologous pairs
• Random mating between individuals within a species
• Random fusion of gametes at fertilization

Environmental Influences on Variation

• Environmental conditions can influence the expression of a genotype, leading to different phenotypes
• Climatic factors, such as temperature, water availability, and sunlight, contribute to variation
• pH levels and the quantity and type of nutrients available also play a role
• Environment affects genetic variation by influencing the mutation rate or switching genes on and off
• Monozygotic twin studies, using genetically identical organisms, can help study the environmental contribution to variation

Environment and Phenotype

• An organism's phenotype results from the interaction of its genotype and the environment
• Identical genotypes exposed to different environmental influences exhibit considerable variety
• Environmental influences and their gradations are largely responsible for continuous variation within a population

How the environment impacts phenotype:

• Alleles provide a blueprint, but expression depends on the environment
• Example: Siamese cats' recessive allele produces heat-sensitive tyrosinase
• Tyrosinase produces melanin, a dark pigment
• The enzyme functions below 33°C
• Extremities are darker due to lower temperatures
• Small Californian plant shows identical genotypes differ in phenotype (height, number of leaves, overall size and shape), and even survival rate, according to the environment in which they live
• Arctic foxes have alleles for fur pigments
• Pigments are produced in warmer temperatures in summer
• Cold winter temperatures lead to white fur for camouflage
• Human height is influenced by diet, with adequate calcium, phosphate, and nutrition needed

Environmental Effects

• Plants grown in nitrogen deficient soil develop less biomass
• UV radiation can disrupt DNA and cause melanomas
• Expression of polygenes is more influenced by the environment

The t-Test

• Determines if the difference between two continuous data sets is significant
• Applicable if data is continuous, from a normally distributed population, standard deviations are similar, and each sample has fewer than 30 values

Analyzing Data

• Equation for the t-test involves calculating $'t$' and $'v$' (degrees of freedom)
• Normal distribution curves share a basic shape but vary in height and width
• The mean represents the measurement at the curve's maximum height, providing an average value
• Standard deviation measures curve width, indicating the range of values

Calculating Standard Deviation

• Standard deviation formula looks complex but is straightforward to calculate

1. Calculate the mean value
2. Subtract the mean value from each measured value
3. Square all the numbers (to eliminate negatives)
4. Add all the squared numbers together
5. Divide by the original number of measurements less one
6. Take the square root

Significant Figures

• Use a calculator for standard deviation
• You will often get a long figure running to many decimal places
• Reduce calculated figures to a certain number of significant figures

Statistical Significance:

• Determine whether the different readings are significant
• You look up value on a t-table
• Need to know the degrees of freedom
• Compare with a probability

Natural Selection

• Natural selection is the process in which organisms better adapted to their environment survive and reproduce, passing on their genes to succeeding generations
• Evidence: fossils demonstrate organisms change over time

Survival of The Fittest Theory

• In 1865 Charles Darwin and Alfred Wallace independently state this theory
• Organisms produce more offspring than can be sustained by resources
• Populations remain constant in size despite overproduction
• Competition occurs within a species for resources
• Genetic diversity is seen among any species population
• Some individuals possess alleles that make them better adapted (fitter)
• Surviving individuals pass on their genes
• Advantageous genes are passed on
• Individuals with beneficial alleles survive

Speciation Through Adaptive Change

• Examples of how natural selection produces changes within a species include antibiotic resistance in bacteria, and industrial melanism

Antibiotic Resistance In Bacteria

• After antibiotic discovery, bacteria become resistant
• Mutation allows some to produce penicillinase, breaking down penicillin
• Penicillin eliminates susceptible forms, selecting for resistant bacteria
• The plasmids can be transferred from cell to cell, or even species, allowing for the resistance to spread

Industrial Melanism

• Some species have two or more distinct forms or morphs
• This polymorphism is exemplified by the peppered moth in England

Molecular Evidence

• Compares Mitochondrial DNA and protein sequences to determine how closely species are related

Overproduction of Offspring

• Darwin noted species potential for exponential increase but that nature rarely sees this, and thus there are high death rates

How organisms over-produce:

• Bacteria divide through binary fission
• Fungi produce large amounts of spores
• Higher plants use vegetative propagation with bulbs, rhizomes, and runners
• Plants produce a lot of pollen
• Animals produce numbers of sperm

Variation Through Selective Pressure

• Where too many offspring are in the same place, limited resources can facilitate competition among individuals
• Those able to survive and adapt have: better adaptations to flee predators, be better able to obtain light or catch prey or be better able to resist disease
• This is a key ingredient to natural selection

Natural Selection Variation

• Individuals with beneficial mutations will produce offspring with similar traits
• This selection depends on genetic differences
• The influence is summarized by Darwin

Extinction

Extinction is a essential process of evolution Species that adapt in structure, habits and instincts will hold vigour and health Some scientists say that 20% of current species will be extinct within the next 30 years

Reasons for extinctions:

• Climate change leads to redistribution
• Habitat loss happens with human exploitation of natural habitats and exploitation
• Competition among species due to increased human development
• Hunting and fishing

Environmental Factors as Forces of Natural Selection

• Selection pressures involve an organism's suitability for survival
• Environmental factors act and limit a population of species and its environmental resistance

Selection:

• Stabilizing selection preserves characteristics by average individuals
• Directional selection favors individuals that vary by a mean
• Disruptive selection favors the extremes

Directional Selection

• Involves distribution curve for any characteristic
• Shifting selection favors individuals toward the mean. Directional selection causes an extreme variation

Stabilizing Selection

• Minimizes the extremes of phenotype range in a population
• Environmental conditions are constant

Disruptive Selection

• Extreme phenotypes occur at the expense of intermediate phenotype
• Not as common as stabilizing selection
• Two forms of temperature occur, disrupting species

Allelic Frequencies

• Mature individuals are capable of breeding
• Alleles of an individual could combine with other individual's alleles

Populations

• Occupy space at particular time
• Could have the potential to interbreed
• All alleles is known as genes
• Amount of times allele occurs in alleles frequency

Genes and Alleles

• Example, cystic fibrosis from thicker than usual mucus
• Combination is heterozygous
• Each pair of cells, genes and alleles
• Each allele is same cell; one pair when considering the gene Pool
• Pair of cell and cystic fibrosis

If there are 10,000 people:

• The frequency to 1.0 in allele
• Everyone had FF genotype; The frequency for allele (F) 1.0
• Frequency for the Ff: The frequency of allele 0.5
• Not made up of one allele by frequency

Hardy-Weinberg Principle

• Mathematical equation is for allele frequencies
• proportion of dominant and recessive remain the same from generation

Hardy Weinberg conditions:

• no mutations
• isolated population
• no selection
• large population
• random mating

How Selective Breeding Changes Allelic Frequencies

When environmental changes affect the probability of an allele surviving, it alters the number of times it occurs Emphasize-do not affect particular mutant allele occurring due to general and random processes rather than specific alleles

Sickle cell Anemia

• HbA-Normal
• HbS-Sickled
• Results in sickle red blood cells
• Homozygous for hemoglobin S:
• Those will sickle cell are disadvantaged
• Homozygous-A
• Normal healthy lives however likely susceptible to malaria
• Heterozygous w/ Hemoglobin:
• Protection to malaria
• Condition of having more tolerance for malaria

Heterozygous

• Advantage where malaria is superior to HbS
• Heterozygous superior and advantageous

Founder effect is created by population

• small fraction of the alleles
• Carry w/ small alleles of population,
• Founder effect occurs as new volcanic islands rise up

The formation of new species (speciation)

• Through the process of speciation comes forms of organisms
• Species a group of ancestry
• Breed w/ another

Process of speciation

• Fertization between two species by hybridization:
• From modern wheat plants
• Polyploidy topic 17.11
• Isolation reproductive followed by genetic change
• Natural selection
• In population genetic drifting results in phenotypic presence
• Adaptive radiation is caused

Allopatric or Sympatric Isolation

• Allopatric: different countries, two species geographically isolated
• Sympatric: same country, two species living together

Pre and post zygotic isolating mechanisms

• The formation of new species occurs from gene. Requires time for gene pools to be sufficiently long.

• These two different mechanisms ensure that groups are reproductively isolated.

• Two Types:

• Prezygotic/Occur Before Mating

• Postzygotic/Occur after mating

Selective Breeding

• Identifying desired characteristics to parent next generation
• Gene pool restricted and desired traits
• Over generations-desired qualities

Selective Pressure

• By selection pressure, humans and natural selection
• Genetic isolation doesn't operate, high herterozgotes
• Carrying out Selective Breeding involves two methods
• Inbreeding to keep desirable characteristics that have risen-loss of vigour,population weakened
• Outbreeding involves the process of breeding unrelated individuals where there are different traits

Modern Day Cattle Factors

• Volume of Milk produced per day
• Milking period Length
• Protein and fat content
• Shape and type of udder
• Amount and type of feed

Process breeding

• Suitable cow process and prodigy tested for sperm and collection
• Artificially process sperm and insemination

Crop Improvements Through Selective Breeding

• Need improvement for increasing world population
• Fungi and diseases contribute to loss of yields by toxins
• Management of pest and pesticides inbreeding is a better/sustainable way
• Deciding traits that are desirable
• Choosing offspring with great characteristics

Disease resistance is key

• Wheat has many diseases/reduced yields such as fungal ones.
• The higher resistance means a greater production Farmers pick most productive crops:
• Picked varieties of resistance
• Scientists cross wheat and disease resistant to create a more higher yields
• Targeted resistance is when to the pathogen happens often
• Pick traits which create most resistance

Modern crop breeders:

• Detect genomes of plants and genes to help and detect regions
• Modern resistance is used to help determine test varieties genes and resistance
• In rice blast is damaging to varieties and Asian ones
• Follow resistant ones
• Rice genes are scanned and used to help help
• Several genes can also increase help

Variations through natural and artificial means:

• Incorporation of Gibberellin Synthesis mutation, the semi-dwarf allele creates little hormones
• Plant and seed variations can be produced by inbreeding and hybridization. Using cross-fertilization can help determine features from each parents. Combining these features can lead to hybrid vigour, giving better and hardier individuals.

Hybridization helps combine genes from different species

• From one plant produces two traits, and one crosses with another
• Then one creates three parts within parts
• Combining genes for species/hybrinds

Test your knowledge of genetic and phenotypic variation, including the roles of meiosis, environmental factors, and statistical analysis like the t-test. Evaluate your understanding of allele combinations, continuous variation, and statistical significance.