BIO-214 #4 Micro & Macroevolution

genetic drift

1. What are Mendelian Genetics?

2. What are alleles? What are the 2 types of alleles?

3. What is the difference between phenotype & geneotype?

4. What are punnett squares?

• Mendelian Genetics

  • how traits are passed from parent to offspring

  • individuals possess two alleles and a parent passes only one allele to their offspring

• Alleles: variation of a gene that code for different traits

  • (capital & lowercase letters: G & g)

• Types of alleles:

  • Dominant

  • Recessive

• Phenotype: physical trait

• Geneotype: genes that code for phenotype

• Punnett squares: shows possible combinations of alleles from parents to predict the probability of an offspring's genotype. 

1. Who is Johann Gregor Mendel?

2. What model system did he use?

• Father of genetics

• Pea plants

• variation will be passed down in mathematical, predicable ways to their offspring

  • Hand pollinated his garden

  • Controlled Data:

    • Each pea plant had a mesh to make sure he was the only pollinator

    • He selected which plants were crossed

    • Plant height, flower color, color of the pea pods (yellow vs green), & shape (round vs wrinkled)

What are the possible allele combinations?

1. Homozygous dominant

   1. GG

2. Homozygous recessive

   1. gg

3. Heterozygous

   1. Gg

• Will receive one allele from each parent (each parent will donate 1 allele)

What is a punnett square?

Dominant alleles are listed first

• exception: sex-linked genes

1. What is microevolution?

2. What is macroevolution?

3. What is population genetics?

4. What are two measurments of population genetics?

• Microevolution

  • evolution on its smallest scale

    • change in allele frequencies in populations

    • Track the shift in allele frequencies (how often are alleles being expressed throughout time in a population

    • Environmental changes → changes in allele frequencies & gene pool→ see if those changes in allele frequencies are permanent

    • Temporary changes are countered by other changes

• Macroevolution

  • gives rise to new species & higher taxomic (classification) groups with divergent characters

• Population genetics

  • studies how selective forces change a population

• Measurements/parameters on population genetics

  1. Changes in allele frequencies

  2. Changes in gene pool

• What is allele frequency?

• A _____ in allele frequency in a population leads to ______.

• How can the allele frequency change?

• Rate at which a specific allele appears within a population

• Change, evolution

• Enviromental factors change the allele frequency

What is a gene pool?

Sum of all the alelles in a population

What is genetic drift?

• Effect of chance on a population's gene pool

  • Smaller populations are more susceptible to genetic drift

  • large populations are buffered against the effects of genetic drift

What is the founder effect?

An event that initiates an allele frequency change in an isolated part of the population

What are the 3 effects that lead to significant changes in a population’s genome?

1. Natural Selection

2. Random/Genetic Drift

3. Founder Effect

1. What is the Hardy-Weinberg Principle?

2. What are the assumptions of the Hardy-Weinberg Principle?

• States that a population’s allele & genotype frequencies are inherently stable UNLESS there’s an evolutionary force

• Gives a basis of comparison

  • When the frequencies change, compare it to the baseline value

  • Different: population is stressed

• Assumptions

  1. No mutations

     1. Most forms of mutations are neutral

  2. No migration (enter a region)

     1. Make the genes more common

  3. Emigration (exit a region)

     1. Makes genes more rare

  4. No selective pressure for/against a phenotype

  5. Infinite population

     1. As accurate as possible

     2. Large populations can even out changes

  6. Matings are random

     1. Some pollinators may select specific flowers

1. Why do biologists use the Hardy-Weinberg Principle?

2. What are phenotype frequencies?

• Gives a mathematical baseline of a non-evolving population

  • Compare the frequencies of the genotypes and the phenotype distribution from then vs now

  • If the frequencies of alleles or genotypes deviate from the expected value of the equation, then the population is evolving

• Phenotype frequencies: heterozygous & homozygous dominant individuals are lumped together

• genetic variation is shifting

  • What factors are leading to these changes (climate change, new prey/predators, diseases, human disturbances)

What is population variation?

Distribution of phenotypes among individuals

What is a polymorphic population?

Has two or more variations of particular characteristics

What is population genetics?

• Population genetics is the study of genetic variation within populations and how this variation changes over time

• provides the framework for understanding how genetic diversity is maintained, how allele frequencies change, and how evolutionary forces like natural selection, mutation, migration, and genetic drift influence populations

What factors/evolutionary forces influence population genetics?

1. Heritability

2. Inbreeding

3. Natural Selection

4. Genetic Drift

5. Gene Flow

6. Mutations

7. Nonrandom Mating

8. Environmental Variance

9. Cline

What is heritability?

• Fraction of phenotype variation that we can attribute to genetic differences (genetic variances) among individuals in a population

  • higher heritability of a population’s phenotypic variation: more susceptible it is to the evolutionary forces that act on the heritable variation

• some changes are just due to mutations & not all genes are expressed (co-dominant genes)

  • Both genes are expressed at the same time (combination of the dominant & recessive genes)

  • Gray cats, pink flowers

  • Incomplete dominance

    • Genes are expressed at the same time, but not at the same place

    • Tuxedo cats with black and white fur at different places

What is genetic variance?

The diversity of alleles & genotypes within a population

• Ex: zookeepers increase a population’s genetic variance in attempt to perserve as much phenotypic diversity as possible

• reduces inbreeding

1. What is inbreeding?

2. What are the results of inbreeding?

3. What happens if a family of carriers (for a deleterious/harmful gene) begins to interbreed?

• the mating of closely related individuals (same direct family line)

• brings together deleterious (harmful) recessive mutations → cause abnormalities

• Interbreeding causes inbreeding depression

  • produce diseased offspring

  • Inbreeding continues too long

  • rates of successful reproduction and offspring survival decrease

    • Feeble, undeveloped, & sick offsprings

How does natural selection lead to selection pressure?

• Natural selection leads to selection pressure by favoring the survival and reproduction of individuals with traits that are advantageous in a given environment.

• These selection pressures shape the genetic makeup of a population over time, leading to evolutionary change

  • big powerful gorilla mates far more than other males → produces more offspring → the genes for bigger size will increase in frequency → the population will grow larger on average

  • Plants that grow too fast may not be able to support themselves

    • Fall over & break the stem

    • Transport of nutrients can’t keep up with their cell divisions

What are two types of genetic drift?

1. Bottleneck Effect

   • a random effect kills a large portion of the population & wipes out a large portion of the genome

     • Mass extinction events (at least 50% gone)

   • the survivors’s genetic structure becomes the enter population’s genetic structure

     • Recessive genes have a chance to become more common

2. Founder’s Effect

   • genetic structure changes to match of the new population’s founding fathers & mothers

     • Ancestral population is still around

   • Causes: a part of the populations becomes isolated

     1. a portion of the population leaves to start a new population in a new location

     2. a physical barrier divides a population

        1. Islands of the Galapagos & Ecuador

        2. Different predators, dieases, environment factors → genetically distinct

• both effects can be so drastic that they become macroevolutions

• What is gene flow?

• What does gene flow change?

• The flow of alleles (gene structure) in & out of a population due to the migration of individual or gametes

• Examples:

  • plants send their pollen far away via wind or by birds

    • they pollinate other populations of the same species

  • developing male lions leave their pride & seek out a new pride with genetically unrelated lionnesses

• Changes

  1. population’s gene structure (alleles)

  2. introduce new genetic variations to populations in different geological locations & habitats

• natural movement of genes flowing

  • One population to a new one

1. What are mutations?

2. How are mutations determined to be beneficial or harmful?

1. Changes to an organism’s DNA & are an important driver of biodiversity in populations

2. If mutations help an organism survive to sexual maturity & reproduce

1. What is nonrandom mating?

2. Why does nonrandom mating occur?

3. What is one form of mate choice? Define it

1. Individual intensionallly choosing their mates

   1. Plants: animal assistance (pollinators)

2. not all individuals are equally participating in reproduction

   1. Health (grew & matured),

   2. which plants produced more flowers/food rewards for pollinators

   3. markings (flower colors, signs leading to food rewards)

3. Occurs due to mate choice

   • female peahens prefer peacocks with bigger, brighter tails

   • Natural selection picks traits that lead to more mating selections

4. Assortative mating

   1. an individual’s preference to mate with partners who are phenotypically similar to themselves

5. based on traits that prove the health & reproductively that cannot be faked

   • Mimic & mask the beneficial traits in plants

What is Environmental Variance?

• Differences/characteristics between individuals that are not inherited but caused by the environment that the organism lives in

  • Surfers have darker skin due to more sun exposure

• Where most of gene variation comes from

1. What is geographical variation?

2. What is one type of geographical variation?

1. Geographical separation between populations can lead to differences in the phenotypic variation between populations

   • Different populations in different regions have variations

     • Get actively attacked or fauned over

2. Cline

   • a measurable gradient in a single characteristic (or biological trait) of a species across its geographical range

   • warm-blooded species tend to have larger bodies in the cooler climates (the poles) so they can conserve better

   • flowering plants tend to bloom at different times depending on where they are along a mountain slope

     • Larger leaves in rainforests (Don’t get torn by rainfall)

What is adapative evolution?

• When natural selection selects beneficial alleles that allow for environmental adaption → increases their frequency in the population AND selecting against deleterious alleles

• evolution affects populations, not individuals

  • Whole gene pools & gene frequencies

• natural selection affects the whole organism, not individual genes

  • Acts with traits that already exist

    • No sudden super necks for giraffes

  • Does the individual live long enough to reproduce? How long will their offspring survive?

What is evolutionary fitness?

• Evolutionary Fitness

  • evolutionary fitness is about success at surviving and reproducing

    • Survival of offspring

    • Ability to pass your genes to your offspring

  • measures how well an organism passes their genes to future generations

• Evolutionary vs Relative Fitness

  • relative fitness: excerise & strength

    • Physically stronger

    • More social individuals survive

    • relative fitness can change

1. What are 5 types of natural selection?

2. As natural selection influences the allele frequencies, what happens to individuals and phenotypes?

• 5 Types of Natural Selection

  1. Stabilizing selection

  2. Directional selection

  3. Diversifying selection

  4. Frequency-dependent selection

  5. Sexual selection

• Individuals

  • individuals can become either more or less genetically similar

• Phenotypes

  • can become more similar or more disparate

What is stabilizing selection? What happens over time?

• Natural selection favors an average phenotype & selects against extreme variation

• The population’s genetic variance will decrease

What is directional selection? What is happens over time?

• Environmental changes lead to one extreme phenotype being favored over both the other extreme and moderate phenotypes

  • peppered moths during the Industrial Revolution adapted to darker wings

• Results in a shift in the population’s genetic variance towards the new, fit phenotype

What is diversifying selection? What is the result of diversifying selection?

• When two ore more distinct phenotypes are advantageous & are chosen over the intermediate phenotype (less evolutionary fit

• Results in increased genetic variance as the population becomes more diverse

What is frequency-dependent selection?

• Favors phenotypes that are either:

  1. Common (positive frequency-dependent selection)

     • decreases population’s genetic variance

  2. Rare (negative frequency-dependent selection)

     • serves to increase the population’s genetic variance

• Australian finches

  • Beak color, feather color, & his ability to sing

    • Can introduce a new marker/trait → observe how the population reacts to the new organism

  • Bobble hat: species with the bobble hat mated more

What is sexual selection? What is one detrimental outcome of sexual selection?

• members of one sex choose mates of the other sex to mate with, and compete with members of the same sex for access to members of the opposite sex

• selection pressure on males & females to obtain matings

• Determinantal outcome: handicap principle

What is sexual dimorphism

• the systematic difference in form between individuals of different sex in the same species

What are leks?

• A place where animals are courting

What is the handicap principle?

• When sexual selection can be so strong that it selects traits that are actually detrimental to the individual’s survival

• Implies that the best males survive the trait’s risk, and are the most fit

• Peacock tail feathers

  • Grow the tail

  • Survive

  • Both points to useful traits he has (territory and high quality food), smart & strong enough too fight off predators

What is the good genes hypothesis?

• Males develop impressive ornaments tos how off their efficient metabolism (ability to fight disease)

• Signalstheir genetic superiority → passes down to their offspring

• traits reflect the good genes that they have

What are honest signals?

• trait that gives a truthful impression of an individual’s fitness

• gives females a way to to find the fittest mates (pass the best gene to their offspring)

Why aren’t living things perfect?

1. Natural selection can only act on existing variations

2. Evolution is limited by historical constraints

3. Adaptations are often compr omises

   1. Gradual changes

4. Chance, natural selection, and the environment interact