Ecology Lecture | Population Genetics and Natural Selection

Root of genetic drift

natural selection

Why is genetics studied in a population

Genetics is done in a population because its how u get the proportion of the alleles

2 fathers of evolbio

Charles Darwin + Alfred Russel Wallace | note origins of species was published in 1859

What did Thomas Maltuse discover

1. Amount of resources grow at an arithmetic rate whilst the consumption of these resources grow at an exponential rate

When Darwin studied the finches what was the main difference

1. Darwin studied galapagos finches → saw differences in beak shape → which also depended on the availability of the food to them

What is evolution 

1. Gradual genetic change at the population level 

2. Alternatively : the change in frequencies of phenotypes (alleles) in a population

How does gradual change work in terms of passing on traits, and change

1. the change needs to have a genotypic component to be passed on 

2. Note : evolution is all about change / gradual change → not usually one big event 

What are the implications of evolution

1. Evolution does not usually occur in saltations (single bursts) or leaps → punctuated equilibrium → when a large mutation event can shift one species to the other  

2. Evolution acts on heritable characteristics 

   1. Developmental changes may also lead to changes in evolution

   2. As long as there is a small heritable component that can be transmitted 

3. Ontogeny or individual development is not evolution 

Explain evolution using the peppered moth

1. Why was white allele more common?

   1. Fitness : could pass teh gene on to the next via reproduction

   2. Black moths r less common bc they can't reproduce before getting eaten → but white moths can 

   3. But during the industrial revolution, pollution made the trees black which gave advantage to the black moths 

What pushes genetic variation & what is the raw material for evolution

1. Mutations (are what push genetic variation if its a positive mutation) → genetic variation 

Does evolution have a direction

1. Evolution without a particular direction (evolution is not a choice, nor does it have intersectionality, it is dependent on the environment) 

What is another major mechanism aside from natural selection

1. genetic drift (random)

Are phenotypic elements inherited?

No | Phenotypic changes not inherited (unless genotypic component); thus no inheritance of acquired characteristics

What is Natural Selection and what does it lead to

1. Works on the assumption that there is a difference in fitness of different phenotypes → which depend on the environment 

2. Nature working on the presence of survival traits in populations; consistent difference in fitness among phenotypically different organisms 

3. Leads to adaptations → features than exchange fitness 

2 factors that make a trait an “adaptation”

1. Had to be hereditary

2. Has to enhance fitness → has to be better than other phenotypes 

Charles Darwin’s take on natural selection

1. Organisms beget like organisms 

2. Some variations are heritable

3. More offspring than can be supported by the environment are produced each generation

4. Some individuals have higher fitness than others

5. Bottom-line : adaptation 

What are the Mechanisms for variation within populations

1. Genetic factors (alleles)

2. Environmental factors (resources,abiotic factors, etc)

What are Ecotypes

1. population of the same species separate from one another physically which force them to adapt to different environmental conditions → could mate w e/o (likely)

Whats better, higher or lower genetic variation?

1. Note : anything which reduces genetic variation is bad

2. Note : high amount of genetic variation is good, for a population bc it aids in the survival of a species → has a difference in alleles which lets it succeed 

   1. Large populations have high genetic variability

   2. Smaller populations have low genetic variability → bc of inbreeding 

What affects phenotypic variation 

1. Environment vs genetics → nature vs nurture 

2. Hardy Weinberg Equilibrium Mode

What is the Hardy-Weinberg Equilibrium Model

1. (p+q)² = p² + 2pq + q² = 1.0

2. Important bc its a type of null hypothesis meaning if all conditions are met, then evolution is NOT happening in a population 

3. Evolution is the opposing hypothesis

Conditions of the Hardy-Weinberg Equilibrium Model

1. Random mating

2. No mutations

3. Large population size 

4. No immigration 

5. Equal survival and reproductive rates of all genotypes 

   1. No natural selection

What are the Types of natural selection

1. Stabilizing selection → bell curve evolve to average

2. Directional selection → evolve to one side

3. Disruptive selection → favor extreme phenotypes

What could the Significance of Heritability be?

Heritability leads to evolution

What is the Evidence of genetic drift in Chihuahua Spruce

1. Picea chihuahuana now restricted to peaks of Sierra Madre Occidental in N. Mexico

   1. Ledig et al. examined populations to determine if the species has lost genetic diversity as a consequence of reduced population size → due to habitat destruction

      1. Found significantly positive correlation between population size and genetic diversity of study populations 

Population Range and genetic drift

1. > 500 = genetic drift would not occur 

2. < 500 genetic drift would occur

3. <50 = inbreeding

How does Genetic variation in Island Populations work

1. In general, genetic variation is lower in isolated and generally smaller, island populations

   1. Reduced genetic variation indicates a lower potential for a population to evolve / survive

      1. Bc less genetic material → less genes = less ability to evolve 

Characteristic of Bad alleles

1. “Bad alleles” are usually hetero recessive, meaning breeding with a family member could lead to a recessive dominance

What did Saccheri et al.’s experiment on butterflies find?

1. Populations with highest levels of inbreeding had highest probabilities of extinction  

What did Frankham and Ralls find about inbreeding

Frankham and Ralls point out inbreeding may be a contributor to higher extinction rates in small populations

What is Artificial selection

1. is used to describe elective breeding of domesticated organisms to produce or maintain desirable traits 

What is genetic engineering

1. Genetic engineering is the introduction or deletion of genes in domesticated organisms 

   1. These organisms are termed genetically modified organisms or GMO’s

      1. Aka Transgenic Organisms

What are the Unintended Evolutionary Consequences of evolution and agriculture

1. The use of chemicals in agriculture can have evolutionary consequences 

   1. Plant and animal pests may evolve resistance to the chemicals used to control them

   2. Resistance among bests have been shown to be quick and widespread

      1. Vila-Aiub found how Johnson grass quickly evolved resistance to herbicides in Argentina 

what can measure genetic variation

Electrophoresis and PCR are the methods to measure genetic variation

If the population is larger what would be expected from the genetic variation

Generally the larger the population size, the more genetic variation within the population

What influences Phenotypic variation

1. Phenotypic variation may be influenced by genetics (heritability) and/ or the environment → heredity value close to 1 = more variation 

Why is natural selection important?

Natural election is central to how populations adapt to their environment