Evolution

Introduction to Microevolution

Microevolution refers to small evolutionary changes that occur within a population over a few generations. These changes can be measured by tracking shifts in the proportion of individuals with certain heritable traits (traits that are passed from parents to offspring).

Genes are the instructions in our DNA that we inherit from our parents, and which determine our traits. Mutations (changes in gene instructions) may alter the traits that we express creating diversity among us and are therefore the source of new alleles. Mutations are quite rare events for most animal & plants species and as such do not play a significant role in microevolutionary changes but may be a factor for species with very short generation times such as bacteria.

The main factors contributing to microevolutionary change are

  • Mutation: A random change in the genetic composition of an organism due to changes in the DNA base sequence

  • Gene flow: The movement of alleles into, or out of, a population as a result of immigration or emigration

  • Genetic drift: The change in the composition of a gene pool as a result of a chance or random event

  • Natural selection: The change in the composition of a gene pool as a result of differentially selective environmental pressures


The Hard-Weinberg Principle

The Hardy-Weinberg Principle is a theoretical concept in population genetics. It states that allele and genotype frequencies in a population will remain constant from generation to generation-that is, the population will be in genetic equilibrium-as long as the below conditions are met:

1. No Selection

2. No Mutation

3. No Migration

4. Large Population

5. Random Mating


  1. No natural selection - if one phenotype has a survival or reproductive advantage, allele frequencies will shift.

  2. No gene flow - immigration or emigration can introduce or remove alleles from the population.

  3. No mutations - mutations create new alleles, altering the gene pool.

  4. Large population size - prevents random changes in allele frequencies (genetic drift).

  5. Random mating - ensures allele combinations occur by chance, not preference.


Gene: a segment of dna with instructions for RNA or protein

Micro evolution : change in allele distribution over time in a population

Allele: an alternate version of a gene

Dominant allele: A expressed in heterozygous individual

Recessive allele- a not expressed in heterozygous

Genotype- to describe what alleles an individual has

Phenotype- trait expressed that we see

Examples: Phenotype roll tongue


Genotype:

AA = homozygous dominant - roll tongue

aa = homozygous recessive - can’t roll tongue

Aa= heterozygous - roll tongue = dominant trait

Gene pool and genetic variation

Gene pool: genes in population

Genetic variation: differences in gene composition


3 sources of genetic variation:


1. Mutations randomly occur

  • rare

  • Must be in eggs/ sperm for sexually reproducing individuals


2. Alterations in genome

* random additions/deletions to the chromosomes


3. Sexual reproduction

  • variation introduced during creation of eggs + sperm

  • mutation- random

  • new allele created

  • Change in allele distribution over time


2 sexual recombination - random

* during egg and sperm creation alleles are exchanged between maternal and paternal chromosomes- make new combinations


3 Genetic drift- A, founder effect - random

* individuals from a population move to a new area and start a new population

* New population is often low in genetic variation

* Increased variation between the populations


3 Genetic drift

Bottleneck effect- random disaster wipes out individuals randomly- change in allele distribution


4. Gene flow- random

* migration of individuals between populations reduce variation between Populations


5. Natural selection

variation introduced during creation heritable traits, one trait has an advantage in that environment and has be better survival and fitness (reproductive success) NOT Random


Mechanisms of nutura selection

  1. Overproduction

  2. limited resources

  3. Genetic variation (eg. color of butterfly)


Adaptive evolution- environment stress dictates which trait is advantageous



6. Artificial selection- Not Random

* humans decide which traits are advantageous and decide who reproduces

Patterns of Natural Selection


* Directional- move towards one extreme

Allele distribution changes to one extreme

B. Disruptive- - move from a range towards both extremes

C. Stabilizing- move from a range towards one mid-point

D. Sexual selection

- intrasexual : members of the same sex fight for the opportunity to mate

-intersexual: females choose males based on various traits

* Often leads to sexual dimorphism- differences in physical traits between males and females


 E. Balancing - maintain full range

Frequency- switch from one trait to the other over time

* environment dictates which trait is advantageous



Quantitative Data

  • Definition: Information expressed as numbers, counts, or measurements.

  • Core Questions: Answers "how much," "how many," or "how often".

  • Examples: Temperature, weight, height, and survey ratings on a 1-to-10 scale.

  • Analysis Method: Evaluated using math and statistical analysis (like averages or percentages).


  • Qualitative Data

  • Definition: Information expressed through descriptions, language, or symbols that capture subjective meaning.

  • Core Questions: Answers "why" or "how".

  • Examples: Interview transcripts, open-ended survey text, photographs, and direct observations.

  • Analysis Method: Evaluated by grouping into themes, categories, or text coding.


Qualitative data describes qualities and characteristics using words or images, while quantitative data measures quantities using numbers and values


Importance of replication:

-check technique

-identify outliers

-account for variation


Biological versus technical Replicates


Biological replicates: # of individuals- 3 mice

  • What they measure: Natural biological variation and diversity within a population.

  • Why they matter: They prove that an experimental effect is real and generalizable beyond a single test subject or sample.



Technical replicates- more than one measure

-test technique

Repeated measurements or assays performed on one single biological sample.

confirm that your lab protocol and equipment are working correctly and giving reproducible readings.


Pseudoreplication is Pseudoreplication is a statistical error that occurs when data points or measurements are treated as independent replicates in an analysis when they are actually related.


Example: measuring ten cells from one animal or five soil samples from one plot


Descriptive statistics help you understand and present raw data. They do not look beyond the immediate data.

  • Central tendency: Mean (average), median (middle value), and mode (most frequent value).

  • Dispersion (spread): Range, variance, and standard deviation.

  • Visual tools: Bar charts, histograms, and pie charts.

  • Example: Calculating the average test score for 30 students in a single classroom


Inferential Statistics

Inferential statistics use probability to test claims and draw conclusions about a wider group based on a smaller representative sample. Because you only look at a subset of the population, these methods always account for sampling error and uncertainty.


Ex: Hypothesis testing: Assessing whether an observed pattern is likely real or due to random chance (t-tests, Chi-Square,