Biology Lecture 2 How Populations Evolve

Carolus Linnaeus

a Swedish scientist created a naming system, which is still in use today, as the basis for taxonomy

Taxonomy

the branch of biology concerned with identifying, naming, and classifying species

The Linnaean system includes

a method of naming species and a hierarchical classification of species into broader groups of organisms

In the Linnaean system, each species is given a two-part Latinized name, or

binomial

The first part of a binomial is the

Genus, a group of closely related species

The second part of a binomial is used to distinguish

species within a genus

The two parts of a binomial must be used together to name a

species

The first letter of the genus is

capitalized and the whole binomial is italicized

Naturalists had a hard time with the

interpretation of

fossils:

– imprints or remains of organisms that

lived in the past

Lamarck explained evolution as the

refinement of traits that equip organisms to perform successfully in their environments

He proposed that by using or not using its body parts, an individual may develop certain traits that it passes on to its offspring

Charles Darwin (1809 – 1882)

• was a skilled naturalist who travelled the world observing and documenting the natural world aboard a survey ship called The Beagle over 100 years ago

• coined the phrase “descent with modification” to describe evolution

• also proposed a scientific mechanism for how life

  evolves, a process he called natural selection

Darwin finally published

• The Origin of Species (1859), a book that supported his hypothesis with immaculate logic and hundreds of pages of evidence drawn from observations and experiments in biology, geology, and paleontology

• Scientists regard Darwin’s concept of evolution by means of natural selection as a theory:

Fossils document

differences between past and present organisms and show that many species have become extinct

Paleontologists are

scientists who study fossils

Homology is

• Similarity resulting from common ancestry

• Used as a second type of evidence for evolution

• Related species can have characteristics that have an underlying similarity yet function differently

• signs of descent with modification

ex. arms in different species

Natural Selection example

By spraying crops with poisons to kill insect pests, people have favored the reproductive success of insects with inherent resistance to the poisons

Phenotype

the expressed traits of an organism

genotype

Which is inherited, and many environmental influences

New alleles originate by mutation

a change in the nucleotide sequence of DNA

Allele

One of two or more alternative forms of a gene that arise by mutation and are found at the same place on a chromosome

In multicellular organisms, however, only mutations in cells that produce

gametes can be passed to offspring and affect a

population’s genetic variability

In organisms that reproduce sexually, most of the genetic variation in a population results from the unique combination of alleles that each individual inherits during

Meiosis

A population is

is a group of individuals of the same species that live in the same area and interbreed

We can measure evolution as a change in the prevalence of certain heritable traits in a population over a span of

Generations

Each of the four boxes in the Punnett square corresponds to

a probable “draw” of alleles from the gene pool

Passing through a “bottleneck”

a severe reduction in population size — decreases the overall genetic variability in a population because at least some alleles are likely to be lost from the gene pool

Founder Effect

The type of genetic drift resulting from the establishment of a small, new population whose gene pool differs from that of the parent population – loss of genetic variation

• When a few individuals colonize an isolated island, lake, or other new habitat, the genetic makeup of the colony is only a sample of the gene pool in the larger population

Example of Founder effect

Amish and Mennonite communities in North America were founded by small numbers of European immigrants in the 1700s

Gene flow tends to reduce

differences between populations

Genetic exchange with another population

A population may gain or lose alleles when fertile individuals move into or out of the population or when gametes (such as plant pollen) are transferred between populations

ex. pollen being blown to different towns

“survival of the fittest”

individuals in the context of evolution are those that produce the largest number of viable, fertile offspring and thus pass on the most genes to the next generation

Relative fitness

the contribution an individual makes to the gene pool of the next generation relative to the contributions of other individuals

Three General Outcomes of Natural Selection

Three general outcomes are possible, depending on which phenotypes are favored:

1. directional selection

2. disruptive selection

3. stabilizing selection

Sexual Selection

A form of natural selection in which individuals with certain traits are more likely than other individuals to obtain mates

In some species, males engage in nonlethal combat in the hope of mating with females

Sexual dimorphism:

distinction in appearance based on secondary sexual characteristics, noticeable differences not associated with reproduction or survival