A4.1: Evolution and Speciation

Evolution

A change in heritable traits within a population, occurs via natural selection

Lamarckism

previous evolutionary (false), said evolution occurred via acquired traits during an organism's lifetime

Sequential Evidence

Evolutionary change visible in DNA/RNA/AA, fewer differences=more closely related

Sequence differences accounted by the splitting of ancestral species

Gene Family

Ex. Hox Gene, determines body plan during development, found in organisms w/ clear head-to-tale axis

Selective breeding

Artificial selection, deliberate breeding process to produce desired traits (starts with one species)

Purpose: increase frequency of desired traits in short period of time

Mimics and provides evidence of evolution

Diversity in domesticated animals & Plants (2)

in between breeds and from original wild species

Homologous Structures

Similar anatomical structures w/ different functions, inherited from common ancestors but adapted for different functions

ex. Pentadactyl limbs

Pentadactyl limbs

Similar bone arrangement of five-fingered limb shared in mammals, birds, amphibians, and reptiles

However each limb shows adaptation to their mode of locomotion

Analogous Structures

Different anatomical structures that have similar functions, result of convergent evolution

Inherited from different ancestor, but lived in similar habitats w/ similar selective pressures, thus similar adaptations

Speciation

Creation of new species from pre-existing species

Two separate species begin to evolve independently and can no longer interbreed when brought back together (biological species concept)

Reproductive Isolation

When barriers (not always physical) prevent gene flow between gene pools of two populations

ex. geographic separation (physical barriers)

Divergent/Differential Selection

Different selective pressures cause a population to become different over time

Differences:

-climate

-predation

-competition

Bonobos & Chimpanzees

Separated by Congo river, water level lowered at one point and chimps crossed to Bonobo side

Chimps then subject to same selective pressures as Bonobos and become absorbed into bonobos

Types of Speciation

Allopatric Speciation & Sympatric Speciation

Both require reproductive isolation:

Allopatric Speciation

Geographic barrier that creates physical isolation

Sympatric Speciation (3 types)

The formation of new species in populations that live in the same geographic area

-Behavioral isolation

-Temporal Isolation

-Mechanical isolation

Behavioral Isolation

two populations have different courtship rituals or mating rituals

Temporal Isolation

Two populations breed during different times of the year

Mechanical Isolation

Two populations are anatomically incompatible and cannot transfer sperm

Adaptations

Heritable traits that allow individuals to be better suited to their environments

Adaptive Radiation

Pattern of diversification where species from a common ancestor occupy different, vacant niches (ecological roles) to minimize competition and increase biodiversity

Darwin's Finches

Rapid evolution of single species, results in diversification as individuals with adaptations that match their unique selective pressures survive and reproduce

Seen in beak shape

Finches eventually occupy different niches

Interspecific Hybrids

result of cross-breeding different species, combines useful traits of both (hybrid vigor), but usually sterile

Barriers to hybridization

In evolutionary terms, energy spent on producing sterile offspring is a waste, thus, organisms use techniques like courtship rituals to prevent it

Polyploidy

Organism has more than 2 sets of homologous chromosomes, chromosome duplicate but fail to divide in meiosis

Autotetraploid

(4n), all chromosomes come from same organism, gametes were diploid

When fuse w/ haploid gamete, offspring are triploid (3n) and are sterile

Therefore autotetraploids = different species (biological species concept)

Hybrid

When two species cross breed, contains one set of chromosomes from each parent, chromosomes do not form homologous pairs and hybrid is sterile

Allotetraploid

(4n) - chromosomes are from different species

occurs when chromosomes duplicate but don't divide in meiosis

Can interbreed with other allotetraploids but not parents (therefore different species)

Smartweed

Example of alloploidy, two diploid gametes of two different species mated and formed tetraploid smartweed

Why is polyploidy more common in plants?

Self-pollination - plants possess both male and female parts (therefore don't need to worry about 1 male and 1 female polyploid plant for reproduction)

Asexual reproduction - Infertile polyploids can reproduce asexually

Advantages of Polyploid Crops

Produce seedless (infertile) fruits

Shows hybrid vigor by growing larger, showing better disease resistance