Biology: A 4.1 (SL) Evolution

Evolution

change in heritable characteristics

• characteristics of population are changing over time

  • must be heritable not acquired (traits that are inherited by offspring from parents)

Theory of Evolution

Charles Darwin - by natural selection

Selection Pressures (Darwin)

causes evolution & variation within a population

—> enables organisms that are better adapted to the environment to survive and pass on this advantage to future generations

Selection Pressures (Darwin) - EXAMPLE

Darwin vs. Lamarck Theories

Lamarck - Evolution by Transformation

(ancestral giraffes stretching their neck for food over time)

Darwin - Evolution by Descent w/ Modification (inheritance/selection pressures/adaptation)

Evidence for Evolution

• molecular evidence from DNA, RNA, or amino acid alignment studies

• comparative anatomy & morphology using homologous structures

• evidence from fossil findings

• evidence from selective breeding

Evidence for Evolution - Base DNA/RNA Sequences

evolution occurs

comparing base sequences of same gene in different species —> potential evolutionary relationships

Evidence for Evolution - Base DNA/RNA Sequences (EXAMPLE)

comparing gene sequences which control eye-development (Pax6) in different species

—> conclusion about evolutionary development of vision can be made

Pax Gene - responsible for eye development genes of different animal lineages (evolved from 500+ million years ago)

• as descendant lineages evolved, basic eye-building gene was modified in different ways in different lineages —> rise to diversity in modern animals

Selective Breeding

form of deliberate selection in which humans actively choose which traits should be passed onto offspring

• involves choosing parents w/ particular characteristics to breed and produce offspring —> w/ more desirable characteristics

  • continuous removal of progeny (descendants) - showing less-desired features generation-by- generation —> leads to genetic variation

Selective Breeding - EXAMPLE 1

Selective Breeding - EXAMPLE 2

Tassels & seeds of a wild grass (Teosinte) became male tassels and female ears of modern corn —> selected for

• stalk

• seed size

• nutrient

• oil content

• color

suppression of branching from the stalk resulted in a lower # of ears per plant —> allows each ear to grow larger

Selective Breeding - EXAMPLE 3

modern breeds of domesticated livestock —> differ from animal of origin

• egg-laying hens increased MASSIVELY in size

• dog breeds developed by artificial selection —> Grey Wolves (40,000 years ago)

most breeds related to wild species - can still interbreed

Homologous Structures - Divergent Evolution

similar anatomy but carry out different functions

• developed from COMMON ANCESTOR —> DIVERGENT EVOLUTION

Convergent Evolution

analogous structures that have similar function but different origin

NO COMMON ANCESTOR

Homologous Structures - EXAMPLE

Limbs of Vertebrates - arms, forelegs, wings & fins are similar in anatomy (similar bone structure) —> indicator of having evolved from a common ancestor (divergent evolution)

• may have different functions/purposes - similar design

  • due to different selection pressures (adaptive radiation)

Adaptive Radiation

process of diversifying into a range of different species from a common ancestor

Lava Lizard - on main islands of Galapagos same species can be found

—> 6 smaller islands are closely related but different species found

Analogous Structures

similar form & function

• NOT developed from common ancestor

• different evolutionary origins

—> octopus eye vs. human eye

—> lady bugs vs. birds

Morphology

form & structure of organisms

(less reliable for identifying evidence vs. base sequences)

Speciation 1

species become different after being separated from each other for an extended period of time

• each species is adapting to slightly different conditions

  • Natural Selection - will allow for them to develop in 2 different ways until they become recognizably different

    —> (Finches on Galapagos Islands)

DBQ

Roles of Reproductive Isolation in Speciation

Speciation - formation of a new species of by splitting an existing one

1. Reproductive Isolation -

Abrupt Speciation