Speciation NCEA LEVEL 3

Species

similar organisims that can reproduce in nature to produce fertile offspring

Gene Pool

all alleles in a population

Allele frequency

How often one allele occurs in a gene pool as a proportion of all alleles

Mutation

Random change in DNA sequence - the only source of new alleles

Natural selection

Process by which individuals who are fitter (better suited to the current environment) are more likely to survive, reproduce and pass on their alleles to the next generation

Directional natural selection

Favours phenotype at one end as the best adapted, bell curve shifts one way

Stabilising natural selection

Favours the most common phenotype as the best adapted, selects against extremes

Disruptive natural selection

Favours phenotypes at extremes of distribution, can lead to speciation, selects against the mean

Gene flow

Migration, sharing of alleles between populations

speciation

When populations of one species become so dissimilar over time that they are reproductively isolated, a new species is formed

Allopatric speciation

Formation of a new species which begins with a geographic barrier

Sympatric speciation

Formation of a new species that does not begin with a geographic barrier, usually caused by niche differentiation (a RIM) or polyploidy

Living sympatrically

Living in the same area

geographic barrier

A physical barrier to gene flow eg a river, sea, mountain

Reproductive isolating mechanism (RIM)

A genetic barrier to gene flow

Pre-zygotic RIM

A RIM that means fertilisation does not even occur

Ecological RIM

Where different populations of the same species have preferences that mean they do no come in to contact although they may live in same area

Behavioural RIM

Where appearance or mating behaviours/calls are not recognised as someone to mate with

Temporal RIM

When some aspect of timing is different eg time of being active/awake, breeding season

Mechanical RIM

When physically individuals cannot mate

Gametic RIM

When gametes are incompatible

Post-zygotic RIM

A RIM that means fertilisation does occur but still fertile offspring does not result 

Hybrid inviability

Resulting offspring do not develop or are weak and die early

Hybrid sterility

Resulting offspring survives but is infertile, cannot successfully reproduce

Hybrid breakdown

Resulting offspring survives and can reproduce but next generation is sterile

hybrid

Offspring formed when dissimilar individuals reproduce

polyploidy

Having more than 2 sets of chromosomes ie more than 2n

diploid

Having the usual 2 sets of chromosomes (one maternal and one paternal)

autopolyploid

Polyploid formed from only 1 parent species

non-disjunction

A Mutation where chromatids fail to separate during cell division, either meiosis to produce a diploid gamete, or mitosis to produce a 4n body cell.Usual cause of polyploidy

Divergent evolution

Process by which groups from the same common ancestor evolve and accumulate differences resulting in speciation- We see homologous features as evidence

Adaptive radiation

Divergent evolution where a large number of species are formed in a relatively short space of time, usually due to there being unoccupied niches  

Convergent evolution

Where similar traits arise in unrelated species, usually due to them experiencing similar selection pressures, We see analogous features as evidence

co-evolution

2 unrelated species evolve alongside each other, changing over time due to changes in the other, due to an interspecific relationship they are each others most significant selection pressure

gradualism

Rate of evolutionary change where new species occur at a slow and steady rate

Punctuated equilibrium

Rate of evolutionary change where rapid bursts of speciation are interspersed with long periods of stasis

stasis

Little or no evolutionary change over time

phylogeny

Evolutionary history or development of a group of organism showing descent and relationships between broad groups

Homologous structures (features)

Anatomical features that are derived from a common ancestor but have adapted for different purposes (due to different selection pressures)

Analogous structures (features)

Structural features that serve a common purpose in unrelated species but have different ancestral origins

Vestigial structures

Inherited features that no longer serve a purpose

Interglacial period

Time between ice ages when temperatures are warmer and sea levels are higher

Gondwana

Ancient supercontinent which broke up about 180mya to form most land masses in the southern hemisphere

fossil

Physical evidence of the presence of a once living thing eg bone, teeth, impression in rock

Transitional fossil

Fossil that shows traits of ancestry origin as well as newly derived traits eg a fossil part bird part dinosaur

DNA evidence/genetic relatedness

The more similar any 2 organisms DNA the more closely related they are, the more recently they shared a common ancestor

Nuclear DNA

DNA found in the nucleus, lots of genes, recombines due to meiosis and sexual reproduction

Mitochondrial DNA

DNA found in mitochondria, a few genes, passed down only by females so determines maternal lineage

Y chromosome DNA

DNA that only male mammals have so can be used to determine paternal lineage

Molecular clock

Assuming a constant steady rate of mutation, we can determine how long since 2 groups shared a common ancestor, thus determining relatedness

biogeography

Study of distribution of species through geographic space and geological time