10.3 Speciation

Question 1

Define speciation

Answer 1

SPECIATION: an evolutionary process which results in new species evolving from pre-existing species

(reproductive isolation is created)

Question 2

Mechanisms of speciation

Answer 2

1. Allopatric: due to geographical separation
2. Sympatric: reproductive isolation

Question 3

Explain allopatric speciation

Answer 3

Due to geographical barrier - physically isolates populations - evolve separately - cumulative mutation, genetic drift, natural selection - can no longer interbreed - distinct species (speciation)

Question 4

Explain sympatric speciation

Answer 4

In same geographical location but reproductive isolation (genetic abnormalities - different species - interbread between abnormal - speciation)

Chromosomal error: polyploidy - viable but infertile or viable and fertile with other polyploids of the same mutation

Question 5

Define gene pool

Answer 5

GENE POOL: sum of all alleles in all genes in a sexually reproducing population

Question 6

Define evolution

Answer 6

EVOLUTION: cumulative change in the heritable characteristics of a population in successive generations

Changes in allele frequencies in gene pools

Question 7

Mechanisms of evolution

Answer 7

Changes in allele frequencies in gene pools due to:

• mutations: random change
• gene flow: immigration/emigration - movement of alleles
• sexual reproduction: ne geen combinations, change allele frequencies
• genetic drift: change in composition of a gene pool - chance or random event (ex kill have of population)
• natural selection: differentially selective environmental pressures

Question 8

Define genetic drift

Answer 8

GENETIC DRIFT: chnage of a composition of a gene pool due to chance or random event

Faster and more impactful in small populations

Larger population - more stable allele frequencies

Question 9

Explain population bottlenecks

Answer 9

Botlenecks occur when a population experiences a reduction by more than 50%

Causes:

• natural disatsers (fires, floods)
• human induced (overhunting)

Remaining population smaller - more prone to genetic drift - new gene pool will be created

Question 10

Explain founder effect

Answer 10

The founder effect occurs when a small population breaks apart from a larger population colonising new land - more genetic dirft (more diverse the small group) - as it grows no longer representation of original population

Different from bottleneck - the original population remains

Question 11

Types of selection

Answer 11

• stabilising: intermediate is favourable, environmental conditions are stable (ex human birth weights)
• directional: one phenotypic extreme is favourable, gradual change in environmental conditions, stabilising selection after directional completed (ex antibiotic resistance)
• disruptive: both phenotypic extremes are favourable but not intermediate, fluctuating environmental conditions, eventually split into two sub-populations (ex black and white months in different carbon emission areas)

Question 12

Define natural selection

Answer 12

NATURAL SELECTION: change in the composition of a gene pool in response to differentially effective environmental pressure

Question 13

Define reproductive isolation

Answer 13

REPRODUCTIVE ISOLATION: when barriers prevent two populations from interbreeding - separate gene pools

Categories:

• prezygotic: before fertilisation - no offspring
• postzygotic: after fertilisation - non viable/fertile offspring

Question 14

Types of prezygotic and post-zygotic reproductive isolation

Answer 14

Question 15

Microevolution vs macroevolution

Answer 15

Microevolution - within a species

Macroevolution - across species barrier

Question 16

Phyletic gradualism vs punctuated equilibrium

Answer 16

Phyletic gradualism: continuous linage ina acharacteristic

Graduated equilibrium: stable for long time - rapid change

Question 17

Explain phyletic gradualism

Answer 17

PHYLETIC GRADUALISM

speciation smooth and continuous process

Supported by fossil records of horse

Question 18

Explain punctuated equilibrium

Answer 18

PUNCTUATED EQUILIBRIUM

speciation is aperiodic process - sudden chnages after stable periods

Lack of transition fossils