Evolution and Speciation (Chapter 17)

Question 1

What is speciation?

Answer 1

The process by which a new species is produced

Question 2

What is a species

Answer 2

A group of organisms with similar morphological, physiological, biochemical and behavioural features, which can interbreed to produce fertile offspring and are reproductively isolated from other species

Question 3

What is a morphological feature?

Answer 3

A structural feature

Question 4

What is a physiological feature?

Answer 4

How the body works

Question 5

What do biochemical features include?

Answer 5

1) the sequence of bases in DNA molecules

2) the sequence of amino acids in proteins

Question 6

What feature really feature decides whether or not two organisms are the same species?

Answer 6

Whether or not they can interbreed successfully

Question 7

What must happen for a group of interbreeding organisms (organisms of same species) to produce another group of organisms that cannot interbreed successfully with the first group?

Answer 7

The two groups must undergo reproductive isolation

Question 8

What are the two mechanisms of reproductive isolation?

Answer 8

Prezygotic and postzygotic

Question 9

When do prezygotic isolating mechanisms occur?

Answer 9

Before the zygote is formed

Question 10

What are the 4 prezygotic isolating mechanisms?

Answer 10

1) individuals not recognising one another as potential mates or not responding to mating behaviour
2) animals being physically unable to mate
3) incompatibility of pollen and stigma in plants
4) inability of male gamete to fuse with female gamete
5) geographical isolation

Question 11

Which isolating mechanism is more wasteful of energy and resources?

Answer 11

Postzygotic

Question 12

What are the 3 postzygotic isolating mechanisms?

Answer 12

1) failure of cell division in the zygote
2) non-viable offspring (offspring that soon die)
3) viable, but sterile offspring

Question 13

What is almost all the evidence for speciation?

Answer 13

Circumstantial

Question 14

How can you find evidence for speciation?

Answer 14

Can look at populations of organisms at one moment in time (now) and use the patterns to suggest what might have happened or is still happening over long periods of time

Question 15

What is allopatric speciation?

Answer 15

Speciation which happens when two populations are separated from each other geographically

Question 16

What does allopatric speciation require?

Answer 16

Geographical isolation e.g. islands (Hawaiian/Galapagos)

Question 17

How does allopatric speciation by geographical isolation occur?

Answer 17

1) geographical isolation requires a barrier of some sort to arise between two populations of the same species, preventing them from mixing e.g. a stretch of water
2) ∴ the group of organisms on the island interbreed, and because the selection pressure are different from those on the mainland, different alleles are selected for
3) over time, the morphological, physiological and behavioural features of the island population become so different form the mainland population due to mutation and genetic drift that the two populations can no longer interbreed (i.e. reproductive isolating mechanisms may have developed)
4) ∴ a new species has evolved

Question 18

What are two other examples of physical barriers?

Answer 18

• Large areas of forest being cut down, leaving ‘islands’ of forest in a ‘sea’ of agricultural land
• Small-scale barriers for very small or immobile organisms

Question 19

What is sympatric speciation?

Answer 19

When a new species arises without the original populations being separated by a geographical barrier but who biological factors e.g. chromosomal changes and non-random mating, reduce the gene flow

Question 20

How does sympatric speciation occur?

Answer 20

1) Through polyploidy (main way)
2) habitat isolation
3) seasonal isolation (breeding seasons are different)
4) temporal isolation

Question 21

What is a polyploid organism?

Answer 21

An organism with more than two complete sets of chromosomes in its cells - when they spontaneously arise, they are instantly reproductively isolated from their parent population

Question 22

How can a tetraploid organism form?

Answer 22

1) meiosis goes wrong when gametes are being formed, so that a gamete ends up with two sets of chromosomes instead of one set
2) if two such gametes fuse, then the zygote gets 4 complete sets of chromosomes and is tetraploid

Question 23

Describe the characteristics of tetraploid organisms

Answer 23

1) they are often sterile bc there are 4 of each kind of chromosomes and ∴ all 4 try to ‘pair’ up during meiosis 1 and get muddled - ∴ it is very difficult for the cell to divide by meiosis and produce new cells
2) the cell could be able to grow perfectly well and reproduce asexually because mitosis can happen normally, as chromosomes do not need to pair up and behave quite independently

Question 24

Why does polyploidy happen in plants but rarely in animals?

Answer 24

Because most animals do not reproduce asexually

Question 25

How could a tetraploid reproduce?

Answer 25

1) sometimes it can produce diploid gametes
2) if one of these fuse with a gamete from a normal, diploid plant, the zygote will be triploid
3) ∴ a new species has arisen in just one generation as the original diploid plant and the tetraploid cannot interbreed successfully (as the triploid is sterile)

Question 26

Why is a triploid definitely sterile?

Answer 26

Because it cannot produce gametes as it cannot share the 3 sets of chromosomes out evenly between daughter cells (but can grow normally by mitosis)

Question 27

What is an autopolyploid?

Answer 27

A polyploid containing x number of sets of chromosomes all from the same species e.g. tetraploid

Question 28

What is an allopolyploid?

Answer 28

A polyploid containing e.g. 2 sets of chromosomes from one species and 2 sets from another closely related species

Question 29

Why does meiosis happen more easily in an allotetraploid than in an autotetraploid?

Answer 29

1) the chromosomes from each species are not quite identical
2) ∴ the two chromosomes from one species pair up with each other and the two chromosomes from the other species pair up
3) this produces a much less muddled situation than in an autotetraploid, where the chromosomes try and get together in fours ∴ it is much more likely that meiosis will be successful
4) ∴ the allotetraploid is fertile and could produce many gametes

Question 30

Why is the allotetraploid a new species?

Answer 30

Because it cannot interbreed with individuals from its parent species for the same reason as the autopolyploid

Question 31

Give an example of allotetraploidy in spartina

Answer 31

1) S. maritima and S. alterniflora interbred, producing new species S. towsendii (diploid)
2) S. townsendii is sterile bc the two sets of parent chromosomes cannot pair up, so it cannot undergo meiosis successfully and cannot interbreed with either of the parent species - but it can reproduce asexually
3) faulty cell division in S. townsendii produced an allotetraploid plant (S. anglica)) with two sets of chromosomes from S. maritima and two sets of chromosomes from S. alterniflora
4) it is fertile bc the chromosomes can pair up (2 + 2) in meiosis

Question 32

What can be used to reveal similarities between related species?

Answer 32

Molecular evidence from comparisons of the amino acid sequences of proteins and of the nucleotide sequences of mitochondrial DNA

Question 33

What happens in mutations in many proteins?

Answer 33

1) small changes in the amino acid sequence leave the overall structure and function of the protein unaltered
2) typically, the part of the molecule essential for its function (e.g. active site) remains the same, but other parts of the molecule may show changes

Question 34

What does the number of differences in the amino acid sequence between different species give?

Answer 34

It gives a measure of how closely related the species are - the more differences, the less closely related the species

Question 35

What is cytochrome c?

Answer 35

A component of the ETC in OP in mitochondria

Question 36

Why is cytochrome c used to compare species?

Answer 36

A protein with such an important function is expected to have a similar sequence of amino acids in different species because a poorly adapted cytochrome c molecule would result in death of the organism

Question 37

What were the results from comparing the cytochrome c sequence in mice, rats and humans?

Answer 37

Results 1) all 3 molecules consisted of 104 amino acids

2) sequences of mouse and rat cytochromes c are identical
3) 9 amino acids in human cytochrome c are different from the mouse/rat sequence and most of these substitutions in human cytochrome c are of amino acids with the same type of R group

Question 38

What was the conclusion from comparing the cytochrome c sequence in mice, rats and humans?

Answer 38

Mice and rats are closely related with a recent common ancestor and humans are more distantly related with a less recent common ancestor

Question 39

How can differences in the nucleotide sequences of mitochondrial DNA (mtDNA) be used?

Answer 39

They can be used to study the origin and spread of our own species

Question 40

How is human mtDNA inherited and what does this mean?

Answer 40

It is inherited through the female line ∴ a zygote contains the mitochondria of the ovum but not of the sperm

Question 41

Why can changes in the nucleotide sequence of mtDNA only arise by mutation?

Answer 41

Because the mtDNA is circular and cannot undergo any form of crossing over

Question 42

How does mtDNA compare nuclear DNA?

Answer 42

• mtDNA mutates faster than nuclear DNA
• Unlike nuclear DNA, mtDNA is not protected by histone proteins
• OP in the mitochondria can produce forms of oxygen that act as mutagens

Question 43

What do different human populations show?

Answer 43

Differences in mtDNA sequences

Question 44

What evidence has differences in mtDNA sequences provided?

Answer 44

1) evidence for the origin of H. sapiens in Africa and for the subsequent migrations of H. sapiens around the world
2) led to suggestions that all modern humans are descendants from one woman (Mitochondrial Eve) who lived in Africa between 150,000 and 200,000 years ago - this date is derived from the ‘molecular clock’ hypothesis

Question 45

What is the molecular clock hypothesis?

Answer 45

This assumes 1) a constant rate of mutation over time

2) that the greater the number of differences in the sequence of nucleotides, the longer ago those individuals shared a common ancestor
3) the ‘clock’ can be calibrated by comparing nucleotide sequences of species whose date of speciation can be estimated from fossil evidence

Question 46

Give an example of how analysis of mtDNA has been used?

Answer 46

Analysis of mtDNA of 4 species of anole lizard in the Caribbean and adjacent mainland shows that allopatric speciation occurred, originating from one species, A. porcatus

Question 47

How can species become extinct?

Answer 47

1) as a result of natural pressures e.g. climate change or competition from a better adapted species
2) from human activity e.g. habitat loss or poaching

Question 48

What does the IUCN publish annually?

Answer 48

A Red List of threatened species - these species are all under threat of extinction, disappearing forever from the Earth

Question 49

What does the IUCN stand for?

Answer 49

The International Union for Conservation of Nature

Question 50

What has happened due to mass extinction?

Answer 50

• Millions of species have become extinct in the past, sometimes hug numbers at one time in mass extinctions
• However, these events were all natural and some are through to have been caused by sudden chances in the environment e.g. a large asteroid colliding with the Earth

Question 51

Why are we currently facing the likelihood of another mass extinction caused by humans?

Answer 51

• Main reason = habitat loss - man species are adapted for survival in a particular habitat with a particular range of environmental conditions
• Humans are destroying habitats by draining wetlands, cutting down rainforests and polluting the air, water and soil
• Species could also become extinct if we kill too many of them e.g. for sport or food

Question 52

Describe the IUCN red list?

Answer 52

• It has a very high proportion of vertebrates and green plants with a high profile e.g. pandas as opposed to invertebrates and protoctists
• There are no prokaryotes on the list

Question 53

Give an example of how, despite the high profiles of some mammalians species, extinctions continue (tiger)

Answer 53

In India and China, the pressure on the reaming tight populations (roughly 5000 individuals) is intense especially in China where poaching is still common and highly organised as tiger products are thought to cure many ills

Question 54

What has happened to rhinos?

Answer 54

• In 2011, the western black rhino of Africa was declared extinct
• In 2010, the last Javan rhino in Vietnam was killed by poachers, leaving only the small and declining population on Java

Question 55

What are the rhino extinctions a result of, despite years of conservation effort?

Answer 55

1) a lack of political support for conservation
2) an increasing demand for rhino horn
3) internationally organised criminal groups targeting rhinos

Question 56

What do some conservationists think should be done to prevent extinction?

Answer 56

• That it is time to stop concentrating on some of the world’s high-profile species and to turn to others where conservation efforts are likely to have a greater degree of success
• This would involve focusing efforts on certain animals and plants that can be saved at the expense of those that are too difficult or too costly to preserve in the wild
• Conservation programmes now often try to conserve whole ecosystems, rather than concentrating on a single species