Genes Evolution & Development L2

Question 1

Mention evidence which helps to prove evolution.

Answer 1

1. Biogeography
2. Natural Selection in action
3. Molecular Genetics

Question 2

What is biogeography?

Answer 2

Distribution of species across env due to env factors

Question 3

Give an example of evidence illustrating biogeography.

Answer 3

1. • Oceanic Islands:
      Native species with specific adaptations to env. Eg. plants, birds, arthropods.
      Similar native species to those on nearest main-land.
      Land mammals, reptiles, amphibians & freshwater fish absent.
2. • Marsupials:
      Marsupials evolved both in Australia & Americas
      No native placental animals in Australia
     Why are native placental animals present in America but not Australia?
      Placental mammals only began to evolve after Australia separated from main land-mass.
      Predicted there must also be fossils of marsupials in Antarctica

Question 4

What is convergent evolution?

Answer 4

Where distantly related organisms independently evolve similar traits due to adapting to similar environments.

Question 5

Examples of convergent evolution.

Answer 5

Eg. Placentals -> Marsupials

1. Anteater -> Banded Anteater
2. Flying squirrel -> Sugar glider
3. Mole -> Marsupial mole
4. North American Porcupine -> Crested porcupine

Eg. Succulents (Desert Plants):
	Fleshy stems -> water storage
	Small surface area of leaves -> reduce water loss
	Spines -> deter herbivores
	Cacti – South America 
	Euphorbs – Old world

Question 6

Give examples of natural selection in action which suggest evolution by natural selection.

Answer 6

• Eg. Pepppered moths:
   Pale spotted form replaced by dark melanic form during industrial revolution.
   Higher bird predation rates on less camoflagued forms in polluted/non-polluted forests during exp. -> significant difference between the no.s of each form of moth depending on env. -> natural selection by evol.
• Eg. Lizards & Hurricane Irma
   Lizards studied & measured on Carribbean islands
   Hurricane Irma
   Measured population again – few weeks later. (No reproduction in interval)
   Average lizard had larger toe pads, longer arms & shorter hind legs
   These adaptations enabled survival in storm?
   Exp. Later proved this as lizards with these traits enabled longer average grip time in wind-force experiments.

Question 7

How can molecular genetics help prove evolution?

Answer 7

Can track evolutionary relationships by comparison of genetic sequences/proteins.

Question 8

What is the molecular clock?

Answer 8

 Proteins from pair of species compared
 Differences in DNA code correlated with incr. distant evolutionary relationship from fossil evidence.
 Genetic differences accumulate at constant rate:
Non-coding sequences of DNA not subject to selectional pressures mutate at a constant rate.

Question 9

What does the molecular clock illustrate/what is it’s significance?
Use examples where appropriate.

Answer 9

 Evolutionary tree of cytochrome c gene correlates with morphological trees.
 Rapid appearance of major bird species/groups after extinction events.
 Helps illustrate relationships – Eg. Falkland wolf -> only native mammal to Falklands. Found to split with fox species on mainland during last glacial maximum due to analysis of genetic sequences.

Question 10

Why is genetic sequence data important?

Answer 10

1. All data sequences agree/congruent with evolution
2. Molecular phylogenetics supports morphological data.
3. Detail sometimes unresolved due to rapid evolution -> more sequences will resolve this.

Question 11

Describe the evolution of olfactory genes in cetaceans.

Answer 11

Evolution of olfactory genes in cetaceans:

• Cetaceans have lost their olfactory receptor genes as return to marine habitat.
• Only use olfactory receptors when breathing/surfacing -> less functional genes for sense of smell required.
• 68% of cetacean genes are pseudogenes (non-coding/functional)
• Non-functioning genes in dog-27%; cow 17%.
• Conclusion: Genes required for olfactory senses not required/selected for by natural selection -> mutations occur in these sequences -> genes become non-functional.

Question 12

Describe the evolution of enamelin.

Answer 12

• Toothless mammals -> non-functioning enamelin gene.

- Time non-functional gene arises correlates to loss of teeth in fossil records.

Question 13

Describe the evolution of lactase persistence in humans.

Answer 13

Lactase persistence in humans

• Highest rates correlate with growth of farming practises. - Highest -> Europe.
• Therefore communities that drink milk more regularly developed higher tolerance.
• Strong evidence of natural selection.
• Individuals with tolerance are selected for.

Question 14

What is the neutral theory?

Answer 14

Neutral theory:
- Many non-coding DNA sequences -> non-functional
 Mutations in these parts of genome not selected.
 Should evolve randomly -> selectively “neutral”.
- Some codon mutations won’t change the amino acid -> multiple seq. can code for same protein.
- Non-coding regions -> best used for molecular clocks