1. Topics 5.4 & Option D 5.4 EVOLUTION (pgs 85-89)

2. What is evolution???
Evolution is the cumulative change in the heritable characteristics of a population.
NOTE: Evolution does not occur within an individual. It occurs within a population or a species.

3. Evolution of the presence of the hoof in horses
Evolution of the modern species of Dog!!

4. Horse Example:
Mutations occurred resulting in genetic variation within the horse population.
These mutations resulted in fewer toes.
Fewer toes=more torque=faster speed
Faster horses could out run predators better, which allowed these horses to survive better and reproduce more until the hoof became the prevalent foot structure.

5. For evolution to take place…
There must be a source of genetic variation between individuals of one species.
Source can be: mutations, crossing over, independent assortment
A change in the frequency of the genes in the gene pool of a population
Caused by natural selection

6. DNA fails to copy accurately
Mutation:
A RANDOM change in the DNA of an organism (deletion, insertion, translocation and inversion)
DNA fails to copy accurately
Most of the mutations that we think matter to evolution are "naturally-occurring." For example, when a cell divides, it makes a copy of its DNA — and sometimes the copy is not quite perfect. That small difference from the original DNA sequence is a mutation.
External influences can create mutations
Mutations can also be caused by exposure to specific chemicals or radiation.

7. Variation as a result of Mutations
Mistakes in the genetic sequence of DNA can lead sometimes lead to a new/different protein being created that results in a different phenotypic result.
Mutations that are harmful, likely will not increase the “fitness” of an individual and will disappear from the gene pool.
Mutations that are beneficial will increase the “fitness of an individual and will remain in the gene pool

8. Fitness: the ability survive and pass on one’s genes to the next generation.
Gene Pool: all the genes present in a given population.
Selective advantage- when nature selects for a particular trait allowing those individuals to have better survival and reproductive success

9. Different mutations…
Neutral mutation: a mutation that does not result in any selective advantage
Ex. When the longer neck of the giraffe provide no benefit, when foliage is plentiful
Harmful mutation: any mutation that decreases the reproductive success of the individual and are therefore selected against. Harmful mutations don’t usually accumulate over time
Ex. When the longer neck decreases survival because it slows down the individuals ability to get away from the overpopulated lion predators in the area
Beneficial mutation: any mutation that increase the reproductive and are therefore selected for. Accumulate over time
Ex. The longer neck increases survival in times of foliage shortage.
Whether a mutation is beneficial or harmful depends on the perspective we look at it from (EX. Antibiotic resistance in bacteria is beneficial for the bacteria, but not for humans)

10. Variation
All the members of a species display variation (differences in their genetic sequences)
Variation is promoted by sexual reproduction
In sexual reproduction 2 different gametes fuse together to produce a zygote.

11. Variation The zygote is genetically different from the gamete donors
The gamete donors contribute only half of their DNA (only 1 of each homologous pair of chromosomes) to the zygote.

12. Variation in Gametes
The gametes produced by a single individual are different from each other as well.
The Law of Independent Assortment states that during Metaphase I of meiosis, homologous chromosomes align themselves randomly.
When they separate, it is random which of the new cells will get a maternal chromosome and which will get a paternal chromosome

13. Independent Assortment

14. Independent Assortment
This allows for different combinations of chromosomes, producing different gametes.
In fact, since humans have 23 pairs of chromosomes, and individual can form 223= different gametes! (and this doesn’t even take crossing over into account)
This is why you and your sibling are not exactly the same.

15. Crossing Over
During Prophase I of meiosis, during synapsis (when homologous chromosomes pair up), non-sister chromatids can exchange genetic material to form chromosomes with a new sequence of genes.

16. The Galapagos Islands 1000 km off the west coast of South America
Made up of 18 islands, formed from volcanoes that rose up from the ocean floor.
Because they are islands, they are geographically isolated (– its difficult for organisms to migrate from the mainland to the islands and vise versa)
Since they are volcanic islands all existing life had to have migrated there through air or water

17. Galapagos Islands

18. Darwin
At the age of 22, Darwin set sail on the HMS Beagle for a 5 year voyage to survey the coastal waters of South America.

19. Darwin’s Journey
Throughout his journey, Darwin observed, recorded and collected specimens of rock, minerals, plants, and animals.
He gathered thousands of specimens
His most famous observations (that support his theory of evolution) were made on the Galapagos Islands

20. Darwin
On his voyage Darwin collected many pieces of physical evidence and observations that he compiled to come up with his theory of natural selection

21. Observations from Galapagos
Evidence of Evolution
Darwin’s Hypothesis
Observations from Galapagos
Unusual animal behaviour: animals are unusually fearless
i.e.: birds may land on your head, iguanas allow themselves to be picked up, sea lions will sit next to you on the beach
These species lived and evolved in a location without natural predators and so they had lost their instinctive fear

22. In this case, instinctive fear was naturally selected against.
Why? What would be the advantage?
Hypothesis: animals would waste energy by running away needlessly (remember, there weren’t any predators on the island)
Could be costly to “run away” because could result in missing out on food (i.e.: fruits dropping from a tree)

23. Darwin’s Finches
Darwin noted that there were many different variations of the finch.
He also noted that each of the Galapagos islands contained a different assortment of finches
He hypothesized that depending on the food available on the island, different traits became more common as it helped survival- Adaptive Radiation
Adaptive radiation is the relatively rapid evolution of species to fill otherwise uninhabited ecological niches

24. Evolution by Natural Selection
Theory proposed by Charles Darwin
Individuals that are the best adapted to their environment will have the greatest chance of surviving and reproducing, thus passing on their genes.
“Survival of the Fittest”- Coined later by Herbert Spencer
The genes that allow individuals to best survive, will be “naturally selected for” by the environment.

25. Variation + Pressure Change
A beneficial mutation is said to increase that individuals “fitness” or gives them a “selective advantage”.
Of course, fitness is a relative thing. A genotype's fitness depends on the environment in which the organism lives. The fittest genotype during an ice age, for example, is probably not the fittest genotype once the ice age is over.
A selective advantage deals with the term natural selection, or the way in which nature favors the survival and reproduction of one individual over another within a population
“Natural variation exists nature acts upon this variation nature selects for specific traits individuals possessing the desirable live to reproduce these traits become more prevalent in a population

26. Process of Natural Selection
variation - individuals in a population vary from one another
selection - some variants reproduce more than others (as a result of competition, environmental change or other selection processes)
Inheritance - parents pass on their traits to their offspring genetically
time - successful variations accumulate over many generations

27. Ex. Giraffe 1. Some giraffe's are born with longer necks than others
2. A change in climate causes a shortage of food and those giraffe with the longer necks are able to survive longer
3. The longer necked giraffes are able to reproduce more as a result
4. The genes for longer necks become more predominant in the population over time

28. Ex. Humans Humans were able to survive as a result of;
Large brain (intelligence)- allowed us to live in communities, build shelters, use fire, use tools etc.
Opposable thumbs- allowed us to grip objects and manipulate tools.
Bipedal- walking on two legs allowed us to use our hands freely and standing up allows us to see higher/further to see potential threats better.

29. Ex: Hedgehogs
Hedgehogs typically defend themselves against predators by curling into a ball and exposing their spines.
Hedgehogs would consider cars predators, and would have the same response to an approaching car.
Hedgehogs that have developed the instinct to flee from a car rather than curling up into a ball will have a greater chance of surviving, and reproducing and passing on this trait – thus this trait will be naturally selected for

30. Ex: Antibiotic Resistant Bacteria
Antibiotics are used to kill bacteria.
If a bacterium cell developed a mutation that resulted in the cell being resistant to a particular antibiotic, then that cell would live while others might die.
Because that cell lived, there is a greater chance it will reproduce and pass on the gene for antibiotic resistance to the next generation.

32. Ex: Antibiotic Resistant Bacteria
All the bacteria that are descendants from this original bacterium cell will carry the gene.
Soon, the entire population of bacteria will have this gene because the ones that didn’t will have been killed by the antibiotics.

33. Ex: Influenza Virus Mutates very easily
Every year a new vaccine must be made against influenza to fight off the new form

34. Ex: Peppered Moth
A species of moth, Biston betularia is native to Manchester, England

35. Peppered Moth
These moths rested on trees that were covered with off-white lichen.
The peppered moths were able to camouflage with the trees an avoid predation from birds.
The rare black phenotype of Biston betularia would be easily seen against the lichen-covered tress and would be easily caught and eaten by birds – therefore prevented from passing on their genes to the next generation.

36. Peppered Moth

37. Prior to the 1850, white moths had the better survival advantage and were naturally selected for.
Virtually all the moths of this species were peppered.
However, in 1850 and the years that followed, the black form of the moths became predominant
Why?

38. The industrial revolution!
Increase in coal-based industry lead to trees becoming covered with soot.
The formerly white trees were now black
The peppered moths no longer were camouflaged, but the black ones were.
The black moths were naturally selected for

39. Since then, there has been a reduction in coal use and the trees are now soot-free (covered in algae) and so both forms (the peppered moth and the black moth) are common.
This is a balanced polymorphism

40. Evidence for Evolution
Fossil record (radiometric dating)
Selective breeding (artificial selection
Homologous structures
Homologous genes (universal genetic code)
Embryonic homology (embryos of different species look almost identical)

41. Fossil Record Fossils are the mineralized remains of organisms.
Did you know??? For a specimen to be considered a fossil in needs to be at least years old.

42. Fossil Formation
Fossils are formed when the remains of a buried organism are gradually replaced by mineral deposits.
When an organism dies, it usually decomposes (with the help of oxygen)
But if it is buried by sediment, the lack of oxygen can prevent decomposition.

45. To have the necessary conditions for fossilization is rare.
Only organisms that die in low-oxygen locations will fossilize
Aquatic organisms in areas where sediment is continuously deposited
Organisms with hard body parts (clams, snails)

47. Artificial Selection Also known as…
Directed breeding
Selective Breeding
Domestication
Individuals that exhibit a particular trait are chosen as parents of the next generation.

48. How does artificial selection work…
Within every species there is some pre-existing variety.
For example a wild tomato or strawberry provide small fruits, but some larger individuals within that population might be naturally occurring
The bigger fruiting plants would then be repeatedly selected artificially by humans (their seeds were kept) to be allowed to reproduce. Creating larger and larger fruits over time.

49. Artificial Selection
Humans have been domesticating animals and plants for more than years.
(Ex: crops, farm animals, household pets)
Canis lupus, the wolf, was the first animal to be domesticated.

50. Today, these domesticated wolves are dogs (Canis lupus familiaris).
Breeders selected certain characteristics and ensured that those characteristics made it into the next generation.
That’s how different dog breeds are made. If a breeder wanted a dog with a curly coat, he or she would allow curly-coated dogs to breed and not allow them to breed with straight-coated dogs.
In nature, the most well-adapted animals are more likely to survive and reproduce, but in dog breeding, the dogs with the desirable characteristics are allowed to reproduce by the breeders.
Today, these domesticated wolves are dogs (Canis lupus familiaris).

51. Domestication of the sea cabbage

52. The 100 year experiment…
Longest running experiment in artificial selection by the Illinois agricultural experiment station
Began in 1896
Test the effects of artificial selection on the oil content of corn seeds
Group A selected for high oil content and Group B was selected for low oil content.
After 76 years Group A increased from 5% oil to more than 18% and group B decreased to less than 1% oil content
Supports the effects of artificial selection

53. Limitations of artificial Selection
Cannot create traits that don’t already exist in the population
Breeders must work within the genetic variability that already exists in the population in order to alter it
Mutations are the only source of new genetic information
Some desirable mutations may be accompanied by undesirable ones
For example an attempt was made to make strawberries that were tolerant of colder weather, but the hardy gene for strawberries was accompanied by a strange white colour. Thus this venture was discontinued .

54. Implications for natural populations
Appearance and structure of organisms can change drastically through artificial and natural selection
Can reduce genetic variability within a population
This loss of variation could present problems
For example: plants bred for sweeter fruits are favoured by humans but also by insects and therefore crops are more susceptible to infestation by pests
can be more prone to certain genetic illnesses including cancers because the alleles for these diseases are linked to the favoured alleles and therefore also inherited

55. Homologous Structures
Evolution suggests that may different species originated from a common ancestor.
Therefore, species that share a common ancestor may have structures that are similar
Homologous structures are structures that are morphologically similar in different species but have different functions.

56. Homologous Structures:
Ex: the forelimbs of mammals/ pentadactyl limb: mammals that are very different from each other possess forelimbs that are quite similar in bone structure and position

57. HOMOLOGOUS STRUCTURES

59. This suggests that all these species evolved from a common ancestor
Over time the original structures were modified as each species evolved (to better suit the organism to its environment)

60. Other Homologous Features
Almost all mammals have 28 skull bones and 7 neck bones, regardless of the size of their skulls of the length of the neck
Vertebrate embryos

62. Analogous features
Organisms with no close common ancestor have evolved to have structures with similar purposes but very different structures
Structures have evolved independently of each other

63. Vestigial structures
Rudimentary and non-functioning/ marginally functioning structure that is homologous to a structure in closely related species
These structures, useful in closely related organisms have become useless or greatly distorted as the organism evolved
Examples: fish that have eye-sockets but no eyes, a running animal that has toes that never touch the ground, organs that serve no apparent function (appendix), hip bones in whales etc..

64. Some large snakes and whales have vestigial hip bones, that do not support walking, but are homologous to hip bones that support hind limbs of other vertebrates
Human Examples:
The appendix: May have once served as a mechanism of leaves in primates
The tail bone: Served as a support structure for an ancestral tail
Wisdom teeth: presently not used in chewing, but functional in primates who possessed larger mouths.
Goosebumps: circular muscles contract to make hair stand up. In animals with fur this would increase insulation

65. Homologous genes and Pseudogenes…
All base pair combinations code for the same proteins regardless of the species
Genes inherited from a common ancestor have evolved because of mutation over time, to create variability
The more closely related 2 species are the more similar their homologous genes are
A universal genetic code and a more recently shared common ancestor allow for hormones like insulin and cortisone to be used for humans from swine or cattle.

66. Pseudogenes…
Genes that have undergone mutation and no longer serve a useful purpose
Ex. Dolphins are thought to have evolved from land mammals. Land mammals have approximately 1000 functioning olfactory receptor (OR) genes and dolphins have all these genes, but only 200 are functioning
Humans have a mutated gene for vitamin C production, where most closely related species can produce their own vitamin C
The stomach of the platypus has 3 mutated genes for producing chemicals for digestion even though they completely lack chemical digestion