Evolution

1
Evolution

• Genetic Variation, Extinction and
  Diversification

2
Overview

• Genetic Variation
• Mendels Laws
• Independent Assortment
• Crossing Over
• Mutations
• Change in Chromosome Number
• The Common Genetic Code

• Extinction and Diversification
• Reason for Mass Extinction
• Diversification
• Five Major Extinctions
• The Sixth Extinction
• Extinction Vs. Religion

• Readings and Questions
• Bibliography

3
Genetic Variation

• The inheritable traits of organisms lead to
  genetic variation.
• The origins of genetic variation directly relate
  to sexual reproduction, and include mutations
  (changes in the base pairs of DNA), segregation
  (random assortment of one of each chromosome pair
  into an egg or sperm cell), and recombination (an
  event during meiosis in which specific DNA is
  shuffled).

http//www.accessexcellence.org/AB/GG/
4
Mendels Laws

• Gregor Mendel is known as the father of modern
  genetics due to his contributions to genetics
  made by studying heredity throughout various
  generations of pea plants.
• His studies led to three laws
• 1 The sex cell of a plant or animal contains
  only one
• allele for different traits, but not both
  factors needed
• to express the traits
• 2 Characteristics are inherited independently
  from
• other characteristics (i.e. trait for hair
  colour isnt
• dependent on trait for eye colour)
• 3. Each inherited characteristic is determined
  by two heredity genes, one from each parent which
  determine whether a gene will be dominant or
  recessive.

www.corbis.com
5
Independent Assortment

• Each somatic cell within a human contains two of
  each type of chromosome.
• When gametes are produced, the chromosomes
• separate so that each gamete only contains one
• allele for each trait.
• Out of the 23 pairs of homologous
• chromosomes, it all comes down to
• random chance as to which one of
• the two chromosomes is inherited
• by the offspring
• Because of random chance, two gametes
• virtually never contain the same DNA
• This explains why everyone (except
• identical twins) is unique because
• they are genetically different

http//anthro.palomar.edu/biobasis/default.htm
http//anthro.palomar.edu/biobasis/default.htm
6
Crossing Over

• Crossing over refers to the breaking during
  meiosis of one maternal and one paternal
  chromosome, the exchange of corresponding
  sections of DNA, and the rejoining of the
• chromosomes.
• The result of crossing over is
• a combinations of alleles not
• present in either parent
• This process is also called
• recombination
• Crossing over leads to greater genetic variation
  amongst populations than that resulting from
  independent assortment alone.

http//anthro.palomar.edu/biobasis/default.htm
7
Mutations

• Mutations are rare, random events which are very
  important for evolution
• The are usually non-beneficial to organisms,
  however they are also usually recessive, meaning
  unless two mutations are coupled together, the
  mutation will not be expressed
• All mutations are alterations in a sequence of
  DNA and can occur from chemicals, radiation, or
  through errors in DNA replication
• Genetic variation depends on mutations within
  germinal cells. (Although mutations often occur
  in somatic cells i.e. cancer only mutation in
  germinal cells have the chance to be inherited)
• Mutations or chromosomal abnormalities also
  occur, where species can end up with too many or
  too few chromosomes.
• This can be fatal or lead to various disorders.

8
Point Mutations

• Point mutations occur due to a mistake in the DNA
  replication, or damage by a chemical mutagen, and
  they include
• 1 results in only one amino acid in the sequence
  being changed.
• Both 2 and 3 are frameshift mutations which can
  result in either many different amino acids being
  altered, or a stop codon being read (early or
  later than usual).

1. Substitution 2. Deletion AAA CCC GGC
AAA AAG CCC GGC AAA AAG ACC GGC AAA AAC CCG GCA
AA 3. Addition/Insertion AAG CCC GGC AAA AAG ACC
CGG CAA A
http//www.accessexcellence.org/AB/GG/
Nelson Biology 12
9
Chromosomal Mutation

• Chromosomal Mutations lead to
• an inactivation of the gene if the
• translocation occurs within the
• coding segment.

http//www.accessexcellence.org/AB/GG/
Translocation Inversion Chromosome 1 5 ATG
GCA 3 Normal 5 AAT GGC TAT 3 Chromosome
2 5 TAGC AAG 3 Chromosome 3 TTA CCG
ATA ? ? Chromosome 1 5 TAGC GCA 3
After 5 AAT GCC TAT 3 Chromosome 2 5 ATC
AAG 3 Inversion 3 TTA CGG ATA
10
Change in Chromosome Number

• Irregular number of chromosomes, as well as
• structural modification in a chromosome
  can
• have drastic effects on an individual
• Polyploidy results when an individual
  inherits
• more than 46 chromosomes due to an improper
• separation in meiosis.
• Aneuploidy results when individuals inherit
• less than 46 chromosomes.
• Down syndrome (trisomy 21) is the most
• common disorder, causing mental retardation,
• and distinctive physical traits

http//www.ndsu.nodak.edu/instruct/mcclean/plsc431
/chromnumber/number2.htm
11
The Common Genetic Code

• Humans are 99.9 identical to chimanzees when
• referring to their DNA.
• In 1987, scientists were amazed when British
• researchers showed that a human gene could
• be inserted into a lowly yeast cell and function
  
• perfectly well.
• The Human Genome Project suggests trends that
  genes performing various functions in lower
  animals have been maintained through evolution
  even in human DNA (though sometimes modified).
• The thread of genetic similarity connects us to
  nearly 10 million other species today, and more
  importantly, back to one common ancestor over 3.5
  billion years ago.
• Most importantly, amongst all living organisms,
  the instructions for reproducing and operating
  are encoded in chemical language, represented by
  A, C, T, and G, the initials of 4 chemicals.

www.corbis.com
12
Extinction and Diversification

• Extinction is the evolutionary termination
• of a species caused by failure to reproduce
• and death of all remaining members of the
• species the natural failure to adapt to
• environmental change.
• Diversification is the opposite it refers to a
  species growth and evolution into a greater
  variety of that species and potentially new
  species
• They occur in cycles a long period of
  diversification eventually halts when an
  extinction occurs, and diversification must start
  over.
• Extinction always occurs, and can be caused by a
  species food requirements, predation, or
  habitat.
• Extinction is the expected fate of a species,
  rather than a rarity.

www.corbis.com
13
Reasons For Mass Extinction

• Crater impact is one of the
• major reasons that is believed
• to cause mass extinction
• 65 million years ago, the
• Chixulub Crater smashed into the earth,
  releasing the equivalent energy of 100 million
  megatons of TNT. At the same time, the dinosaurs,
  along with many other species became extinct.
• As further support, rock samples from 95
• locations worldwide show high levels of
• iridium, a rare metal in the Earths crust,
• abundant in meteorites.
• This event however is the only mass
• extinction to be in certain correlation
• with crater impact.

http//www.aros.net/lambo/ele001/ele001.htm
Terrestrial Impact Structures http//www.aros.net/
lambo/ele001/ele001.htm
14
Abrupt Fall in Sea Level

• Another theory that is believed to lead
• to mass extinction is abrupt falls in sea
• level.
• Each of the three largest extinctions in
• that last 250 million years corresponds
• to a major sea level change.
• This lead to the conclusion that falls in
• sea levels have detrimental effects on the
• diversity of marine invertebrates.

www.corbis.com
15
Giant Eruptions

• Giant eruptions coincide with mass extinctions
  more so than any other factor
• The best known series of eruptions occurred
  throughout 1 million years, between 66.5-64.5
  million years ago, when over one million cubic
  kilometers of basaltic lava was poured out from
  under the Earths surface.
• Having no similar eruptions in our history
• to compare these eruptions with, it is hard to
• imagine the effects they would have on climate.
• The three largest extinctions during the past 250
  
• million years occurred at times of both
  sea-level
• fall and flood-basalt eruption.

www.corbis.com
16
Diversification

• Diversification of new organisms rarely happens
  quickly, as life seldom rebounds from extinction
  over a short time, possibly due to extreme change
  in habitat.
• If we substantially diminish biodiversity on
  Earth, we cant expect the biosphere to just
  bounce back. It doesnt do that. The process of
  diversification is too slow, James Kirchner,
  professor of earth and planetary science, at UC
  Berkeley
• Scientists have developed methods through looking
  at fossils to determine rates at which new
  organisms appear and disappear.
• From these studies, they have determined it takes
  nearly 10 million years to recover from global
  extinction, thus proving evolution doesnt speed
  up in response to rapid bursts of extinction.
• Studies of diversification are fairly recent, and
  it is not yet clear on what all the limiting
  factors of diversification are.

17
The 5 Major Extinctions

• The Ordovician Mass Extinction
• (438 million years ago)
• Vertebrates, along with armored jawless
• fish appeared shell bearing marine
• invertebrates dominated.
• High levels of iridium are not associated
• with this extinction, therefore ruling out
  crater impact.
• This extinction seems to be linked with a major
  climate change
• The extinction occurred in two waves the first
  when an ice age began, and the second when it
  ended.
• Although this is generally accepted as a major
  extinction, some paleontologists feel that as
  more fossils are collected from all regions of
  the world, this may in fact have been a
  relatively minor event.

www.corbis.com
18
The Late Devonian Mass Extinction

• This extinction occurred 360 million
• years ago, when amphibians along with
• trees and forests, insects, and bony fish
• appear land plants radiated.
• During this time period, there was a
• worldwide extinction of coral reefs and
• their related fauna, along with many other
• groups of plants and animals.
• Some iridium anomalies have been detected around
  that time period from China and Western Europe,
  however they are hardly comparable to the levels
  associated with the Chixulub Crator
• At the time there are indications of climatic
  changes, and major changes in sea-level and ocean
  chemistry.
• Notably, carbon isotope shifts indicate a rapid
  period of diversification before the extinction.

www.corbis.com
19
The Permo-Triassic Extinction

• 245 million years ago marked the largest
  extinction of all time.
• Douglas Erwin, a famous paleobiologist, marked it
  as the Mother of Mass Extinctions.
• An estimated 57 of all families, and 97 of all
  marine animals became extinct.
• This was a very rapid extinction, almost
  certainly taking place within 1 million years,
  and probably much faster than that.
• At this time, life on land had evolved enough so
  that a small coal bed was created in Australia,
  however after the extinction, no more coal was
  laid down anywhere for at least 6 million years.
• The levels of iridium from this time period are
  normal
• Most importantly, this extinction coincides with
  the largest volcanic eruption known throughout
  the Earths history.

20
The End-Triassic Mass Extinction

• Occurring 208 million years ago, after reptiles,
  amphibians, and insects all radiated, and
  coniferous trees appeared and modernized.
• In 1999, a team of geologists reported that a
  massive eruption took place around this time
  period which marked the beginning of major plate
  tectonic activity that began splitting the
  Atlantic Ocean
• However, many critics have pointed out that the
  eruption seemed to have occurred after
  Triassic/Jurassic boundary, and hence after the
  extinction.
• The extent of this extinction itself is partly at
  question, as scientists have been unable to
  determine how big it actually was.
• Essentially more research is required to
  determine why this extinction occurred, and to
  what extent it did.

21
The Cretacious/ Tertiary Extinction

• Also known as the extinction of the dinosaurs,
• which marked the beginning of the current age
• of the mammals.
• This extinction occurred 65 million years ago,
• killing off all large reptiles, leaving mammals
• to radiate, and angiosperm plants to dominate.
• The Chixulub Crater smashed into earth around
  this time period, in addition to drops in sea
  level, and large volcanic eruptions.
• In comparison to the Permio-Triassic Extinction,
  this remains relatively small, as only 20 - 25
  of all species were brought to extinction.
• Although famous for the extinction of dinosaurs,
  many other species
• became extinct at this time.

www.corbis.com
22
The Sixth Extinction

• What is the sixth extinction? Its the next
  annihilation of vast numbers of species. It is
  happening now, and we, the human race, are its
  cause, according to Dr. Richard Leakey, the
  worlds most famous paleoanthropologist.
• Each year, between 17 000 and 100 000 species are
  wiped out.
• According to Dr. Richard Leakeys figures, 50 of
  all the Earths species will have become extinct
  over the next 100 years, and humans are using
  almost half of the energy available to sustain
  life on Earth.
• According to a United Nations report, almost 25
  of the worlds mammals face extinction in the
  next 30 years
• Extinction of species is mainly occurring due to
  industrialization combined with rainforest and
  wetland destruction.
• The UN report also noted that factors leading to
  mammals extinction continue with ever
  increasing intensity.

23
Extinction Vs. Religion

• Over two centuries ago, the bones of a fossil
  mammoth were collected in North America.
• At the National Institute of Sciences and Arts in
  1796, anatomist Baron Georges Cuvier argued that
  the bones came from a unique species, which no
  longer lived, and therefore was extinct.
• Cuviers deduction completely contradicted
  religious beliefs of the time, as it was believed
  that a creator would not allow any of his
  creations to disappear from the earth.
• This stirred up numerous debates, culminating 60
  years later, with the writings of Charles Darwin.
  

www.corbis.com
www.corbis.com
24
Summary

• Genetic variation relies on the inheritable
  traits of an organism.
• Mendel, the father of modern genetics gave
  insight to alleles, independent assortment and
  dominant recessive genes.
• Crossing over occurs between paternal and
  maternal chromosomes, creating a chromosome
  different from those of either parent.
• Mutations, crucial for evolution, rarely occur,
  and are caused by erorrs in DNA replication
  including insertion, deletion, translocation, and
  inversion.
• We are related to all living organisms, getting
  down to A, C, T, and G.
• A combination of crater impact, change in sea
  level, and eruption is thought to have caused the
  five major extinctions.
• Of the five extinctions, the Permo-Triassic
  Extinction is by far the largest.
• Both the UN and the worlds most famous
  paleoanthropologist agree that humans are the
  cause of the sixth extinction.

25
Questions

• How do both crossing over and independent
  assortment increase genetic variability? Include
  in your answer an explanation of why two
  individuals will never be genetically the same
  (aside from twins).
• Explain how mass extinctions are most likely the
  cause of multiple effects, rather than a single
  cause.
• What is the Sixth Extinction? Why is it
  occurring, and what is its main cause?
• Readings
• Huge Genetic Variation Found http//www.wired.com
  /news/medtech/02C12862C452142C00.html
•  
• The Sixth Extinction Leakey, Richard, Lewin,
  Roger, http//www.well.com/user/davidu/sixthextinc
  tion.html

26
Bibliography

• Genetic Variation, Diversification and Mass
  Extinction Nelson Biology 12
• Biological Basis of Heredity ONiel, Dennis,
  http//anthro.palomar.edu/biobasis/default.htm
• Independent Assortment of Chromosomes No author,
  
• http//www.biology-online.org/2/2_meiosis.htm
•  
• Biology Glossary No author, http//www.pcsresearc
  h.com/bt/Glossary.cfm?TermE
•  
• Mutations, Mutagen, and DNA Repair Montelone,
  Beth,
• http//www-personal.ksu.edu/bethmont/mutdes.html
  types
•  
• Genetics No author, http//mason.gmu.edu/jlawrey
  /bio1471/genetic.html
•  
• Variation and Mendels Laws, Other Sources of
  Genetic Variation No author,
• http//www.anthro.mankato.msus.edu/biology/evolut
  ion/index.shtml
•  
• Biodiversity Glossary of Terms No author,
• http//www.wri.org/wri/biodiv/gbs-glos.htmlCD

27
Bibliography

• The Sixth Extinction Leakey, Richard, Lewin,
  Roger, http//www.well.com/user/davidu/sixthextinc
  tion.html
•  
• Extinction! MacLeod, Norman, http//www.firstscie
  nce.com/site/articles/macleod.asp
•  
• The Common Genetic Code No author,
  http//www.pbs.org/wgbh/evolution/library/04/4/l_0
  44_02.html
•  
• Quarter of Mammals face extinction Podger,
  Corrine, http//news.bbc.co.uk/1/hi/sci/tech/20003
  25.stm
•  
• Extinction, Cowen, Richard,
• http//www-geology.ucdavis.edu/GEL3/Cowenextinct
  ion.html