Bio Review: Exam 1

What Earth looked like 3.8 Billion years ago?

Early Earth:

Hadean “Hell” Eon: 

-Lasted ~800 million years

-No Oceans

-No free Oxygen

-Planet was fully molten

-No protective atmosphere

-Towards the end of Hadean, Earth cooled in about 150 million years (fast in  geologic time)

-Earth was bombarded by asteroids, which caused cracks on the surface.  Steam &  gas was released and allowed for the formation of an atmosphere -Clouds formed & rain gave rise to oceans

-No ozone layer, little UV protection

-Ends between 4.2 and 3.8 billion years ago with first signs of life Source: http://geologycafe.com/images/timescale_highlights.jpg

what is History of Evolutionary Theory?

If you want to learn more check out uncp sociology

Key Time Points:

Time

Event

4.6 BYA

Earth Forms

4.0 BYA

Earth begins to cool

~3.8 BYA

First Life forms

2.5 BYA

Oxygen accumulates  

(photosynthesis)

1.7 BYA

1st Eukaryotes

1 BYA

1st Multicellular OrganismsIf you want to learn more check out bateral

450 MYA

1st Land Plants

420 MYA

1st Land Animals

250 MYA

Permian Extinction

230 MYA

1st Dinosaurs

200 MYA

1st Mammals

65 MYA

K-T Extinction

2 MYA

First Humans

Panspermia-theory that life first evolved elsewhere in the universe but was seeded  to Earth Don't forget about the age old question of bis 2b midterm 2

What Earth looked like 3.8 BYA

-Molten rock

-All life must have been aquatic

-No free Oxygen

-Created reducing atmosphere

-Electron adding- molecules form very readily

-High Energy Environment

who is Gregor Mendel?

-Little to no UV blocking

4 Steps to Life on Early Earth:

1.) Abiotic Synthesis of Organic Molecules

-Miller-Urey Experiment attempted to recreate Earth’s early atmosphere in  1953

-In early 1990’s we discovered that earth’s early atmosphere was  predominantly composed of CO2 and N2, neither of which were found in  original experiment

-Samplings of the more modern experimental “oceans” that form contain the  building blocks of life (amino acids, nucleotides, sugars, lipids, ATP), and  were formed in only one week

2.) Formation of Polymers

-Polymers (protein, DNA) form when monomers (amino acids, nucleotides)  get together and form a chain

-Role of Clay

-Positively charged, rich in iron and zinc, which attracted negatively charged monomers Don't forget about the age old question of 3 oxopentanal

-Would indicate that first life formed near clay-rich shores

3.) Formation of Protobions

-Aggregates of abiotically produced organic molecules surrounded by a  membrane

-Lipids

-Hydrophobic tails and hydrophilic heads form together to create  liposome (lipid bilayer)

-Forms cavity that can hold chemicals-begins to look like a cell

4.) Origin of Heredity Material

-First hereditary material was likely RNA

-RNA can be formed abiotically more easily than DNA can

-Can replicate itself (even more likely in presence of Zinc)

-Contains hereditary information

-Has catalytic properties-can act as an enzyme (unlike DNA)

-Recent research suggests that RNA can be composed completely of sugars  and hydrogenous bases, both components that would have been found on  early Earth

-Viroids-may have led to first life

-Tiny particles of raw RNA, smaller than a virus  

-Enough genetic information to infect a plant and trick the plant’s genetic  machinery into replicating a viroid

-Because they cannot replicate on their own, viroids still cannot be  considered life

History of Evolutionary Theory We also discuss several other topics like opsm the palms

People to Remember:

-Anaximander -Greek Philosopher-Transmutation, common descent -Carolus Linnaeus -Binomial Classification

-James Hutton -Gradualism-Geologic differences happened over long  periods of time

-Adam Smith -Competition

-Jean-Baptiste Lamarck -Acquired Traits (giraffes) We also discuss several other topics like the number of waves passing the observer per second is

-Thomas Malthus -Population growth limited by resources

-George Cuvier -“Catastrophism”, fossils (extinction occurs) -Charles Lyell -Uniformitarianism-“Present is the key to the past” -Charles Darwin -Species change through time, common descent -Alfred Russel Wallace -Wallace’s Line, natural selection

Darwin: 

Modern Five Parts of Darwin’s Theory:

-Individuals vary

-Populations tend to overbreed relative to available resources, leading to a struggle  fro survival

-Better variations have better survival  

-Survivors will reproduce & non-survivors won’t (not always necessary criteria) -Traits leading to better survival & reproduction must be heritable

Do Individuals vary?

Yes!  

Do populations tend to overbreed?

Yes- Oak trees put out many more seeds that can possibly survive.  Somewhere  between 0.01-0.1% of seedlings are expected to survive

-One oak tree will release over one thousand acorns in its lifetime

Do better variations for a particular environment have higher survival rates? Rosemary and Peter Grant- worked on Daphne Major Island in Galapagos -Two of Darwin’s finches live on this island-large and medium ground finch -Variation in head & beak size in medium ground finches

-Survival of these birds is based on seed availability

-1977-Severe La Nina

-Extreme drought, extreme population decline (from 1,400  

finches to 200 finches in just one year)

-Soft seeds quickly eaten, leaving only hard seeds remaining

-Birds with longer and deeper beaks out-survived those with  

smaller beaks

-1984- El Nino, very wet year

-Abundance of small seeds (can fall out of large beaks)

-Smaller beaked birds survived better than those with large  

beaks

-Solidifies theory that better variations have better survival rates

Do survivors have more offspring and pass on their selected traits to the next  generation?

-Grants plotted beak size of parents by the beak size of offspring & found very  strong correlation – strongly suggests that traits are heritable

-Evolution actually changed the average beak size across generations, causing more  birds to have large beaks

-Concludes that traits leading to better survival and reproduction must be heritable Why isn’t everyone satisfied?

Implications Involved in accepting this theory:

-Earth must be old enough for evolution to have occurred

-Fossils should show evidence of change through time

-Older rock strata should have fewer fossils of modern species than younger rock  strata

-Fossils of intermediate forms must be found

Is Earth Old enough?

-Hutton & Lyell both believed so

-Depth of canyons & thickness of rock strata both indicate very long & gradual  natural process

-We can now date the oldest found rocks to be 4.6 billion years old -Found oldest life to be about 3.8 billion years old

-Earth is old enough

Do fossils show that species are mutable?

-Cuvier showed that extinction occurred and that recent species were no longer  extant

-Darwin’s fossils

-Megatherium-Giant sloths 1.1m tall & weighed up to 6,000 lbs

-Toxodon- capybara like species 1.5m tall & weighted up to 1.5 tons -Glyptodon-Giant armadillos, 1.5m tall, weighed as much as average sedan -Fossils were closely related to animals alive at the time, but were not the same  species

Do younger rocks strata have more modern fossils than older rock strata? -Lyell’s data on mollusks proved this to be true

Are there fossils of intermediate forms?

-3 years before his death, Archaeopteryx fossils were found

-Has traits of both birds and reptiles-intermediate form

-Provides solid evidence of transitional forms

-Whales, Horses & Tiktaalik (intermediate between fish & amphibian) all good  examples of intermediate forms

Gregor Mendel (1822-1884)

Mendel’s Five-Element Model:

-Parents transmit information about traits to their offspring

-Each individual receives two copies of each factor to encode each trait

-Not all factors are the same and different combinations lead to different traits -Two factors do not blend

-Presence of a factor does not guarantee it will be expressed- it can be latent

Genotype

-Alleles found in individuals

-Homozygote dominant has different genotype that heterozygote dominant -AA differs from Aa even if both flowers are purple

Phenotypes

-AA=Aa  

-Physical characteristics of organisms

-Phenotype ration 3:1

Mendel’s 1st Law of Heredity-Principle of Segregation

-Two parental alleles segregate during gamete formation to be rejoined at random  during fertilization

Monohybrid Cross:

-Parental Generation Ry * rY

-3:1 ratio

Dihybrid Crosses-Mendel’s 2nd 

Law of Heredity-Law of  

Independent Assortment

Parental Generation:  RRYY * rryy

-F1- RrYy

- Dihybrid Crosses lead to 9:3:3:1  

phenotype ratio

-In Dihybrid cross, alleles of each  

gene assort independently

Source:  

http://cnx.org/resources/ceb880bf9a58402dc053bb94ff94ec158ffc2a3a/Fig 

ure_12_03_02.png

Mendel was Unaware:  

Genes are Sometimes Linked

-Certain alleles are almost always expressed together

-Linked genes are on the same chromosomes and do not assort  independently

Polygenic Inheritance

-Traits can be controlled by multiple factors

-Epistasis-Lab coat color determined by 2 genes that interact

-Without knowing gene type, it is impossible to know dog color -Sickle cell anemia

-Multiple effect of one gene-decreased ability to transport oxygen but  decreases susceptibility to malaria

Dominance is Not Always Complete

-Incomplete dominance: Parental phenotypes blend in the heterozygote -Blending ends with the heterozygote

-Co-dominance-heterozygotes show both parental phenotypes unblended -Dominance is not always complete co-dominance

Environmental Differences’ Effect on Factor Expression

-Siamese cats- melanin in Siamese cats is due to temperature- near core,  temperature is too high to allow expression of melanin-producing enzyme

Chromosomes:

Terminology:

Karyotype-Map of set of chromosomes

Chromatids-When chromosomes condense & become visible but before they  replicate

Sister Chromatids-The two identical chromatid copies formed during replication Centromere-Part of the chromosome that links sister chromatids Chromosome-Pair of sister chromatids form the chromosome Homologous Pair-Same chromosome type from mom and dad  

Mitosis

-Interphase

-DNA is diffused and hard to see

-Phase where DNA is replicated

-Only phase of cell cycle where DNA is accessible to proteins involved in  replication

-Prophase

-Mitosis begins

-Chromatin becomes more compact & becomes visible

-Now consist of identical sister chromatids

-Mitotic spindle forms-structure that will pull the cell apart

-Prometaphase

-Nuclear envelope breaks down

-Kinetochore microtubules, which are connected to the poles, attach to the  chromosomes

-Metaphase

-Chromosomes line up at mid-line of cell-Equatorial position

-Chromosomes are condensed and highly quarreled  

-Anaphase

-Sister chromatids are pulled apart to opposite ends of the cell

Telophase

-Last phase of mitosis

-Chromosomes are fully separated

-Cell cleaves in half to form two daughter cells

-Daughter cells have same number of chromosomes as parent cell-identical  copies

Meiosis:

-Following interphase, chromosomes begin to condense and a meiotic  spindle forms

-Homologous pairs join in center of cell

-Each chromosome will end up at each end of the cell

-Cell divides to form 2 daughter cells

-Daughter cells are genetically distinct & have only half as many  chromosomes as parent cell (when gametes join, there will be the right  number of chromosomes)

Ploidy=number of copies of chromosomes

A cell with one copy is a Haploid (1N)-Gametes

Cell with 2 copies is a Diploid (2N)

More than two copies is a polyploidy (xN)

Mitosis:

2N????4N????2N

Meiosis:

2N????4N????2N????1N

Crossing Over

-Occurs in the beginning of meiosis when homologous pairs join -Enzymes break & rejoin chromatids on homologous chromosomes-DNA from non sister chromatids can be exchanged

-Now chromosomes from dad may have DNA from mom’s chromosome on it -Chromosomes may have many or very few crossovers

Recombination

-Now genetic material from parents is mixed-leads to much higher variation among  offspring

Gene Linkage

-When genes are unlinked, the F1 generation can produce gamete combinations -When traits are linked A will not appear with b and B will not appear with a -Distance between genes on chromosomes has a lot to do with whether or not they  will be linked

-Genes close together on chromosome are tightly linked, while genes further  apart are loosely linked as they can be easily separated during recombination

DNA

-Double helix-two strands of genetic material (Discovered thanks to Rosalind  Franklin’s X-ray of DNA)

-Backbone made up of repeating sugar and phosphate units

-H-bonds hold nucleotides together-specifically pair certain nucleotides together Four nucleotides:

-Adenine (A)-pairs with Thymine

-Thymine (T)

-Cytosine (C)-Pairs with Guanine

-Guanine (G)

Semiconservative DNA Replication- Produces molecules with both old and new  DNA, but each molecule contains one complete old and one complete new strand -Due to complimentary pairing, information of strands is rarely lost  -Helix unzips original strand, breaks bonds between nucleotides and enzymes work  together to bring new nucleotides to parental chain & form daughter strands -DNA Polymerase matches existing nucleotides on parental chain with  complimentary bases & form bonds between the new pairs

Transcription

-Process of copying DNA to RNA

-Replication and transcription occur in the nucleus

Translation-RNA to proteins

-Occurs outside the nucleus

RNA

-Always single stranded

-Adenine pairs with Uracil rather than Thymine

Protein

-Made up of amino acids

-All proteins are different combinations of only 20 amino acids

-Codons-3-letter units that encode amino acids

-Some codons stop translation

Allele Frequency 

-Allele frequency is simply the number of times that an allele occurs in a population

How do Allele Frequencies change?

1.) Gene flow

a. Migration of alleles from one population to another

2.) Non-random mating

a. Assortative mating-organisms of similar phenotypes tend to mate  together more often than expected by random chance

b. Increases homozygous organism ratio

3.) Genetic Drift

a. Random changes in allele frequencies-has bigger effect in small  populations

b. Founder Effect-When a portion of a population becomes separated  and interbreeds to form new allele frequencies

c. Bottleneck Effect-When a natural disaster wipes out the majority of a  population. The remaining survivors will reproduce to create new,  less diverse allele frequencies (Finches on Daphna Major island) 4.) Mutation

a. Ultimate source of genetic variation, though not a driving force in  changes to allele frequencies

b. Findings of Francis Crick & Sydney Brenner:

i. -Codons are not spaced and read in threes

ii. -Reading frame is critical

c. Point Mutations:

i. Frame-Shift Mutations-disastrous effects, causes entire chain  of amino acids to be translated incorrectly

ii. Silent Mutations-also called synonymous substitution-no  

change in amino acid sequence

iii. Missense Mutations-also called non-synonymous substitution occurs when one amino acid is replaced by another

iv. Nonsense Mutations- Substitution of a base by a stop codon early termination of translation almost always results in the  

loss of function for the protein

d. Chromosomal Mutations:

i. Deletion-when large chunk of chromosome is deleted, causes a  significant loss of genes

ii. Duplication-when a large region of the chromosome is copied iii. Inversion- when a section of the chromosome is reversed &  placed back into the chromosome. So long as this does not  

happen in the middle of a gene, it usually has no effect

iv. Translocation-when a piece of chromosome attaches to it’s  

non-homologous pair during crossing over

Meiosis  

Nondisjunction

-Occurs when chromosomes fail to separate during metaphase  

1

Aneuploidy 

-Have gained or lost a chromosome

-Very common in sex chromosomes (5% of conceptions)

-Klinefelter’s syndrome: XXY

-Turner’s Syndrome: XO

-Monosomy- when a gamete has lost a chromosome-fatal

-Trisomy-gamete with an extra chromosome (occasionally individuals  can survive this)-Down Syndrome –extra chromosome

Polyploidy 

-Entire genome is copied

-Can be caused by meiotic error where homologous chromosomes do  not separate or can be result of hybridization between 2 different  species

-Rarely happens in animals & is often fatal if it does occur

-Extremely common in plants

-Bananas have 3 sets of chromosomes rather than 2

5.) Natural Selection

Factors required for Natural Selection to Operate:

-Must be variation in the population

-Variation must lead to differences among individuals in lifetime  reproductive success

-Variation must be transmitted to the next generation

Common Selective Forces

1.) Predation

2.) Climatic factors

3.) Parasitism

4.) Mate Attraction

5.) Resource acquisition

Stabilizing Selection 

-When just one variation of a trait works best for the species

-Decreases range of traits found in a population so that all species are closer to a  mean value

Directional Selection 

-When the environment changes, mean for a trait moves higher or lower Disruptive Selection

-Where extremes exist for each trait range, but there is a very low percent of  population near the mean

Balancing Selection  

-Heterozygote advantage

-Sickle-cell anemia-heterozygote has advantage of malaria immunity that  homozygotes do not

-Negative Frequency dependent selection

-Fitness of a species becomes higher as the frequency of its genotype  increases

-Rare individuals have a higher fitness than common individuals  -Maintains polymorphisms among prey species-rare species is less likely to  be recognized by predators

Sexual Selection

-Traits are selected purely because they attract better mates

Reproductive Strategies:

-Mate choice

-Mating frequency

-Mate guarding

-Long-term mating behavior (monogamy vs. polygyny)

-Parental care

-Offspring spacing

Females are Selective:

-Females invest far more in reproduction

-Energy-Human eggs are 195,000x larger than sperm and contain far more nutrients -Time-Gestation and child rearing leave females to deal with their choices for years

While Females Choose, Males Compete

-Competition through aggression or display-over access to females -Sexual dimorphism-males have special characteristics like horns and antlers for  fighting, and elaborate display characteristics (peacock feathers)

In Absent Fathers, Females look for:  

-Oldest, largest & healthiest males

-All of these traits show good genes, clearly the male has been able to survive  & support himself for a long time

Handicap Principle

-Males show off characteristics that are actually a handicap to their survival -If a male bird has to carry around a huge set of healthy tail feathers (a  handicap to him), he must be especially fit

Runaway Selection

-Elaborate & exaggerated male ornamental features that no longer serve a  practical purpose for survival

-Natural selection will eventually stop runaway selection, as impractical  traits will lead to lower fitness

Speciation

-When all small evolutionary changes add up to a big evolutionary moment Allopatric: Occurring in separate, non-overlapping geographical areas

Sympatric-Occupying the same overlapping geographic areas

Prezygotic Isolating Mechanisms:

1.) Geographic: species from different locations do not mate, as they do not interact  2.) Behavioral: during the selection of a possible mate, individuals from different  species may discard each other, as they don’t have the same mating rituals. 3.) Temporal: individuals from different species may mate at different times of the  year

4.) Mechanical: different species may have different sex organs, which are not  compatible

5.) Gametic: Chemicals In this case gametes won’t recognize each other and  fertilization won’t take place.

Postzygotic Isolation

1.) Hybrid viability: sometimes the hybrid dies prematurely.

2.) Hybrid fertility: even if an offspring is produced from the mating of different  species usually they are infertile as they generally have a random mixed number of  chromosomes (so it’s not the same even between hybrids).

3.) Hybrid breakdown: if the hybrid results to be fertile, the hybrid population might  breakdown over time (offspring may be less fertile)

“Missing Link” Isolation

-Intermediate populations that link 2 populations together go extinct, the gene flow  between 2 populations is cut off

Monophyletic vs. polyphyletic vs. paraphyletic Phylogenies

Source: http://www.mun.ca/biology/scarr/139417.jpg 

Parsimony-phylogeny that requires the fewest independent evolutionary events