Evolution Flashcards
Causes of variation
- random assortment
- crossing over
- non-dysjunction
- random fertilisation
- mutation
Random Assortment
chromosomes sorted into daughter cells randomly; many possible combinations of chromosomes coming from both mother and female
Crossing Over
Homologous pairs exchange different segments of genetic material
Non-dysjunction
Failure of chromatids to separate during meiosis
Random fertilisation
Any sperm can fertilise any ovum
Mutations
Permanent changes in the DNA - may result in new characteristics
Species
Organisms with shared characteristics that can produce fertile offspring
Population
A group of organisms of the same species living in a particular place at a particular time
Gene pool
The sum of alleles in a given population - can change over time (increase/decrease)
Allele frequencies
Measured in % - shows the frequency of a certain trait in a population
Allele frequency of cystic fibrosis
95% of population don’t carry CFTR gene - 5% frequency of cystic fibrosis allele
Evolution
Gradual change in phenotype thought to be caused by a change in allele frequency
Causes of Changes to Allele frequency
- Mutations
- Natural Selection
- Random Genetic Drift
- Migration
- Barriers to Gene Flow
- Genetic Diseases
Random mutations
Only a small section of DNA is affected, altering a single gene
Chromosomal mutations
many genes or the entire chromosome is affected
Somatic mutations (random mutations)
body cells experience mutation - dies out with organism
Germline mutations (random mutations)
Offspring from the affected gamete will inherit the gene; the individual is unaffected
Natural selection
Selection pressures make traits more favourable for survival - passed onto offspring
Random Genetic Drift
Usually only occurs in small populations - by chance, allele frequency changes (the traits aren’t advantageous)
Examples of Random Genetic Drift
Dunkers - small religious groups in Germany only intermarry; allele frequencies for blood groupings, mid-digital hair, ear lobes and handedness are different to the general population
Founder Effect
Allele frequency of emigrating group is different from the original population (Islander population vs Mainland)
Achromatopsia
Inherited total colour blindness - only 20 people survived following typhoon on Micronesian Island; allele frequency high
Migration
The gene flow from one population to another - individuals joining the population change the allele frequencies
Barriers to Gene Flow
Prevent interbreeding between populations - isolated population may be subjected to different environments with different selection pressures = different gene pools
Genetic Diseases
Expected that the frequency of a disease allele will decrease in population over time
Tay-Sachs Disease
Recessive autosomal disease
Homozygotes lack enzyme = build up of lipids in NS, die by 5 - high in Jewish populations because heterozygotes have immunity to tuberculosis
Sickle Cell anemia
Allele frequency high in African countries - heterozygotes have resistance to malaria
Natural Selection - Observations
- variation exists
- birth rate exceeds resource avaliability
- Nature’s balance - high birth rates, yet populations are stable
Struggle for existence
Organisms with variations that best suit their environment will survive
Speciation - steps
- variation (exists)
- isolation (occurs)
- selection (occurs)
- speciation
Speciation
Resulting changes in gene frequencies make it impossible for the two groups to interbreed
Effect of evolution
increase in the frequency of advantageous alleles, decrease in the frequency of disadvantageous alleles
Evidence for evolution
- fossils
- comparative studies
- geographical distribution
Comparative studies
Comparative biochemistry & comparative anatomy
Comparative biochemistry
DNA
Mitochondrial DNA
Protein sequences
Genomics
Comparative anatomy
Embryonlogy
Homologous structures
Vestigial organs
Comparative biochemistry - theory
Supports the ida that organisms are related to each other (share common ancestor) - gradual differences in DNA as organisms become more distantly related
Junk DNA
Non-coding DNA; the more closely related organisms are, the more junk DNA they have in common
Endogenous Retroviruses (ERV)
Viral sequence becomes part of organisms DNA (junk) - makes up 8% of genome; distant relations have less ERV in common
Mitochondrial DNA
Inherited through the maternal line
Has a higher number of mutations than nuclear DNA’ the number of mutations is proportional to the amount of time passed
Protein sequences
animals from the same species have identical aa proteins in DNA; degree of similarity determined by comparing the type and sequence of amino acids
Ubiquitous proteins
carry out the same function in all animals (cytochrome c)- supports the theory of the common ancestor
Comparative genomics
differences and similarities between genomes determine relationship
Embryology
study of embryo and its growth; all vertebrate embryos has gill arches and sacs, lack appendages and substantial tails
Homologous structures
Organs that are a similar structure but used for different functions (front limb)
Vestigial organs
Structures of reduced size that have no function (nictating membrane, hair on body)
Geographical dating
Isolated regions lead to unique characteristics that suit their environment
Eg. Finches on Galapagos, marsupials in Australi
Fossils
Any preserved trace or evidence left by a previously living organism
Teeth, footprints, faeces, burrows, egg shells
Fossil Formation
- A quick burial of remains
- The presence of hard body parts
- An absence of decay organisms (bacteria)
- Long period of stability
Drifting sand, mud, volcanic ash enhances fossil formation
Alkaline soils
Wet, acid soils with no oxygen = complete preservation of bones and tissues
Absolute Dating
The actual age of the fossil
Radiocarbon dating, potassium-argon dating, tree ring dating
Radiocarbon dating
Method based on the decay of C14 to nitrogen
N14 enters the atmosphere; decays to C14
Vegetation use C14 in photosynthesis
Other organisms eat vegetation – enters body
After death, C14 decays
C14 is measured to determine the absolute age of organism
Radiocarbon dating - positives
Absolute form of dating
Only form of dating for organic matter
Radiocarbon dating - negatives
Requires 3 grams of organic material
Cannot date past 60 000 years
Potassium-Argon dating
Measuring the amount of potassium compared to calcium and argon
- Young = ↑ K
- Old = ↓ K, ↑Ca, Ar
Potassium-Argon dating - positives
Only method to date rocks
Dates really old things; 200 000 years old
Potassium-Argon dating - negatives
Hard to date young rocks – ½ life is long
Only date igneous rocks
Tree ring dating
Study concentric rings on tree trunk to determine age and growing conditions of season
Tree ring dating - positives
Provides accurate dates as far back as 8600 years
Easy to read
Can be used to relative date civilisation
Tree ring dating - negatives
Trees can be destroyed
Only useful is
Relative dating
determining age of fossil compared to something else
Stratigraphy, fluorine dating
Stratigraphy
Deeper layers are older
Affected by folding, faulting, and erosion
Index fossils
Widely distributed for a short period of time (pollen)
Fluorine dating
Comparing the amount of fluorine ions in the fossil - over time other particles in the fossil are replaced by fluorine
Relative because fluorine levels vary from place to place and time to time
Binomial nomenclature
All organisms are named according to their genus and species
Homo sapiens
Pongids – Orang-utan
Gorillini – Gorilla
Panini – Chimpanzee
Primates are animals belonging to the Order primate
Primate Characteristics (15)
Unspecialised body Unspecialised limbs Pentadactyl Grasping digits with friction ridges Opposable first digit Forward facing eyes (stereoscopic vision) Colour vision Reduced sense of smell 4 incisors in top and bottom jaws Relatively large and complex brain Larger cerebrum in more complex primates Can reproduce throughout the year Rhythmical sexual cycle Usually one offspring at a time Long period of parental care
Changes in characteristics - evolutionary trends
Digits, cerebral cortex, vision, gestation and parental care, dentition
Evolutionary trends - digits
5 digits; high mobile due to arboreal ancestry
Digits are prehensile
Thumbs are opposable and independent
Humans lack opposable toe
Nails instead of claws - easier to grasp
Friction ridges increase grip
Old world monkeys and humans have a precision grip
Evolutionary trends - vision
With evolution, face become flatter, cranium becomes larger
Forward facing eyes allow stereoscopic vision
Also led to a narrow field of vision – compensated for with a highly mobile neck
Rods and cones in retina – rods allow vision in dim light, cones deal with fine visual discrimination and colour vision
Evolutionary trends - cerebral cortex
Responsible for complex functions
Vision, memory, reasoning, manipulative ability
Larger cerebral cortex = more accurate visual and tactile perception, better coordination
Number of cerebral convolutions increases with evolution
Tool making over tool use
Behavioural responses – grooming, allies, enemies
Evolutionary trends - gestation and parental care
Not restricted to limited reproductive season – rhythmical
Long periods of parental care
Apes and humans have a very effective placenta
Longer gestation period = brain development
Long parental care; delayed maturation, attain sexual maturity later
Long maturation gives long period of learning
Prolonged parental care increases survival chances
Evolutionary trends - dentition
More cusps on molars – 5 on humans
Less teeth
Flattened teeth
Diastemma appear – OWM
Hominids
homo sapiens, panini, gorillini, pongid
Homininae
gorillini, panini, homo sapiens
Hominins
homo sapiens and caveman ancestors
Greater apes
Larger overall body size, less pronounced arm:leg difference, larger brains, prominent facial features, omnivores
Orang utans, gorilla, chimpanzee
Lesser apes
Smaller, long and thin arms, vegetarian
gibbons and siamangs
Adaptations
characteristics that help an organism to survive and reproduce in its natural environment
Human adaptations
position of foreman magnum, jaw size, spinal curvature, pelvis, carrying angle, the knee, foot arches, centre of gravity,
Position of foreman magnum - adaptation
Directly under the skull in humans
In quadrupeds, it’s further to the back of the head
Allows it to balance on top of the vertebral column
Non-humans have much stronger neck muscles
Spine curvature - adaptation
Double curvature; s-shaped spine
Curves bring the head directly over the hips
The centre of gravity runs straight through the head and spine
Jaw size - adaptation
Human jaw is smaller and less prognatic
Allows skull to balance on the spine – weight in front of foramen magnum is approximately the same as the weight behind it
Pelvis - adaptation
Hip joint is directly under the head and trunk
Supports the abdominal organs during upright stance
Broad hip bones provide space for large buttock muscles to attach
Carrying angle - adaptation
The carrying angle ensures weight distribution remains close to the central axis
Femurs converge towards knees
Enables body to rotate about lower leg and foot – produces striding gait
Weight transmitted through outside of femur
The knee - adaptations
Weight is transmitted down outside of the femur to the knee
No energy required to support body in standing position – ligaments naturally resist bending backwards
The foot - adaptations
Human foot doesn’t have an opposable toe No longer prehensile Longitudinal and transverse arch Non-humans only have a longitudinal arch Arches facilitate striding gait
Centre of gravity - adaptations
centre of gravity
Allows greater stability during striding
Longer legs facilitate longer steps when striding
Stance and locomotion - adaptations
Distinguishing feature is striding gait
Muscle tone; Partial contraction of many skeletal muscles
Facilitates posture
Requires sustained muscle tone
Supports upright stance; spine, hip, knee, ankle, abdomen
Nervous system and sense organ work together to maintain postural equilibrium
Striding gait – hip and knee are fully extended
Weight is distributed from heel to ball of foot, then through big toe
Big toe is parallel – for weight bearing rather than grasping
Trunk rotates about pelvis – arms swing in opposite direction to reduce energy
Carrying angle allows body to rotate about the lower leg and foot
Tool culture trend
With evolution, tools become more refined; sharper, made with more detail and more flakes removed
Oldowan Tool
(pebble tool) Used by homo habilis, used by Australopithecines
Simple, crudely fashioned - round cobble with top knocked off
Used to exploit environment; hunting fish, sharing food
Acheulian Tool
(hand axe) used by homo erectus
Usually ‘tear drop’ shape, many more flakes removed than oldowan tool
Pointy top and wide flat base
Butchering large game, scalping/removing skins & hides
Mousterian Tool
(Flake tool) used by neanderthal man
Smaller flakes removed, spear heads attached to wooden shaft
Used to prepare animal hide to make specific clothes and tents
Upper Palaeolithic tools
(blade tools) used by homo sapien, cromagnon man
Sharper, pointer, different materials used (ivory)
hunting, ornamental; tools were specific (hooks, needles)
Old World Monkey
Closer to modern man, better developed brain, sensitive fingerpads, rods and cones, larger in size, flat fingernails instead of claws
Either arboreal or on land
Rhesus monkey, baboons
New World Monkeys
Arboreal lifestyle, sharp claws, prehensile tail
Marmosets, spider monkey
Bipedalism - advantages
- Greater field of view
- Increased ability to deter predators due to increased height
- Hands are free for carrying/making tools
- Higher reach when picking fruit
- Increased cooling ability
