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Human Biology Unit 4 > Evolution > Flashcards

Flashcards in Evolution Deck (95):
1

Causes of variation

1. random assortment
2. crossing over
3. non-dysjunction
4. random fertilisation
5. mutation

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Random Assortment

chromosomes sorted into daughter cells randomly; many possible combinations of chromosomes coming from both mother and female

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Crossing Over

Homologous pairs exchange different segments of genetic material

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Non-dysjunction

Failure of chromatids to separate during meiosis

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Random fertilisation

Any sperm can fertilise any ovum

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Mutations

Permanent changes in the DNA - may result in new characteristics

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Species

Organisms with shared characteristics that can produce fertile offspring

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Population

A group of organisms of the same species living in a particular place at a particular time

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Gene pool

The sum of alleles in a given population - can change over time (increase/decrease)

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Allele frequencies

Measured in % - shows the frequency of a certain trait in a population

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Allele frequency of cystic fibrosis

95% of population don't carry CFTR gene - 5% frequency of cystic fibrosis allele

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Evolution

Gradual change in phenotype thought to be caused by a change in allele frequency

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Causes of Changes to Allele frequency

1. Mutations
2. Natural Selection
3. Random Genetic Drift
4. Migration
5. Barriers to Gene Flow
6. Genetic Diseases

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Random mutations

Only a small section of DNA is affected, altering a single gene

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Chromosomal mutations

many genes or the entire chromosome is affected

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Somatic mutations (random mutations)

body cells experience mutation - dies out with organism

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Germline mutations (random mutations)

Offspring from the affected gamete will inherit the gene; the individual is unaffected

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Natural selection

Selection pressures make traits more favourable for survival - passed onto offspring

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Random Genetic Drift

Usually only occurs in small populations - by chance, allele frequency changes (the traits aren't advantageous)

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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

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Founder Effect

Allele frequency of emigrating group is different from the original population (Islander population vs Mainland)

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Achromatopsia

Inherited total colour blindness - only 20 people survived following typhoon on Micronesian Island; allele frequency high

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Migration

The gene flow from one population to another - individuals joining the population change the allele frequencies

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Barriers to Gene Flow

Prevent interbreeding between populations - isolated population may be subjected to different environments with different selection pressures = different gene pools

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Genetic Diseases

Expected that the frequency of a disease allele will decrease in population over time

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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

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Sickle Cell anemia

Allele frequency high in African countries - heterozygotes have resistance to malaria

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Natural Selection - Observations

1. variation exists
2. birth rate exceeds resource avaliability
3. Nature's balance - high birth rates, yet populations are stable

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Struggle for existence

Organisms with variations that best suit their environment will survive

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Speciation - steps

1. variation (exists)
2. isolation (occurs)
3. selection (occurs)
4. speciation

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Speciation

Resulting changes in gene frequencies make it impossible for the two groups to interbreed

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Effect of evolution

increase in the frequency of advantageous alleles, decrease in the frequency of disadvantageous alleles

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Evidence for evolution

1. fossils
2. comparative studies
3. geographical distribution

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Comparative studies

Comparative biochemistry & comparative anatomy

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Comparative biochemistry

DNA
Mitochondrial DNA
Protein sequences
Genomics

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Comparative anatomy

Embryonlogy
Homologous structures
Vestigial organs

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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

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Junk DNA

Non-coding DNA; the more closely related organisms are, the more junk DNA they have in common

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Endogenous Retroviruses (ERV)

Viral sequence becomes part of organisms DNA (junk) - makes up 8% of genome; distant relations have less ERV in common

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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

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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

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Ubiquitous proteins

carry out the same function in all animals (cytochrome c)- supports the theory of the common ancestor

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Comparative genomics

differences and similarities between genomes determine relationship

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Embryology

study of embryo and its growth; all vertebrate embryos has gill arches and sacs, lack appendages and substantial tails

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Homologous structures

Organs that are a similar structure but used for different functions (front limb)

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Vestigial organs

Structures of reduced size that have no function (nictating membrane, hair on body)

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Geographical dating

Isolated regions lead to unique characteristics that suit their environment
Eg. Finches on Galapagos, marsupials in Australi

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Fossils

Any preserved trace or evidence left by a previously living organism
Teeth, footprints, faeces, burrows, egg shells

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Fossil Formation

1. A quick burial of remains
2. The presence of hard body parts
3. An absence of decay organisms (bacteria)
4. 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

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Absolute Dating

The actual age of the fossil
Radiocarbon dating, potassium-argon dating, tree ring dating

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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

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Radiocarbon dating - positives

Absolute form of dating
Only form of dating for organic matter

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Radiocarbon dating - negatives

Requires 3 grams of organic material
Cannot date past 60 000 years

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Potassium-Argon dating

Measuring the amount of potassium compared to calcium and argon
- Young = ↑ K
- Old = ↓ K, ↑Ca, Ar

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Potassium-Argon dating - positives

Only method to date rocks
Dates really old things; 200 000 years old

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Potassium-Argon dating - negatives

Hard to date young rocks – ½ life is long
Only date igneous rocks

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Tree ring dating

Study concentric rings on tree trunk to determine age and growing conditions of season

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Tree ring dating - positives

Provides accurate dates as far back as 8600 years
Easy to read
Can be used to relative date civilisation

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Tree ring dating - negatives

Trees can be destroyed
Only useful is

60

Relative dating

determining age of fossil compared to something else
Stratigraphy, fluorine dating

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Stratigraphy

Deeper layers are older
Affected by folding, faulting, and erosion

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Index fossils

Widely distributed for a short period of time (pollen)

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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

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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

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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

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Changes in characteristics - evolutionary trends

Digits, cerebral cortex, vision, gestation and parental care, dentition

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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

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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

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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

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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

71

Evolutionary trends - dentition

More cusps on molars – 5 on humans
Less teeth
Flattened teeth
Diastemma appear – OWM

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Hominids

homo sapiens, panini, gorillini, pongid

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Homininae

gorillini, panini, homo sapiens

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Hominins

homo sapiens and caveman ancestors

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Greater apes

Larger overall body size, less pronounced arm:leg difference, larger brains, prominent facial features, omnivores
Orang utans, gorilla, chimpanzee

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Lesser apes

Smaller, long and thin arms, vegetarian
gibbons and siamangs

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Adaptations

characteristics that help an organism to survive and reproduce in its natural environment

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Human adaptations

position of foreman magnum, jaw size, spinal curvature, pelvis, carrying angle, the knee, foot arches, centre of gravity,

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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

80

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

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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

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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

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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

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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

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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

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Centre of gravity - adaptations

centre of gravity
Allows greater stability during striding
Longer legs facilitate longer steps when striding

87

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

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Tool culture trend

With evolution, tools become more refined; sharper, made with more detail and more flakes removed

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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

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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

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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

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Upper Palaeolithic tools

(blade tools) used by homo sapien, cromagnon man
Sharper, pointer, different materials used (ivory)
hunting, ornamental; tools were specific (hooks, needles)

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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

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New World Monkeys

Arboreal lifestyle, sharp claws, prehensile tail
Marmosets, spider monkey

95

Bipedalism - advantages

1. Greater field of view
2. Increased ability to deter predators due to increased height
3. Hands are free for carrying/making tools
4. Higher reach when picking fruit
5. Increased cooling ability