Evolution and Biodiversity/ Genetics and Evolution Flashcards
1
Q
Charles Darwin:
A
Traveled on the HMS Beagle for 5 years for scientific exploration in 1831 to the Galapagos
Came up with the idea of evolution by Natural Selection
1858: Alfred Russel Wallace independently also develops similar theory; they work together
2
Q
Evolution:
A
Evolution: the process of cumulative change in the heritable characteristics of a population
3
Q
Heritable
A
Heritable: changes must be passed on genetically from one generation to the next
4
Q
Cumulative
A
Cumulative: stresses the fact that one change is not enough to have a major impact on a species; changes don’t just affect one individual but a whole population
5
Q
Speciation:
A
Speciation: when a new species arise when enough changes occur within a population that the new species can no longer interbreed with the old
6
Q
Fossil Record
A
Fossils: petrified remains/traces of animals and plants
Fossil record: accumulation of evidence from these remains/traces
e.g. skeletons and footprints
7
Q
Discoveries by Palaeontologists regarding evidence for Earth’s evolutionary past:
A
Life existed more than 500 million years ago was very different from today
Although the Earth has extensive oceans, fish fossils have only been found in rocks 500 million years old/younger (less than 15% of the 3.5 billion year existence of life on the planet)
Top predators of today (bears, orcas, wolves) didn’t exist at the time of dinosaurs/before
Majority of living organisms today have no similar form in the fossil record
Main conclusion: life on earth is constantly changing over huge timescales
8
Q
Isotopes
A
versions of atoms that are heavier/lighter than others
9
Q
Radioactive decay
A
process of a radioactive parent isotope changing into a stable daughter isotope
10
Q
Isotope’s half-life
A
speed at which radioactive decay occurs (time it takes for half of the parent isotope to decay into a stable daughter isotope)
11
Q
ageing fossils
A
Age of rocks/fossils determined by difference of the ratios of isotopes
Fossils with high Carbon-14 levels are younger than bone/shell with low levels
Carbon 14 is radioactive but loses its radioactivity as it gives it off; changes its identity into another atom (Nitrogen -14) RADIOACTIVE DECAY
12
Q
Why is radioactive decay important?
A
Ratios of radioactive isotopes (C14 to N14) tells us the age of the fossil
E.g. If there is 12.5% of the radioactive isotope and 87.5^ of the stable isotopes that means that there are three half-lives and the fossil is 17 190 years old
HOWEVER; after a certain number of half lifes, there are few radioactive isotopes so it’s difficult to determine the fossil age with accuracy
BUT there are other radioactive isotopes (potassium-40) that have longer half-lives that can be used
13
Q
How can age of rocks be determined?
A
Using Radiometric techniques with 40K to measure the age of rocks formed from magma or lava between 100 000-4.6 billion years ago
14
Q
SELECTIVE BREEDING;
A
SELECTIVE BREEDING; farmers/breeders realize that certain varieties of animals have unique combinations of characteristics that didn’t exist previously
E.g. meat or milk is different than that from a few generations ago
15
Q
Artificial Selection + Evolution
A
Science of breeding domesticated animals provides a good record of recent changes in heritable characteristics
Animal breeders can see value of the offspring’s characteristics by mating animals
Breeders learn to choose males + females with most desirable genetic characteristics and breed them
16
Q
ARTIFICIAL SELECTION;
A
Evidence for evolution based on human choice=
ARTIFICIAL SELECTION; not the driving force of evolution in ecosystems as it is based on human intervention/choice
17
Q
Evolution of homologous structures by adaptive radiation;
A
Homologous anatomical structures provide evidence for evolution in dissimilar species
E.g. Five-fingered limb found in animals such as humans, whales and bats; it’s called the pentadactyl limb
general format of pentadactyl limb the same, even though functions may vary
Darwin explains that homologous structures aren’t a coincidence but evidence that these organisms have a common ancestor (all pentadactyl organisms have common ancestry)
Show varied morphology!
18
Q
Species
A
Species: must be able to freely interbreed with members of the same species to produce fertile offspring
19
Q
Species divergence
A
Process of an evolving population changing significantly so that the production of offspring within a population becomes impossible
E.g. two populations have diverged and a new species evolves from an old one
20
Q
Adaptive Radiation:
A
occurs when many similar but distinct species evolved relatively rapidly from a single species/small number of species
21
Q
why does adaptive radiation happen
A
Variations within a population allow certain members to exploit a slightly different niche more successfully
22
Q
Niche:
A
Niche: position or role within a community of an ecosystem
23
Q
How does a new species evolve?
A
By natural selection and presence of some kind of barrier (e.g. mountain range or body of water)
24
Q
examples of adaptive radiation
A
- lemurs in madagascar
- Darwin’s finches on Galapagos Islands
-Hawaiian Honeycreepers
Different adaptations of the beak shapes; some for sipping nectar in flowers on Hawaii
25
explain the adaptive radiation in madagascar lemur species
Lemurs on Madagascar + Comoro Islands; had little competition so a they proliferated a lot
This produced a large variety of offspring with high diversity changes
Some adapted for living on ground instead of trees, while others adapted betwen living in rainforests or deserts
Some lemurs are diurnal others are nocturnal
So many species of lemurs with different specialities= adaptive radiation
No other lemurs in the world; but hey have fossil records in Africa, Europe and Asia= Lemur’s unsuccessful in competing with apes + monkeys; lemur-like organism becomes rare
Explains why continents/islands have prosimians (such as lemurs) or anthropoids (such as monkeys and apes) but not both types of primate
TODAY: lemur species becoming extinct/endangered due to anthropoid activity (human)
26
Continuous variation + gradual divergence:
| example
Saltmarsh grass; within a species that has a wide geographical distribution there can be DNA differences due the climate and soil being different
Saltmarsh cordgrass (Spartina alterniflora; provides habitat for organisms below and above water); three different plants from Massachusetts, Delaware and Georgia were taken
Hypothesis of Delaware experiment: if there is no genetic variation in species, then all three populations of plants from different latitudes will have similar growth patterns when grown in Delaware (given the same growing conditions of soil, water and light and temperature)
Results:
Southern georgian population grew the most (biomass, height and stem diameter= water warmer in south), whereas northern massachusetts population had least growth
Delaware population showed no difference in growth from other populations in delaware
Difference in growth refutes hypothesis; plants show similar patterns to native locations due to DNA influence (genetic variations in geographical locations)
27
Selective pressure:
populations adapt to the conditions available to them and some versions of genes will be selected for and others will be selected against so that the populations can best adapt to area
Tipping point; when differences outweigh similarities in two populations so they can’t reproduce anymore
E.g pollen from one species of marsh grass used to pollinate flowers from a southern population, and no seeds or fertile offspring were produced= speciation
28
Polymorphism:
different versions of a species that can be as a result of a mutation
29
Transient polymorphism
temporary changes in the form of a species due to environmental changes
30
example of (transient) polymorphism
```
Peppered moth lives in temperate climates;
Black moths (1% of population) vs white moths (black moths can be easily seen against light colored lichens + preyed upon by birds)
```
Industrial revolution caused change; black moths can now hide on black lichens therefore their population increased around urban/industrial areas
Clean air laws; promotes the return of light colored moths
31
Variation
There is variation in populations that results from reproduction
Variation is closely related to how successful an organism is (characteristics can aid it in surviving)
= Natural selection can only occur if there is variation amongst members of the same species
32
bacteria vs eukaryote
Bacteria are identical (unless mutations) whereas eukaryotes reproduce sexually therefore each offspring is genetically different
In contrast; bacteria have no difference in population, which means that if there is a large change in environment such as pH the bacteria can die
33
variation affects on alleles
An allele can change over time due to change in environment; only possible if there is more than one form of the allele within the population (e.g. peppered moths had a mutation which gave some a dark color and therefore aided the species in surviving the industrial revolution)
34
Mutation (as a source of variation)
Can cause genetic diseases which has bad effects
Beneficial mutations can however produce characteristics which aid the survival of a species (e.g. better camouflage for bird or insect)
In each generation, only a few mutations occur
Sexual reproduction is much more powerful source of variation in population due to mixing of genes
35
Meiosis:
| as a source of variation
Enables the production of haploid cells to make gametes
At the end of meiosis, four cells are produced that are genetically different from each other and only contain 50% of the patient’s genome
An individual that reproduces sexually produces large numbers of possible combinations of genes in offspring
Only identical offspring are twins
36
where does variation in meiosis come from
Process of random orientation during metaphase 1 (lining up of chromosomes in a random order promotes variety in gametes produced)
Process of crossing over; shuffling of genetic material in prophase I
Mixing of two gametes with 50% of parents genetic material (fertilization)
37
Sexual reproduction + variation
Asexual reproduction (binary fission) doesn’t promote variety
Natural selection only has two options; die or survive (problems of potato famine in Ireland; potatoes produced asexually and died due to infection)
Variety important to natural selection; more possibilities lead to more outcomes; some members of population survive adverse effects while others may be affected negatively (some individuals are adapted better to changes in environment than others)
Egg cell + Sperm cell + Chance= baby!
38
Sources of variation in a population
Mutations in DNA
Meiosis
Sexual reproduction
39
what type of adaptions are there
```
Adapting:
Conscious adaptations (made by individuals) vs. Unconconscious adaptations ( made by populations; evolution)
```
An organism that has characteristics that are well-adapted to its environment is said to be fit; characteristics it poses fit well into environment
40
adaption vs evolution
Organisms can adapt to change in environment within lifetime, this is not the kind of adaptation referred to an evolution (it’s adapted but not evolved)
E.g. peppered moths and giraffe neck adaptations
41
natural selection
Natural selection eliminated individuals in population with low fitness, and fittest individuals have higher likelihood of surviving
42
Too many offspring (pros and cons)
More offspring produced than could ever be produced (e.g. fish laying thousands of eggs, or mushrooms producing thousands of spores; only a few surviving to adulthood)
Paradoxical; production of many offspring needs a lot of energy/nutrients
However it maximizes the chances of offsprings surviving with a low survival rate if there are a lot of them
However many offspring= competition for resources and mates; produces adaptations in individual to find enough resources/mates; only ‘fit’ organisms can reproduce and pass on their traits
43
Adaptation and survival:
Limited resources= selection of the ‘fittest’ organisms that survive
Individuals survive based on surroundings + compatibility of their characteristics to the surroundings
44
Steps of evolution by natural selection:
1. Overproduction of offspring + natural variation as a result of genetic differences in those offspring
2. Useful variations allow some individuals to have a better survival chance
3. Harmful variations make it difficult to survive
4. Individuals with genetic characteristics that are poorly adapted for their environment tend to be less successful at accessing resources and have less chance of surviving to adulthood
5. Individuals with genetic characteristics that are well adapted for their environment tend to be more successful a accessing resources and have a better chance of surviving to maturity; better fitness
6. Because they survive to adulthood; they can reproduce and pass on their successful genetic characteristics
7. Over many generations; the accumulations of changes in heritable characteristics of a population results in gene pool change (EVOLUTION)
8. Individuals with HIGH FITNESS pass on their SUCCESSFUL TRAITS
9. 1Individuals with unsuccessfully traits (e.g. deformities) die off
45
example of fast natural selection
Pesticide resistance in rats and antibiotic resistance in bacteria= examples of natural selection
Mechanism of natural selection can be quick sometimes
46
Pesticide resistance in rats
Farmers use pesticide to eradicate rats to prevent them from eating crops
Some rats survive the pesticide due to natural variation; better adapted to living in fields and now have less competition for food and mates
Poison resistance gene is favoured so less rats die the next time the farmer uses pesticides
New pesticides must be developed
Immunity develops among lifetime of individual; pesticide resistance however is a change that evolves from one generation to the next (rat is either born with resistance or not)
Characteristics acquired during an organism’s lifetime cannot be passed onto next generation (don’t take part in evolution theory by natural selection)
47
antibiotic resistance in bacteria
Bacteria can mutate which makes some bacterial resistance to antibiotics
mutations/ modifications to genetic material of bacteria (Plasmid transfer)
Plasmid transfer involves on bacteria donating genetic information to another using plasmids to pass on resistant gene
Overuse of antibiotics leads to production of resistance straints
New antibiotics must be produced + people have to finish their terms
Doctors must minimize use of antibiotics + educate patients
48
SUMMARY OF EVOLUTION:
Evolution by natural selection
Involve chance (such as variation in population and sexual reproduction and gamete fertilization)
Natural selection favours useful adaptations against harmful ones; survival of the fittest
Heritable changes are passed on, so that each population adapts to its environment accordingly, and others die out
49
Binomial system for names of species
Binomial nomenclature (e.g. Homo sapiens)
First name is always capitalized and refers to genus
Second name begins with small letter and refers to species
Both are written in italics when typed, or underlined when written by hand
Most words come from latin or greek
Carl Linnaeus consolidated + popularized the system
50
Objectives of nomenclature system
1. To be sure that the organism has a unique name so it can’t be confused with another
2. Names must be universally understood regardless of nationality or culture
3. Stability must exist within system to not allow people to change names of organisms without valid reasons
51
naming rules
There is an “International Code of Zoological Nomenclature” that makes this rule
Scientists must refer to principle of priority of oldest valid publication of a name
International conferences discuss these naming tools
52
Naming new species:
Early days; only two kingdoms (plants and animals)
Nowadays; so many different types of kingdoms and species
Invention of the microscope aided in this
53
Examples of binomial nomenclature
Equus zerbra
Amoeba amazonas
Gekko geko
Gorilla gorilla
Paramecium caudatum
Laxadonta cylotis (African forest elephant)
Malus domestica (apple tree)
54
Rules for writing binomial nomenclature:
Genus name is capitalized while species name is not
Both written in italics/underlined
In addition, after these two names the last name of the person who first published the name in a scientific is given as citation
55
Taxa;
refers to the categories that scientists have generated names for
Used to classify species into many subcategories found in larger categories
56
Three domains of life:
Three domains of life:
Eukaryote: all life besides Archean and bacteria; membrane bound and membrane bound nucleus
Eubacteria; bacteria
Archean; single-celled organisms distinct from bacteria; live in diverse habitats
57
SEVEN principal taxa:
```
Kingdom
Phylum
Class
Order
Family
Genus
Specie
```
58
classify; HUMANS
```
Kingdom: Animalia
Phylum; Chordata
Class; Mammalia
Order: Primate
Family: Hominidae
Genus: Homo
Species: sapiens
```
59
classify; GARDEN PEA
```
Kingdom: Plantae
Phylum; Angiospermophyta
Class: dicotyledoneae
Order; Rosales
Family: Papilionaceae
Genus; Pisum
Species: sativum
```
60
Other classifications?
By feeding habitats; carnivore or herbivore?
By habitat; land dwelling or aquatic?
By daily activity; diurnal or nocturnal?
By risk; harmless or venomous?
By anatomy; vertebrate or invertebrate?
61
Linnaeus time;
Linnaeus time; existence and function of DNA unknown; classifications based on observable characteristics
62
Modern classificatio
Modern classification: based on ancestry and genetics
| Genetic similarities establish a genus (members of this genus have all evolved from a common ancestor)
63
what does the universal classification system allow
Universal classification system allows for scientific names to reveal evolutionary names between species
64
Reclassification:
Post-linnaean classification; DNA tech allows for some animals to be reclassified (some animals were put in same genus even though not related to another)
65
aster flower reclassifcation
Example: Aster flowers have different origins than their genus
Different types established, so reclassification required
Old classification: Aster cordifolius
New classification; Symphyotrichum cordifolium
66
Challenges of re-naming organisms:
Books and scientific journals have the old names
Prior to reclassification; must check that the name respects any recent reclassifications (use online resources)
Group of taxonomists decide change; doesn’t mean everyone agrees
Resistance in breaking tradition of name
67
Natural classification
Natural classification: uses ancestry to group organisms together
68
Artificial classification:
Artificial classification: use arbitrary characteristics
69
Why use natural classification?
Trying to make sense of biosphere
Showing evolutionary links
Predicting characteristics shared by members of a group
Make classification/discovery of new species easier
70
Bryophyta
includes plants of very short stature, such as mosses or liverwort.
Are referred to as non-vascular plants because they don’t have true vascular transport tissue inside of them (like xylem or phloem).
Produce spores (microscopic reproductive structures) that are transported by rainwater or ground humidity)
Found often on damp habitats such as forest floor.
71
Filicinophyta
includes ferns, horsetails, etc.
Vascular plants recognizable by the absence of flowers + their triangular fronts made up of smaller, long thin leaves.
Produce spores (microscopic reproductive structures) that are transported by rainwater or ground humidity)
Found often on damp habitats such as forest floor.
72
Coniferophyta:
includes cedar, juniper, fir and pine trees
Can be recognized by the fact that they all have woody stems and their leaves are in the form of needles or scales;
use wind as pollination method (produce seed cones with seed scales)
73
Angiospermophyta
plants that have flowers and seeds surrounded by fruit.
Don’t produce cones or are pollinated by wind; rely on pollinators such as birds, insects and mammals to transport pollen.
Sexual reproductive organs are flowers.
Fruits hold the seeds
74
Porifera:
Sponges; marine animals that are sessile (stuck in place), don’t have mouths or digestive tracts and pump water by filter feeding.
No muscle or nerve tissue or distinct internal organs
75
Cnidaria:
sea jellies and coral polyps., sea anemones, hydra, etc. All have stinging cells called nematocysts.
76
Platyhelminthes
flatworms; one body cavity, no heat or lungs.
| Non-segmented bodies; all cells need to be close to surface
77
Annelida
segmented worms, e.g. earthworms; their bodies are ringed
78
Mollusca
snails, clams, octopuses; aquatic with one-way digestive system. Unsegmented bodies but can have calcium enforced shells.
79
Arthropoda
Insects, spiders, crustaceans. Hard exoskeleton made of chitin, segmented bodies and limbs that can bend as they are jointed.
80
Chordata
Vertebrates (backboned animals). Have a notochord (spine) at some point in development. Most animals in this phylum (e.g. birds, mammals, amphibians, reptiles and fish)
81
VERTEBRATES:
- chordata phylum
82
Fish
Fish; aquatic organisms with gills and skulls made of bone or cartilage. Don’t have digit limbs.
83
Birds
Birds; Bipedal (2 legs), wings. Feathers and lay eggs with hardened shells. Hollow bones and jaws in the borm of beaks with no teeth. High metabolism rates and warm blooded.
84
Mammals;
Mammals; Foxes, hippos, squirrels, humans. Have hair on their bodies, females produce milk in specialized glands. Capable of thermoregulations
85
Morphology example
The shape of a plant’s seed coat or bird’s bill
86
Anatomy
| example
Number of petals on a flower or type of digestive system in invertebrate
87
Cytology
| example
Structure of cells or their function
88
Phytochemistry example
Special organic compound that only plants can make to protect themselves against insect attack
89
Chromosome number
| example
Two species with the same chromosome numbers are more likely to be related
90
Molecular differences example
Proteins and DNA sequences different between species
91
cladistics
system of classification that groups taxa together according to the characteristics that have evolved most recently; example of natural classification to decide how close a common ancestor is
92
Primitive traits (plesiomorphic
Primitive traits (plesiomorphic); characteristics that have the same structure and function + have evolved early on
93
Derived traits (apomorphic)
Derived traits (apomorphic): characteristics that have the same structure and function but that evolved recently due to modification
94
Biochemical evidence of clades
Biochemical evidence of clades;
| DNA and protein structures validate idea of common ancestor
95
Phylogeny;
Phylogeny; study of evolutionary past of a species
96
explain phylogeny process
Species more likely to be closely related if they are similar
One can compare the similarities in the polypeptide sequences of certain proteins and trace their ancestry (using blood protein haemoglobin with a mitochondrial protein called cytochrome C)
Advances in DNA sequence allows for biochemical phylogeny
97
Analogous traits:
Analogous traits: same function but don’t necessarily have the same structure and aren’t derived from a common ancestor. Wings as example of eagles, mosquitoes and bats not having same ancestor or fins in aquatic organisms
98
Homologous traits:
Homologous traits: the ones derived from the same part of a common ancestor; e.g. pentadactyl limbs in humans and bats or presence of eyes
99
Cladograms:
Represent ancestries and relationships between animals; show biochemical phylogeny
The clade is divided up into a sister group showing close relatives and an outgroup, showing less closely related to the others
Cladistics shows most logical and natural connections between organisms in order to reveal their evolutionary past; study of clades
Each cladogram is a working hypothesis; each time a derived characteristic is added to the list shared by organisms in a clade, the effect is to going up one level in the classification order
Reclassification changes clade diagrams
100
node
A node is the place where speciation happened and the common ancestor was found
101
figworts
Figworts used to be in Scrophulariaceae family as they were characterized by morphological features such as flower petals
Mid 1990S’ DNA analysis of plant classified in this taxon led to reclassification
Their DNA markers showed that they didn’t share a common ancestor with other Scrophulariaceae; they were paraphyletic (species on separate branches; analogical charcaterics)
Plants in the Scrophulariaceae family given new names; e.g. incorporated into Platiganacase family is foxgloves; no longer considered as figworts)
102
Prophase I
Process of synapsis brings together two homologous chromosomes in a pair called bivalent
Homologous means that the chromosomes have the same length, have their centromeres in the same position and contain the same genes at the same loci; difference is that one chromosome in the bivalent came from the mother and the other from the father
crossing over occurs
103
homologous chromosomes
chromosomes aren’t identical; have different alleles for each of the genes along the chromatids
104
sister chromatids
are identical as they come from the replication of the same chromosome during interphase
105
crossing over
mixing genetic material between nonsister chromatids (between paternal and maternal chromosomes) by chromatids intertwining to form a chiasmata and identical breaks occurring at same position + swapping genes in adjacent non-sister chromosomes
Two sets of bivalent chromosomes exchange genes (maternal and paternal pairs)
This leads to a new combination of alleles (dominant and recessive alleles changed)
106
Main ways that gamete production is able to generate genetic variety
Crossing over in prophase I
Random orientation during metaphase I
Independent assortment during metaphase I and II
107
Metaphase I:
Metaphase I:
Random orientation of bivalents and sister chromatids and independent assortment occurs
For humans; total number of possible combinations during random orientation is 223
108
Anaphase I;
Anaphase I;
| Homologous chromosomes separate as they are pulled to opposite sides of the cell
109
Anaphase II;
Anaphase II;
Sister chromatids are separated at the centromere splitting
Spindle microtubules pull individual chromatid to opposite sides of the cell
Due to random orientation, chromatids can be pulled to wards either of the newly forming daughter cells
110
Telophase I and II
Telophase I;
Chromosomes unravel and two cells form
Telophase II:
New nuclear membrane forms around four new cells each with a different combination of half the genetic material of the original parent cell
111
Independent assortment:
Gregor Mendel’s Law of independent assortment; states that when gametes are formed the separation of one pair of alleles between the daughter cells is independent of the separation of another pair of alleles (genes aren’t linked)
General rule: one allele doesn’t follow another when it is passed onto a gamete; implies that alleles that determine different characteristics will be transmitted independently to the next generation
112
exeption of independent assorment
linked genes
113
Monohybrid cross:
Monohybrid cross: examines only one genetic trait to see what kind of offspring two parents with different alleles can produce
114
Dihybrid crosses
Dihybrid crosses; take into account multi-genetic traits
| E.g. seed shape + color
115
Phenotype:
Phenotype: the resulting trait shown when a genotype is expressed
116
F1 and F2
F1: First generation and is the resulting offspring of the cross between the parents who are distinctly different
F2: Second filial generation that are the offspring of F1
117
Autosomes + Sex chromosomes:
Non- sex chromosomes
Make up 44 chromosomes (22 pairs) + the 2 sex chromosomes (1 pair of XX or XY)
Sex-linked traits are on sex chromosomes are are affected by the sex of the organism
118
Genetic disorders: Autosomal
Genetic disorders: Autosomal
Huntington's Disease; autosomal dominant gene on the fourth chromosome
Cystic fibrosis; caused by autosomal recessive gene on the 7th chromosome
Both disorders occur in similar proportions in male and females
119
Genetic disorders; Sex-Linked
Genetic disorders; Sex-Linked
| Colour blindness + Haemophilia; gene loci found on the X-chromosome and affect males more than females
120
Gene linkage:
Gene linkage:
Linkage groups; genes that are passed onto the next generation together; a group of genes inherited together because they are found on the same chromosomes
E.g. Body colour and wing length of the fruit fly genes are inherited together as the two genes are located on the same chromosome/loci
121
Recombinant genes:
Recombinant genes:
Occur through crossing over
Shuffling of alleles of genes creates a new combination that doesn’t match either of the parent’s genotypes
Gametes made up a bivalent will result in two containing combinations found in parents, and two with recombinants
Even in linked genes, there is variation
122
normal outcomes of genetic crossses
Outcomes of genetic crosses usually have a 3:1 ratio and 9:3:3:1 ratios (if these ratios don’t exist, it means there are recombinant genes and that independent assortment isn’t occurring because there are linked genes)
123
Polygenic inheritance:
Polygenic inheritance:
Two or more genes influence the expression one one trait
Number of possible genotypes increases when two or more genes are found on the same loci
E.g. Blood type
124
Continuous variation
Continuous variation: When an array of possible phenotypes can be produced e.g. human skin color as the intensity of pigment in skin is the result of the interaction of multiple genes
Continuous variation can be seen in genetic components of height, body shape and intellectual aptitude
125
multiple allues
Number of possible phenotypes is limited with dominant/recessive genes
Multiple alleles; increases number of possibilities for a single trait
E.g. ABO blood type has three alleles, and four possible phenotypes
126
Dis-Continuous variation (discrete)
unbroken transitional pattern from one group to the next. E.g. dry ear wax vs wet earwax (no in between) or blood type
127
polygenic characteristics
When there are many intermediate possibilities, the trait has continuous variation (results plotted on graph produce bell shaped distribution curve)
128
Gene pool
Gene pool: all the genetic information present in the reproducing members of a population at a given time (the larger the variation, the larger the gene pool)
129
Allele frequency
Allele frequency: measure of the proportion of a specific variation of a gene in a population
130
Evolution + gene pools
New alleles introduced as a result of mutation and alleles can disappear by organism dying; changes the gene pool
Some alleles aren’t passed on; aren’t fit
Populations can mix due to immigration/emigration; gene pool modified
131
Hardy-Weinberg equation
for determining the frequency of alleles/genotypes/phenotypes within a population
```
p2+2pq+q2= 1
p= frequency of dominant allele
q= frequency of recessive allele
```
132
Geographical isolation;
Geographical isolation; physical barriers (land or water) prevent males and females from breeding E.g. tree snails in hawaii cannot interbreed as they are on different sides of an island
133
Temporal isolation:
Temporal isolation: incompatible time frames/times of the year that the populations mate e.g. female parts of a flower or of a population reaches maturity at a different time than another or if mammal hibernating time doesn’t intersect
134
Behavioural isolation:
Behavioural isolation: when a population's lifestyle/habits/mating calls not compatible with another e.g. bird mating calls don’t attract others
135
Directional selection:
Directional selection:
When a phenotype is favoured over another by natural selection
Frequency of one phenotype increases as the other decreases
Often caused by environmental change e.g. industrial revolution for peppered moths
Selection away from one extreme to another
136
Stabilizing selection:
Stabilizing selection:
When one phenotype is favoured over two extreme phenotypes (middle)
E.g. Flower plant that makes a lot of nectar, however making a lot of nectar drains plant sugar sources= intermediate is the best
Selection away from two extremes/selection towards the mean
137
Disruptive selection:
Disruptive selection:
When two extreme phenotypes are favoured by natural selection, rather than one intermediate phenotype
Advantage of having two opposing phenotypes
E.g. tadpoles of spadefoot toads have either an omnivorous or carnivorous diet; two separate morphologies give species a better chance of surviving in places where water supply and food sources are variable
Selection against the mean; maintain two different phenotypes within population (it’s possible for speciation to occur)
138
polyploidy
Situation in which a cell contains three or more sets of chromosomes (3n, 4n, etc)
Such a situation can arise when cell division doesn’t completely separate the copies of chromosomes in distinct nuclei and they end up in the same cell (non-disjunction)
Extra sets of chromosomes; cause errors in replication
If one population of plants is triploid and another is tetraploid; each population's evolution will be different
Evolving population becomes so different= speciation happens
139
gradualism
1. Changes are small, continuous and slow (gradualism); supporters state that fossil records show a succession of small changes in the phenotype showing that it’s a steady, ongoing process doing a phylogenetic line
140
punctuated equilibrium
2. Changes are relatively quick and followed by long periods of little or no change (punctuated equilibrium); argue that species happens quickly due to environmental changes so some species adapt while others are destroyed (e.g. Mammals that take over habitats)
141
two theories regarding speciation/evolution
- punctuated equilibrium
| - gradualism
142
Absence of speciation:
Absence of speciation:
Species can live for millions of years with little/no change
E.g. sharks, cockroaches and horseshoe crabs
143
Critics of punctuated equilibrium:
Critics of punctuated equilibrium:
| Argue that ‘jumpy’ effect of theory count be due to incompleteness of fossil record
144
Issues with supporting either claim regarding evolution/speciation
Not enough fossils/well preserved fossils to make a proper judgement
Aspects of a species such as pigmentation, behaviour and mating calls not preserved in fossils
Just because the fossil of an extinct crocodile is similar to the modern one, doesn’t mean that they would be able to reproduce due to other factors
