Evolution may lead to speciation

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  • Created by: Hindleyc
  • Created on: 31-03-19 12:14
What is variation
Differences in characteristics (phenotype) within a species and between different species
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What can it be
Physical or genetic
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how do you distinguish between the two what terms do we use
Phenotype and genotype
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What is the phenotype
Organisms Total physical appearance, constitution and behaviour.
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What does it include?
Internal characteristics eg blood group and enzyme types as well as external features eg hair colour
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What may individuals within a population of a species show
a wide range of variation in phenotype
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What is this due to
Genetic and environmental factors
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What is interspecific
Variation between different species
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What is intraspecific
Variation between members of the same species
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What are the many causes of variation
Environment, genetic (mutation and meiosis and random fertilisation of gametes)
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What is mutation
Primary source of genetic variation
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Types
Chromosomes M, Gene M (new gene)= insertion, deletion, subs
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What does sexual reproduction do
New combinations of existing genes
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What happens I it
Random assortment, crossing over, random fertilisation of gametes during sexual reproduction
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Other
Meiosis- produced further genetic variation
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What is each individual influenced by
The environment as well as their genes
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So phenotype?
genotype + environment
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What is genetic variation due to
Differences in genomes (?genetic makeup) of individuals
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What can it be due to
Mutation (changes in nucleotide seq of a gene), random fertilisation , independent assortment, crossing over
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What is random fertilisation
2 gametes fuse to form a zygote
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and
Each gamete has a unique combination of genes, any of the numerous male gametes can fertilise any of the numerous female gametes therefore every zygote is unique
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What is independent assortment
Meiosis when chromosomes line up at equator- each bivalent made up of 2 homologous chromosomes
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Where did these orignially come from
2 different parents (often called maternal and paternal chromosomes)
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and what can they do
Line up in any orientation on equator, the maternal and paternal versions of the diff chromosomes can be mixed up in the final gametes
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what is Crossing over
in Meiosis when bivalents first form while 2 homologous chromosomes are joined in a bivalent, bits of 1 chromosome are swapped (crossed over) with the corresponding bits of the other chromosome
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What does crossing over mean
That maternal and paternal alleles can be mixed even though they are on the same chromosome
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How can variation in a population be studied
By measuring the characteristics in a large number of different individuals and plotting a frequency histogram
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How is it set out
Values of characteristic on X and no. of individuals showing that characteristic on Y
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What are the 2 major types of variation
Discontinuous and continuous
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What is discontinuous
Distinct categories (discrete) where individuals can be placed
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What does it tend to be
Qualitative
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What is there no overlap between
categories
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What is it controlled by
Few genes (1 or small number)
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What is it unaffected by
environment
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What does a frequency histogram have
Separate bars
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What is it rare in? more common in?
Humans and other animals, plants
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EG
Blood group= clear cut result, ear lobes detached, flower and seed colour
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What is continuous
No distinct categories into which individuals can be placed
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What does it tend to be
Quantitative - overlap between categories
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What is it controlled by
Lots of genes (polygenic)
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What is it strongly influenced by?
Environment
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what does it have
Range of values and a smooth curve (nd)
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What is it v common in
humans and other animals eg height
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What do you sometimes see
Effect of both variations
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eg
Height bimodal (2 peaks/) because 2 sexes (a discontinuous characteristic) each have their own normal distribution of height - a continuous characteristic
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What is natural selection
Predation, disease and competition for the means of survival result in differential survival and reproduction eg natural selection
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What is Darwins theory of evolution by natural selection based on
4 observations- individuals within a species differ from each other - there is variation, offspring resemble their parents- genes are inherited, far more offspring are generally produced than survive to maturity-
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what do most organisms die young from
predation, disease and competition, and populations are usually fairly constant in size
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What did he realise
Organisms that die young weren't random but selected by their characteristics
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What do individuals that are better adapted to their environment do
Compete better than the others, survive longer and reproduce more so passing on more of their successful genes to the next generation
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What do Differences b/w reproductive success of individuals affect
allele freq in populations
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How does process work
All organisms produce more offspring than can be supported by the supply of food, light, space etc
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despite this overproduction of offspring what do most populations remain
relatively constant in size which means there is competition between members of a species to be the one that survives
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What will there be within any population of a species
a gene pool containing a wide variety of alleles
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What will some individuals posses
a combination of alleles that make them better able (fitter) to survive in their competition than others
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so what are these individuals more likely to obtain
the available resources and so grow more rapidly and live longer so as a result will have a better chance of successfully breeding and producing more offspring
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What will only those individuals that successfully reproduce do
Pass on their alleles to the next generation
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therefore what is more likely to be passed on to the next generation
alleles that gave parents an advantage in competition for survival
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As the new individuals have advantageous alleles what are they in turn more likely to do
survive and so reproduce successfully and over many gen number of individuals with advantageous allele will increase at expense of individuals with less advantageous alleles
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over time what will happen
freq of advantageous alleles in the population will increase while that of non advantageous ones will decrease
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So those organisms with phenotypes providing selective advantages are more likely to
produce offspring and pass on their favourable alleles to the next gen - changes allele freq within a gene pool
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if more likely to pass on
allele freq will increase in gene pool
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What does an advantageous allele depend on
environmental conditions at any 1 time
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What is selection
Process by which organisms that are better adapted to their environment survive and breed while those that are less well adapted fail to do so
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How can changes be recorded
as changing histogram of a particular phenotype (due to changes in underlying alleles)
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What do populations do over time? why
change as their environment changes
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what do different environmental conditions favour
different characteristics
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3 types of selection
Stabilising, directional, diverging (disruptive)
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What is stabilising
Intermediate phenotype selected over extremes, occurs when E doesn't change much, extreme less likely to pass on alleles
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what is favoured
Phenotype around the mean selected for
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What is directional selection
Phenotype at 1 extreme selected for, extreme favoured over other extreme so when environment changes more likely to survive and breed therefore contribute to offspring in next generation - mean moves
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why Is it common
as most environments change
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What does the environment contain
biotic and abiotic so organisms evolve in response to each other
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What is disruptive/ diverging
Both extremes are favoured over intermediate types
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What does type of selection depend on
Which phenotype are selected by the environment
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What is speciation
Origon of a new species
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define
Evolution of new species from existing species
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What do species belong to
same gene pool
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What doesn't natural selection have to cause, why
a directional change if E doesn't change because no pressure for well adapted species to change
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How does speciation work
1 existing species splits into 2 reproductively isolated populations that go their separate ways
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What may the environmental conditions /factors that each group encounters
differ
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What will selection do
affect the 2 populations in different ways and so type and frequency of alleles in each will change
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What will each population do
Evolve along along separate lines
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Other cards in this set

Card 2

Front

What can it be

Back

Physical or genetic

Card 3

Front

how do you distinguish between the two what terms do we use

Back

Preview of the front of card 3

Card 4

Front

What is the phenotype

Back

Preview of the front of card 4

Card 5

Front

What does it include?

Back

Preview of the front of card 5
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