3.7 genetics, populations, evolution and ecosystems Flashcards
phenotype
The observable or biochemical characteristics of an organism.
The result of the interaction between the expression of the genotype and the environment.
The environment can alter an organism’s phenotype
genotype
Is the genetic composition of an organism.
Describes all of the alleles that an organism has.
Determines the limits within which the characteristics of an individual may vary.
allele
Is 1 of the different forms of a gene.
Only 1 allele of a gene can occur at the locus of any 1 chromosome.
In diploid organisms the chromosomes occur in pairs called homologous chromosomes.
Are therefore 2 loci that each carry 1 allele of a gene. If the allele for each of the chromosomes is the same, it is said to be homozygous. If its different, its said to be heterozygous.
genes
A length of DNA, that is a sequence of nucleotide bases, that normally code for a particular phenotype.
A gene does this by coding for a particular polypeptide.
This polypeptide may be an enzyme that is needed in the biochemical pathway that leads to the production of the characteristics.
monohybrid cross
Pure breeding green pea pod plant crossed with a pure breeding yellow plant. (homozygous). The result was that all of the offspring were green pea pods, so green must be dominant.
Gene for pea pod colour- feature ( use a particular letter to represent it, making sure it has different upper and lower case if possible), so there is 2 alleles.
Let G represent the dominant allele green.
Let g represent the recessive gene yellow.
(homozygous)
Parents- phenotype pure bred green × pure
bred yellow
Genotype GG → gg
Gamete G G g g
F1- 1st filial gen Gg Gg Gg Gg
Offspring of X
F1 phenotype green green green green
Expected Ratio All green
autosomal linkage
Any 2 genes that occur on the same chromosome are linked.
2 or more genes are carried on the same autosome is autosomal linkage
Are physically joined together and cannot move.
multiple alleles
A gene may have more than 2 alleles and so has multiple alleles.
E.g.. ABO. There are 3 alleles associated with the gene I ( immunoglobulin gene) :
IA- leads to the production of antigen A
IB- leads to the production of antigen B
IO- leads to the production of antigen O.
Despite there being 3 alleles, only 2 can be present in an individual at any one time.
multiple alleles
A gene may have more than 2 alleles and so has multiple alleles.
E.g.. ABO. There are 3 alleles associated with the gene I ( immunoglobulin gene) :
IA- leads to the production of antigen A
IB- leads to the production of antigen B
IO- leads to the production of antigen O.
Despite there being 3 alleles, only 2 can be present in an individual at any one time.
back cross
Allows you to determine the genotype of an ‘unknown’ phenotype.
Use it against a homozygous recessive
sex linkage
As females have 2 X chromosomes, all gametes are the same n that they contain a single x chromosome.
Males have 1 X, 1 Y chromosome they produce 2 different gametes
co-dominance
Occurs where instead of 1 allele being dominant and the other recessive, both alleles are equally dominant
dihybrid cross
How two characters, determined by two different genes located on different chromosomes are inherited. Always 9:3:3:1 ratio
chi-squared test
Used to test null hypothesis.
A means of testing whether any deviation between the observed and expected numbers in significant or not.
The value obtained is the read off a chi-squared distribution table to determine whether deviation from expected results is significant or not.
what is the criteria for the chi-squared test
Can only be used if certain criteria is met:
1- sample size is relatively large. At least 20.
2- data must fall in discreet categories.
3- only raw counts, no %, rates etc. can be used.
4- used to compare experimental results to theoretical results.
how do you tell if deviation is significant
To do so you need to know the degree of freedom.
The critical value is p=0.05.
If the deviation is equal or greater than 0.05, the deviation is not significant and null hypothesis is accepted.
If deviation is less than 0.05, the deviation is significant and null hypothesis is not accepted.
chi-squared equation
X^2 = (O-E)^2 / E
hardy-weinberg
Provides a mathematical equation that can be used to calculated the frequencies of the alleles of a particular gene in a population.
Makes the assumption that the proportion of dominant or recessive alleles of any gene in a population remains the same from 1 generation to the next
hardy conditions
this can be the case provided that 5 conditions are met:
1- no mutations arise
2- the population is isolated. Where no alleles flow into or out of the population
3- there is no selection, where alleles are all equally likely to be passed to the next generation.
4- the population is large
5- mating within the population is random.
hardy-weinberg equation
p^2 + 2pq + q^2 = 1
p + q = 1
populations
A population is a group of organism of the same species that occupies a particular space at a particular time and that can potentially interbreed.
All the alleles of all the genes of all the individuals in a population at a given time are known as the gene pool (deme). The number of times an allele occurs within the gene pool is referred to as allelic frequency.
variation due to genetic factors
Within a population, all members have the same genes. Genetic differences, however, occur as members of this population will have different alleles of these genes.
These differences not only occur in living individuals but also change from generation to generation.
Genetic variation arises as a result of:
Mutations- these sudden changes to genes and chromosomes may, or may not be passed on to the next generation.
Meiosis- this special form of nuclear division produces new combinations of alleles before they are passed on into the gametes
Random fertilisation- in sexual reproduction this produces new combinations of alleles and the offspring are therefore different from the parents. Which gametes fuses with which at fertilisation is a random process further adding to variety of offspring.
variation due to environmental factors
Environment exerts an influence on all organisms. These influence affect the way the organisms genes are expressed.
Genes set limits, but its largely the environment that determines where, within those limits, an organism lies.
natural selection
The individuals in a population that is best suited to prevailing conditions ( e.g. Better able to hide/escape predators, better able to obtain light/catch prey) will be more likely to survive than those less well adapted. Will be more likely to breed and so pass on their more favourable allele combinations to the next generation, which will therefore have a different allelic frequency from the previous one.
Populations showing little individual genetic variation are often more vulnerable to new diseases and climate changes.
A larger population, with more genetically varied individuals, the greater the chance 1 or more individuals will have the combination of alleles that lead to a phenotype which is advantageous in the struggle for survival.
intraspecific vs interspecific competition
Intraspecific- Competition from individuals from the same species.
Interspecific- competition between different species
stabilising selection
Tends to eliminate the extremes of the phenotype range within a population and with it the capacity for evolutionary change.
Tends to occur where the environment conditions are constant over long periods of time.
directional selection
Results in 1 extreme of a range of variation being selected against in favour of the other extreme or even the average
disruptive selection
Favours extreme phenotypes at the expense of the intermediate phenotypes.
Most important in bringing about evolutionary change. Occurs when an environmental factor takes 2 or more distinct form.
allelic frequency and how variation effects it
The number of times an allele occurs within a gene pool is referred to as the allelic frequency.
Is affected by selection and selection is due to environmental factors. So environmental changes therefore affect the probability of an allele being passed on in a population and hence the number of times it occurs in the gene pool. Only affect the frequency of a mutant allele that is already present in the gene pool
speciation
Is the evolution of new species from existing ones.
Species- group of individuals that have a common ancestry and so share the same genes but different alleles and are capable of breeding to produce fertile offspring
forming new species
The most important way a new species if formed is through reproductive separation followed by a genetic change due to natural selection.
The different phenotypes each combination of alleles produce will be subject to selection pressures that will lead to each population becoming adapted to its local environment. ( known as adaptive radiation). It results in changes to allele frequencies.
Genetic drift is something that can take place in small populations. Is because the relatively few members of a small population posses a smaller variety of alleles than the members of a large population. So their genetic diversity is less.
Any mutation to 1 of these alleles that is selectively favoured will also more quickly affect the whole population because its frequency will be high. The effects of genetic drift will be higher and the population will change relatively rapidly, making it more likely to develop into a separate species.
allopatric speciation
Allopatric means different countries and describes the form of separation where 2 populations become geographically separated.
Geographical separation may be the result of any physical barrier between 2 populations which prevents them from interbreeding.
Barriers include- oceans, rivers, mountain ranges and deserts.
Barriers may be a problem for 1 species but wont be for another
sympatric speciation
Sympatric means same country and describes the form of speciation that results within a population in the same area leading to them becoming reproductively separated
geographical variation
Populations are isolated by physical barriers such as oceans
ecological variation
Populations inhabit different habitats within the same area and so individuals rarely meet
temporal variation
Breeding season don’t coincide and so don’t interbreed
behavioural variation
Mating is often preceded by courtship which is stimulated by different characteristics. Any mutation may cause a change in those and may prevent mating
mechanical variation
Anatomical differences may prevent mating occurring
gametic variation
Gametes may be prevented from meeting due to genetic or biochemical incompatibility
hybrid sterility variation
Hybrids formed from the fusion of gametes from different species are often sterile because they cannot provide viable offspring.
ecosystems
Are dynamic (moving) systems made up of a community and all the non-living factors of it’s environment.
Can range in size from very small to very large.
Are 2 major processes within to consider:
Flow of energy through the system
Cycling of elements within the system
Within each ecosystem, there is a number of species. Each species is made up of a group of individuals that make up a population.
populations
A group of individuals of 1 species that occupy the same habitat at the same time and are potentially able to interbreed. An ecosystem supports a certain type of population of a species called the carrying capacity.
The size of a population can vary as a result of:
Effect of abiotic factors
Interactions between organisms.
Populations of different species forms a community
communities
Is defined as all the populations of different species living and interacting in a particular place at the same time.
habitats
Is the place where an organism normally lives and is characterised by physical conditions and other types if organisms present.
Within an ecosystem there are many habitats
Within each habitat, there is smaller units, each with their own microclimate. These are called microhabitats.
plotting population growths
Where a population grows in size slowly over a period of time it is possible to plot a graph of numbers in a population against time.
Where the population grows rapidly over a short period of time, this may not be possible.
If we try to plot a graph of numbers against time using a time scale that allows differentiation of each point, the curve runs off the graph. So you use a logarithmic scale to represent the number.
population size
No population continues to grow indefinitely because certain factors limit growth
E.g. availability of food, light, water, oxygen and shelter, and the accommodation of toxic waste, disease and predators.
Each population has a certain size, the carrying capacity, that can be sustained over a relatively long period and is determined by limiting factors.
ecological niche
A niche describes how an organism fits into the environment. It refers to where an organism lives and what it does there. Includes all biotic and abiotic conditions to which an organism is adapted to in order to survive, reproduce and maintain a viable population.
Some species may appear to be similar but their nesting habitats or other aspects of behaviour will be different , or they may show different levels of tolerance to environmental factors such as pollutant or oxygen shortages.
No 2 species occupy the same niche. Is known as the competitive exclusion principle
temperature and ecosystems
each species has an optimum temperature at which is best able to survive. The further away from it, the fewer individuals are able to survive.
In plants and cold-blooded animals, the lower the temperature. The slower their enzymes work and so the metabolic rate is reduced. Populations therefore have a low carrying capacity. At temperatures above, enzymes don’t work as efficiently as they gradually undergo denaturation.
Warm-blooded animals can maintain a relatively constant temperature regardless of external. The further away the temperature gets, the more energy is expended in trying to maintain the normal body temperature, leaving little energy for individual growth and so mature more slowly.
light and ecosystems
As the ultimate energy source for most ecosystems, light is a basic necessity of life. Rate of photosynthesis increases as light intensity increases. Greater the rate of photosynthesis, the faster plants grow and the more spores or seeds they produce. ( increases carrying capacity).
pH and ecosystems
Affects the action of enzymes. Each enzyme has an optimum pH at which is operates at the most effectively. A population is larger where the appropriate pH exists, and smaller ( or non-existent) when the pH is not the optimum
water and humidity and ecosystems
Where water is scarce, populations are small and consist only of species that are well adapted to living in dry conditions. Humidity affects transpiration rates in plants and the evaporation of water from animals. In dry conditions, the populations adapted to tolerate low humidity will be larger than those who haven’t.
what is the criteria for the chi-squared test
Can only be used if certain criteria is met:
1- sample size is relatively large. At least 20.
2- data must fall in discreet categories.
3- only raw counts, no %, rates etc. can be used.
4- used to compare experimental results to theoretical results.
