3.7 Genetics, Evolutions and Ecosystems Flashcards
define genotype
the genetic constitution of an organism
phenotype
the expression of this genetic constitution and its interaction with the environment
gene
a length of DNA that is a sequence of nucleotide bases which code for a particular polypeptide
allele
one of the different forms of a gene
dominant
the allele of the heterozygote that expresses itself in the phenotype
recessive
the allele of the heterozygote that is not expressed
homozygous dominant
both alleles are dominant
homozygous recessive
both alleles are recessive
codominant
neither allele is recessive, both will be expressed in the heterozygote’s phenotype
autosomes
the non-sex chromosomes, genes found here are chromosomal
asymptomatic carriers
carry one of the recessive alleles so can pass onto offspring, no symptom
monohybrid cross
shows the likelihood of different alleles of a gene being inherited by the offspring of certain parents
genetic crosses show
the genotype of the parents, the gametes’ alleles and the offspring phenotype
symbols for a codominant genetic cross
capital letters represent the genotype for the gene
superscript letters represent the alleles
dihybrid crosses show
the combination of offspring for two unlinked genes
two genes with two alleles, four different gamete combinations
one allele on each side of the cross
sex linkage, problems caused by it
The Y chromosome misses some matching genes on the X chromosome because X is longer.
There is a non homologous portion of the X chromosome.
This means recessive characteristics on the non homologous section of the X chromosome are more frequent in males (XX) because there is no chance of a dominant allele on Y to express itself.
define autosomal linkage
two or more genes are carried on the same autosome
explain autosomal linkage
Genes on the same autosome are linked because during independent segregation of meiosis 1 they stay together. Closer together, less likely to split.
define epistasis
When the allele of one gene affects or masks the expression of another in the phenotype.
If the allele is recessive, 2 copies will be needed to block its’ expression.
criteria to use chi squared
Sample size is relatively large, over 20
Data falls into discrete categories
Raw counts used, no percentages or rates
Comparing experimental results with theoretical ones
what does chi squared tell you
if observed results were statistically different to your expected results.
Must be compared to a critical value.
A means of testing where any deviation between the observed and the expected numbers in an investigation is significant or not.
null hypothesis
there is no significant difference between the two, any difference due to chance alone, so random
alternative hypothesis
there is a significant difference between the two, so linked
if chi result larger/equal to critical
reject null hypo, there is a significant link which is not due to chance
if chi result lower than critical
accept null hypo, any link is due to chance alone
degrees of freedom
number of categories minus one
hardy weinberg principle
If certain conditions are met, the allele frequencies of a gene within a population will not change from one generation to the next
necessary conditions
Diploid organism
Sexual reproduction ONLY
No overlap between generations (parents do not mate with their offspring)
Mating is random
Large population size
No migration, mutation or selection (no flow of alleles in or out and equally likely to be passed on to the next generation)
when is HW useful
when building models/making predictions of how frequencies will change in future generations
equation for allele freq
p + q = 1
equation for genotype freq
P2 + 2pq + q2 = 1
p and q represent..
p is dominant
q is recessive
Genetic variation arises from
Mutations
Meiosis (crossing over/independent assortment)
Random fertilisation of gametes
Genetic variation
a species having different alleles
Environmental variation
caused by differences in food, climate, and lifestyle
Natural selection
individuals with a fitter phenotype are more likely to survive and pass on their alleles to their offspring. The frequency of advantageous alleles increases over time and generations.
stabilising selection
Those with alleles towards the middle of the range are selected for and are more likely to survive
Tends to occur where environmental conditions remain constant for a long period of time
Allele frequency stays relatively stable unless environmental influence occurs
Reduces the range of possible offspring
directional selection
Those with a single extreme phenotype are selected for and are more likely to survive
Tends to occur if there is a change in the environment and thus selection pressures
Gradual change/fluctuation in allele frequency over time
If the environmental conditions change, the allele on one side of the curve showing the mean ‘optimum’ characteristic is favoured and selected for (selection pressures change) so allele frequency increases.
disruptive selection
Those with alleles for 2 extreme phenotypes are more likely to survive
Favours extremes at the expense of the intermediate phenotypes
Tends to occur when the environment favours more than one phenotype, the environment takes two or distinct forms e.g cold in winter, warm in summer
Directional only favours one extreme trait, disruptive favours two.
define hybrid
a sterile organisms which is the result of different species mating
define speciation
the evolution of two or more new species from new existing species
Species have the same genes but different alelles so can produce fertile offspring with each other and so are reproductively separate from other species
define adaptive radiation
the different combinations of alleles from different phenotypes are subject to selection pressures which leads to each population becoming adapted to their own environment
Causes of reproductive isolation
Geographical (physical barrier)
2. Change in:
colour/pattern
call/song
Active time of day
Reproductive times (flowering)
Reproductive organs do not match
Allopatric speciation
When populations of a species become geographically separated
Might be different environments in different locations
In order to survive, those with alleles most advantageous for survival in the environment are more likely to survive and pass on alleles to their offspring
Disadvantageous alleles therefore disappear from the population when they do not breed
Directional selection will occur and the allele frequency will change
Overtime this will cause phenotype frequency to change which will accumulate until two groups will have become separate species
sympatric speciation
When a population living in the same area become reproductively isolated
Random mutations occur within a population in the same location which prevent that individual from breeding with those without the mutation
Rarer type of speciation because it is difficult to become completely reproductively isolated without being geographically isolated as well
Carrying capacity
the maximum number of organisms that an ecosystem can support, this changes as a result of biotic and abiotic factors
intraspecific competition
When there are too many offspring for the available resources, competition occurs amongst organisms of the same species.
Plentiful resources cause an increase in population size, which causes resources to become limiting and a decrease in population again (cyclic changes.)
Deaths are not random; the individuals better suited to survival are more likely to survive than the less well adapted, so their more favourable allele combination is more likely to be passed on to the next generation. Next population has evolved a combination of alleles better adapted to survival.
interspecific competition
Organisms of different species competing for the same resources
One population has a competitive advantage over the other, so their population will increase while the other decreases.
If they cannot compete equally, the less advantaged species will likely become extinct.
define predation
the population of one species will affect the population size of the other
Effect of the predator-prey relationship on population size
Predators eat prey, reducing prey population size
Predators therefore in greater competition amongst themselves for the prey that are left
Predator population is reduced as some predators are unable to obtain enough prey to survive
Fewer predators are left so less prey eaten so more prey can survive and reproduce
Prey population increases
More prey are now available as food, so the predator population in turn increases.
instruments for sampling
Quadrats/point frames
Transects
Mark, capture, release
Nets
Pitfall traps
Pooters
size as a factor for quadrats
If a population is not evenly distributed, a large number of small quadrats will be more representative than a small number of large ones
Large or small organisms?
number of quadrats to record within the study area
The large the number the more reliable the results will be
Balance struck between time available and reliability (the number of quadrats) of the results
The random position of the quadrats within the study area
Random sampling is necessary to produce statistically different results
Random sampling
Each member of the population is equally likely to be included
An unbiased sample
Every part of each area must have an equal chance of being chosen
Can be used for differences between contrasting habitats within a habitat
method for random sampling
Lay out two long tape measures at right angles, along two sides of the study area
Obtain a series of coordinates by using random numbers taken from a table or generated by a computer
Place a quadrat at the intersection of each pair of coordinates and record the species within it
systematic sampling
Useful where a study area has an environmental gradient
Use of a transect will sample systematically along the environmental gradient.
Use point, frame or grid quadrats at regular intervals along the transect line.
running mean
Use point, frame or grid quadrats at regular intervals along the transect line.
As your data accumulates, test for the running mean and if it fluctuates within acceptable limits it is indicated that further sampling would not improve the accuracy of your data.
frequency
likelihood of a particular species occurring in a quadrat
percentage cover
estimate of the area within a quadrat that a particular species covers
abundance
the number of individuals of a species within a given area
mark release capture method
Capture a sample without doing them harm
Mark in a harmless and non obvious way
Release back into habitat
Wait a period of time and take another sample
Count all organisms, marked and unmarked
Use the equation to estimate population size
Assumptions involved
-closed population
-members randomly mix
-marks not lost
-mark doesn’t affect chances of recapture/no harm to animal
equation for mark release recapture
Total population size = number caught 1st * number caught 2nd
——————————————–
Total marked 2nd
decrease in productivity as the woodland matures
there is less light so more competition and therefore reduced photosynthesis
use your knowledge of succession to explain the increase in biomass during the first 20 years
a pioneer species causes changes in abiotic conditions which increases the number of animals
one reason for conversing woodlands
to protect niches
define species
a group of organisms that can breed together to produce fertile offspring
define uniform distribution
the same number of organisms in each region
why use percentage cover instead of frequency
too many organisms to count for frequency
describe succession in terms of types of grass populations shown on a graph
one grass is the pioneer species which changes the abiotic conditions so they become less hostile for another species to grow
the two species that cohabit represent climax community
