Genetics, populations, evolution, and ecosystems Flashcards
Allele
A version of a gene.
Dominant
Describes an allele that is always expressed. Represented by a capital letter
Diploid
Describes a cell with a nucleus containing two sets of chromosomes.
Gene
A length of DNA on a chromosome that codes for the production of one or more polypeptide chains and functional RNA.
Genotype
An organism’s genetic composition. Describes all alleles.
Heterozygous
When someone has two different alleles of a gene e.g. Ff.
Homozygous
When someone has two identical alleles of a gene e.g. ff.
Locus
The position of a gene on a chromosome.
Phenotype
An organism’s observable characteristics. Due to interactions of the genotype and the environment.
Recessive
An allele that is only expressed in the absence of a dominant allele.
Codominant
When both alleles for a gene in a heterozygous organism equally contribute to the phenotype.
Dihybrid inheritance
The inheritance of two different genes, that determine two
phenotypes, on two different chromosomes.
Monohybrid inheritance
When a phenotype or trait is controlled by a single gene.
Example of codominance
shown in human ABO blood groups. There are three
alleles that are associated with the immunoglobulin gene (gene I). These lead to different
antigens on their surface, these are:
1. Allele IA - leads to the production of antigen A
2. Allele IB - leads to the production of antigen B
3. Allele Io - leads to the production of neither antigen A or B
Sex linkage
the expression of an allele dependent on the gender of the individual as the gene is located on a sex chromosome.
How many pairs of autosomal chromosomes do humans have?
22 pairs
Example of sex linkage diseases
Haemophilia which is a disease in which the blood clots slowly and there may be slow and persistent internal bleeding, especially around
the joints. It is caused by a change to the DNA sequence resulting in a faulty protein being created.
Why is the the haemophilia only inherited by the mother?
As a male can only obtain the Y chromosome
from his father, it means that the X chromosome
must come from his mother.
As this disease is not found on the Y chromosome it means that this disease is always inherited from the mother in
males. If the mother doesn’t suffer from the disease but is heterozygous with the alleles then she is a carrier.
Autosomal linkage
Two or more genes are positioned on the same autosome. They
are unlikely to be separated by crossing over during meiosis so are often inherited together
Epistasis
Describes a relationship between genes where the allele of one gene affects the expression of a different gene.
Recessive epistasis
occurs when the presence of a recessive allele prevents the expression of another allele at a second locus.
Dominant epistasis
Is when a dominant allele at one locus completely masks the alleles at a second locus.
What is the ratio of Recessive epistasis?
9:3:4.
What ratio does Dominant epistasis gives a ratio of?
12:3:1
Chi-squared
is a statistical test which can be used to establish whether the difference
between observed and expected results is small enough to occur purely due to chance. It can be used to test the null hypothesis.
Criteria of a null hypothesis
- The sample size must be sufficiently large enough, that is over 20.
- Used only for data that falls into discrete categories.
- Only raw counts and not percentages, rates, etc can be used
Formula for chi-squared
x squared = sum of all (observed - expected)2 / expected
What is the critical value
p=0.05
Where the value obtained is equal to or greater than the critical value, the null hypothesis is accepted as the difference due to chance is not significant. To read off the value though the degrees of freedom need to be known. These are simply the number of categories minus one.
What happens if the value is less then the critical value?
The null hypothesis is rejected
What happens if the value is equal or greater than the critical value
The null hypotheis is accepted
Population
Is a group of organisms of the same species occupying a particular space at a particular time that can potentially interbreed
Gene pool
The total number of alleles that are present in a population
allelic frequency
Expresses as a decimal or percentage the proportion of a certain allele in a gene pool.
Hardy-Weinberg Equation
Can be used to estimate the frequency of alleles in a population and to see whether a change in allele frequency is occurring in a population over
time.
What are the 5 conditons for the proportion of dominant and recessive alleles of any gene is a population remains the same from one generation to the next?
- No mutations occur to create new alleles.
- There is no movement of alleles into or
out of the population by migration. - Population is large.
- No selection, so every allele has an equal chance of being passed to the
next generation. - Mating is random.
What is the The formulae for Hardy-Weinberge?
p + q = 1.0 AND p² + 2pq + q² = 1
What does the P stand for in the p+q=1.0 formulae
p = the frequency of the dominant allele (represented by A)
What does the q stand for in the p+q=1.0 formulae?
q = the frequency of the recessive allele (represented by a)
What does p² stand for in the 2pq + q² = 1 formulae?
q2 = frequency of aa (homozygous recessive)
What does 2pq stand for in 2pq + q² = 1 formulae?
Frequency of Aa (heterozygous)
There are variations in the alleles of genes for members of the same species due to a number of factors such as:
- Random fertilisation - the gametes that are carrying different alleles will join together
randomly. - Meiosis - meiosis is the nuclear division that creates gametes and means that the alleles will
be assorted in the gametes at random. - Mutation - the mutation of an allele can go on to lead to the creation of another new allele
which can then be passed to the next generation
Niche
Describes how an organism ‘fits’ into an ecosystem and its role in that environment
Intraspecific competition
A type of competition that takes place between members of the
same species.
Interspecific competition
A type of competition that takes place between members of
different species.
Selection
is the process by which individuals that are better adapted to their environment are more likely to survive and breed.
Directional Selection
occurs when the environmental conditions change and the phenotypes best suited to the new conditions are more likely to survive
Stabilising Selection
In stabilising selection the phenotypes with successful characteristics
are preserved and those of greater diversity are reduced.
Disruptive Selection
A type of selection that favours individuals with extreme phenotypes
and selects against those with phenotypes close to the mean
Speciation
the process by which new species arise after a population becomes separated and cannot interbreed.
Allopatric speciation
A form of speciation that occurs when two populations become
geographically isolated. Results in the gene flow being reduced
sympatric speciation
A form of speciation that occurs when two populations within the
same area become reproductively isolated.
Ecosystem
The community of organisms (biotic) and non-living (abiotic) components of an area and their interactions. It is a dynamic system.
The abiotic factors that affect population growth are:
- Temperature
- Light
- pH
- Water and humidity
Predator
An organism that eats other organisms.
Prey
An organism that is eaten by predators.
Predatorprey relationship and occurs as follows:
- When the prey is eaten by the predator the population of the prey falls.
- This results in the predator population growing, however means that more prey is consumed.
- Therefore the population of prey reduces and there is increased competition for the the prey
between the predators. - The lack of food for the predators means that the population falls meaning that less prey is
eaten. - This allows the population of the prey to recover and therefore the cycle occurs over in a
oscillating manner.
The abundance of different species
can be measured in two main ways these are:
Percentage cover
Frequency
Percentage cover
suitable for plants or algae whose individuals numbers are difficult to
count.
Frequency
expressed as a decimal or percentage, and is the number of times an organism
appears in the sampling area
mark-release-recapture
- Known number of species is captured and marked in a way that doesn’t reduce their chance of survival.
- These marked organisms are then released again into the same area they were caught.
- After a suitable length of time another known number of organisms are captured, with the number of these that are marked being recored
Population can be estimated using the following equation:
Estimated population size = Total number of individuals in the first sample X Total number of individuals in the second sample/ Number of marked individuals recaptured
Population can be estimated using the following equation:
Estimated population size = Total number of individuals in the first sample X Total number of individuals in the second sample/ Number of marked individuals recaptured
Succession
Describes changes in the community of organisms occupying a certain area over time.
Primary succession
occurs when area previously devoid of life is colonised by communities of organisms. E.g after the eruption of a volcano which lead
to formation of a rock surface.
Secondary succession
occurs in a previously colonised area in which an existing community has
been cleared. This type of succession can occur after events such as forest fires.
Conservation
The human management of the Earth’s resources and typically involves the managing of succession. E.g the controlled burning of land is done in order to stop the formation of a climax community.
