3.7 Genetics, populations, evolution and ecosystems Flashcards
Define genotype and phenotype
Genotype:
-genetic constitution of an organism
-determines the limits within characteristics may vary between individuals
Phenotype:
expression of this genetic constitution and its interaction with the environment
sme key terms
homologous pair = two copies of each chromosome, so cells have two copies of every gene
-as two copies of a gene present in an individual, possible to have different allele combinations within an individual
Genotype = alleles of a gene possessed by that individual
Homozygous = the two allele copies are identical in an individual
Heterozygous = the two allele copies are different in an individual
Genotype of an individual affects their phenotype
Phenotype = the observable characteristics of an organism
Define dominant, recessive and codominant
dominant:
-alleles that are always expressed in the phenotype, in both homozgous and heteroxygous individuals
recessive:
-only expressed in the phenotype if no dominant allele is present
-means they’re only expressed in a homozygous individual
codominant:
-both alleles are expressed in the phenotype at the same time
-seen in heterozygous individuals
-e.g. blood type
Define genes and alleles:
gene:
-sequence of DNA nucleotide bases that code for a particular protein
allele:
-different forms of a gene
difference between homozygous and heterozygous
homozygous:
-two copies of the same allele
heterozygous:
-organism has two different alleles
Define homozygous dominant and homozygous recessive
Homozygous dominant:
-organism with 2 dominant alleles
Homozygous recessive
-organism with 2 recessive alleles
Define sex-linkage
A gene whose locus is on the X chromosome
Define autosomal linkage
Genes that are located on the same chromosome, hence will be inherited together
Impacts predicted gametes
Define epistasis
When one gene modifies or masks the expression of a different gene at a different locus
Define monohybrid and dihybrid
Monohybrid: genetic inheritance cross of a characteristic determined by one gene
Dihybrid: genetic inheritance cross for a characteristic determined by two genes
Define the following:
gene pool
population
allele frequency
Gene pool: all the alleles of all the genes within a population at one time
Population: all the individuals of one species in one area at one time that can interbreed to make fertile offspring
Allele frequency: the proportion of an allele within the gene pool
Describe how a chi-squared test should be carried out
Species Exist in Populations
A species can be defined as a group of similar organisms that can reproduce to give fertile offspring
Organisms of the same species have the same number of chromosomes in their cells
Humans have 46 chromosomes
The reason that two organisms from a different species cannot produce fertile offspring is due to the fact that different species have a different diploid number of chromosomes in their cells
For example, a horse has 64 chromosomes in its cells while a donkey has 62. When the haploid gametes from a horse (32) and a donkey (31) combine, the resulting zygote has 63 chromosomes
Cells that have an odd number of chromosomes are not viable. The chromosomes can not form homologous pairs during meiosis to produce gametes
Members of a species do not live alone
Instead, they live in populations
Species can exist as one or more populations, for example:
The American black bear (Ursus americanus) is one species but has multiple populations in America and Canada
The Javan rhinoceros (Rhinoceros sondaicus) has only one population on the island of Java in Indonesia
Defining a species
The system used by biologists to organise living organisms into categories is based on dividing organisms into species
There are several factors that need to be taken into consideration when defining a species or determining whether two organisms belong to the same species
Similarities/differences in observable features (morphology)
Similarities/differences in DNA
Similarities/differences in RNA
Similarities/differences in proteins
The ability to interbreed and produce fertile offspring
The Definition of a Population
a group of organisms of the same species in a particular space at a particular time that can interbreed to produce fertile offspring
gene pools
The phenotype of an organism is dependent on its genotype and the environmental influence on the organism
Members of the same species will have the same genes, of which there may exist different alleles (alternate versions of genes)
A gene pool is the collection of genes within an interbreeding population at a particular time
As these genes can have different alleles, a gene pool can also be thought of as the sum of all the alleles of the genes of a population (of a single species) at a particular time
allele frequency
How often different alleles occur in the gene pool of a population is known as the allele frequency
The gene pool (or allele frequencies) in a species population can change over time due to processes such as natural selection
When the gene pool (or allele frequencies) within a species population changes sufficiently over time, the characteristics of the species population will also change
Over time, these changes can become so great that a new species forms
Apparatus & Techniques: Collecting Data about the Frequency of a Phenotype
The frequency of a phenotype is simply the number of individuals in a population that have a specific, observable trait (a particular phenotypic characteristic)
Many organisms have traits that show more than one phenotype (e.g. shell colour in banded snails can be pink or yellow and flower colour in pea plants can be purple or white)
Phenotype frequencies can be calculated by counting the number of times a particular phenotype appears in a population (or sample of a population) and dividing this by the total number of individuals in the population (or the sample)
Phenotype frequencies are normally given as a percentage of the total population
Phenotype frequency = (total individuals with phenotype ÷ total individuals in population) × 100
Step 1: Calculate the phenotype frequency of purple flowers
Phenotype frequency = (total individuals with phenotype ÷ total individuals in population) × 100
= (7 ÷ 9) × 100
= 0.78 × 100
= 78%
Step 2: Calculate the phenotype frequency of white flowers
Phenotype frequency = (total individuals with phenotype ÷ total individuals in population) × 100
= (2 ÷ 9) × 100
= 0.22 × 100
= 22%
Step 1: Calculate the total number of snails in the sample
= 275 + 150 + 75
= 500
Step 2: Calculate the total number of pink-shelled snails (genotypes: CᴾCᴾ and CᴾCʸ)
= 275 + 150
425
Step 3: Calculate the phenotype frequency of pink-shelled snails
Phenotype frequency = (total individuals with phenotype ÷ total individuals in population) × 100
= (425 ÷ 500) × 100
= 0.85 × 100
= 85%
Step 4: Calculate the phenotype frequency of yellow-shelled snails
Phenotype frequency = (total individuals with phenotype ÷ total individuals in population) × 100
= (75 ÷ 500) × 100
= 0.15 × 100
= 15%
Natural Selection: Hardy-Weinberg Principle
The Hardy-Weinberg principle states that if certain conditions are met then the allele frequencies of a gene within a population will not change from one generation to the next
There are seven conditions or assumptions that must be met for the Hardy-Weinberg principle to hold true
The Hardy-Weinberg equation allows for the calculation of allele and genotype frequencies within populations
It also allows for predictions to be made about how these frequencies will change in future generations
Conditions for the Hardy-Weinberg principle
-organisms are diploid
-organisms reproduce by sexual reproduction only
-there is no overlap between generations, i.e. parents do not mate with offspring
-mating is random
-population is large
-no migration, mutation, or selection (natural and artificial)
-equal allele frequencies in both sexes
-Hardy-Weinberg principle can be useful when building models and making predictions, but the assumptions listed are very rarely, if ever, all present in nature
Hardy-Weinberg equations
If the phenotype of a trait in a population is determined by a single gene with only two alleles (we will use B / b as examples throughout this section) then the population will consist of individuals with three possible genotypes:
Homozygous dominant (BB)
Heterozygous (Bb)
Homozygous recessive (bb)
When using the Hardy-Weinberg equation frequencies are represented as proportions of the population; a proportion is a number out of 1
For example if every individual in the population has the homozygous dominant genotype BB then its frequency will be 1, while if half of the population show this genotype then the frequency will be 0.5
Frequency of alleles can be represented; this is the proportion of all of the alleles in a population that are of a particular form
The letter p represents the frequency of the dominant allele (B)
The letter q represents the frequency of the recessive allele (b)
As there are only two alleles at a single gene locus for a phenotypic trait in the population:
p + q = 1
E.g. in a population of 100 individuals there would be 200 alleles because every individual has two versions of each gene
If 120 of those alleles were the dominant allele then the frequency of the dominant allele would be 120/200
It could be said that p = 120 ÷ 200 = 0.6
If p = 0.6 then q = 1 - 0.6 = 0.4
Frequency of genotypes can also be represented; this is the proportion of all of the individuals with a particular genotype
The chance of an individual being homozygous dominant is p2
The offspring would inherit dominant alleles from both parents so p x p = p2
The chance of an individual being heterozygous is 2pq
Offspring could inherit a dominant allele from the father and a recessive allele from the mother (p x q) or offspring could inherit a dominant allele from the mother and a recessive allele from the father (p x q) so 2pq
The chance of an individual being homozygous recessive is q2
The offspring would inherit recessive alleles from both parents so q x q = q2
As these are all the possible genotypes of individuals in the population the following equation can be constructed:
p2 + q2 + 2pq = 1
Ecology starts
Define ecosystem
the community and the non-living components in its environment (biotic and abiotic factors), which can vary in size
Define habitat
part of an ecosystem where particular organisms live
Define niche
an organism’s role in an ecosystem, including its position in the food web and its habitat
each species occupies its own niche, governed by adaptation to biotic and abiotic factors
Define carrying capacity
the maximum population size an ecosystem can support
Define predation
when an organism eats another
Define community
populations of different species that share a habitat
What are biotic and abiotic factors
biotic = impact of the interactions between organisms
-e.g. interspecific and intraspecific competition, predation
abiotic = non-living conditions of an ecosystem
-plants and animals are adapted to abiotic factors within their ecosystem
-e.g. temperature, oxygen, light intensity, pH
-adaptations develop through natural selection
-the less harsh the abiotic factors, the larger the range of species and the larger the population sizes
Compare interspecific and intraspecific competition
Interspecific competition:
-members of different species are in competition for the same resource that is in limited supply
-e.g. habitat, food and water
-the individual better adapted to the environment is more likely to succeed int he competition
Intraspecific competition:
-members of different species are in competition for the same resource
-e.g. mate
-individuals that are fitter will have more energy to perform a more impressive courtship ritual
-or may have fur/feathers in a better condition
predator-prey relationships
-size of the predator and prey populations always fluctuate
-there is always more prey than predators
-size of the prey population changes first
-after a lag time, the size of the predator population changes
Benefits of sampling
-more time efficient
-can be more accurate
Steps that can be taken to ensure the sample accurately represents the population
-large number of samples
-random sampling in uniform areas to eliminate bias
-line transects to measure a change over distance
sampling for mobile organisms
mark-release-recapture
sampling for non-motile / slow-moving organisms
uniform distribution
-random sampling using a quadrat
uneven distribution
-line transect and use a quadrat
What are line transects
What are the 2 factors that affect variation in phenotype
What is the primary source of variation?
What are other sources?
genetics, environment
mutation
meiosis - crossing over, independent segregation, random fertilisation of gametes
Why does meiosis result in variation?
produces new combinations of alleles
Why does random fertilisation of gametes result in variation?
produces new combinations of alleles
which gametes fuse with which is also a random process
Define polygenic
characteristic, such as height or skin color, that is influenced by two or more genes.
because multiple genes are involved, polygenic traits do not follow the patterns of Mendelian inheritance. Many polygenic traits are also influenced by the environment and are called multifactorial.
Natural selection
Define selection pressure
Give 3 examples
predation, competition, disease
What factors influence evolution by natural selection
