19. Variation and population genetics Flashcards
What does variation mean
The differences in characteristics or phenotypes that exist
what is a Phenotype
The expression of the genotype and its interaction with the environment
What is a genotype
The genetic constitution of an organism determined by the combinatioon of alleles that an organisation inherits from its parents
What is interspecific and intraspecific variation
Interspecific variation occurs between different species.
Intraspecific variation occurs within a species.
How is variation due only to Genetic Factors
Certain characteristics of individuals in a population fall into a limited number of distinct forms, with no intermediates
This is due to genetic factors only, where only one or two genes act
what does certain characteristics within a population vary only slightly between one individual and another result in
a range of values from one extreme to the other.
Features that vary in this way are often controlled by many different genes (polygenic) and/or are usually also influenced greatly by the environment.
What does a genetic variation graph look like
A bell-shape curve
The mean medium mode are all equal
What are causes of variation
Environmental
genetic - Meiosis mutaions and random fusion of gametes
How doe the genotype and environment link to the phenotype
Genotype + Environment = Phenotype
Which method of genetic variation is the only way is asexual organisms
Mutations
How is meiosis a source of genetic variation
Meiosis is the formation of gametes
Cells are genetically different
Meiosis is a major causse of intraspecific variation
Which two ways doe smeiosis cause genetic variation in gametes
Crossing over
Independent segregration of chromosomes
How does random fertilisation of gametes causes variation
Which gamete fuses with which at fertilisation is a random process and this produces new combinations of alleles and the offspring are therefore genetically different from their parents
How does mutation cause genetic variation
causes a change in the number or sequence of bases in the DNA of an organism. This produces a change in the characteristics of the organism which can be passed on to cells produced by division of the mutant cell
How does the frequency of a mutation occur
the basic mutation rate can be increased by outside factors known as mutagenic agents or mutagens
What are mutagenic agents
· High energy ionising radiation. This can disrupt the structure of DNA
· Chemicals
What are the types of mutations
Addition/deletion
Substitution
Duplication of bases
Inversion of bases
Translocation of bases
How does an addition/deletion mutation cause genetic variation
extra base is added or removed.
This changes all the subsequent triplets after the mutation and a different amino acid sequence is made.
known as a frame shift mutation, as the ‘reading frame’ of the gene changes.
A deleted base near the end of the sequence is likely to have a smaller impact
How does a substitution mutation cause genetic variation
One amino acids in the polypeptide could change. impact will depend upon the precise role of original amino acid
The protein may be a different shape and so not function properly. (known as mis-sense mutation).
· base change could result in the formation of a stop codon that marks the end of translation.
The production of the polypeptide would be stopped prematurely. Final protein would have a significantly altered tertiary structure, and so be non-functional. ( known as a nonsense mutation).
· could cause no difference due to the degenerate nature of the genetic code ( known as a silent mutation).
What is a duplication of bases
One or more bases are repeated. This produces a frame shift to the right
What is an inversion of bases
A group of bases becomes separated from the DNA sequence and rejoin at the same position but in the inverse order
The base sequence of this portion is therefore reversed and affects the amino acid sequence coded for.
What is translocation of bases
A group of bases becomes separated from the DNA sequence on one chromosome and becomes inserted into the DNA sequence of the same or a different chromosome.
Translocations often have significant effects on gene expression leading to an abnormal phenotype.
What is a population
a group of organisms of the same species living in the same habitat or ecosystem.
What is a gene poolq
The sum total of all the alleles of all the gene loci in a population at a particular time.
What does hardyweinberg principle allow you to calculate
the proportion of each allele - the allele frequency.
What is the hardy-weinberg equation
p2 + 2pq + q2 = 1
p= dominant allele
q= recessive allele
p2 = homozygous dominant genotype
q2 = homozygous recessive genotype
2pq heterozygous genotype
What is the hardy-weinberg principle
The frequencies of the alleles of a particular gene in a population will stay constant from generation to generation.
What are the conditions in which the hardy-weinberg principle can occur
· The populations must be large
· Mating between individuals must be random.
· No mutations
· All genotypes must be equally likely to reproduce
· There must be no migration into or out of the population
What is genetic equilibium
When the hardy-weinberg principle conditions are met and the allele frequency does not change then the population
Why is the hardy-weinberg principle never valid
the ideal conditions are never met in real situations
what does the fact that a population deviates from the Hardy-Weinberg equilibrium show
that species are constantly in a state of evolutionary flux and it is possible to see to what extent natural selection and evolutionary changes are taking place by how great these deviations are.
What is genetic drift
the idea that allele frequencies can change simply due to chance
Why may genetic drift occur
beacasue of the founder effect or genetic bottlenecks:
What is the founder effect
sometimes happens that a few organisms from a population become isolated from the rest of the population,
Waht is genetic bottlenecks
A population said to go through a genetic bottleneck when it is temporarily reduced to a very small number when the majority of individuals are killed. This could be due to a chance event such as disease, volcanic eruption, flooding or hunting.
How does the founder effect and genetic bottlenecks affect the allele frequency
the new population size would be much smaller, and therefore the impact of chance on the allele frequencies would be much greater than for the original population
The new population would also show a reduction in genetic diversity due to the loss of some alleles.
