Variation Flashcards
Define discontinuous variation
Qualitative differences falling into discrete categories. No intermediate categories. Usually affected by one or two genes.
Give an example of discontinuous variation
E.g blood type
Define continuous variation
Quantitative differences between phenotypes. Wide range of variation in the population. Usually affected by both genetics and environment.
Give an example for continuous variation
e.g. height
What is a cause of discontinuous variation
Usually different alleles at a single gene locus have a large effect on the phenotype
The environment has a limited effect on the phenotype
What is a cause of continuous variation
Many different alleles at a single gene locus having small effects
Different gene loci have the same, often additive effect on the phenotype
A large number of different gene loci (polygenese) may have a combined effect on the trait
The environment has a large effect on the phenotypic trait
Define gene pool
The sum total of all the different alleles in a population
Define allele frequency
How often an allele occurs in a population and is expressed as a decimal. The frequency can change over time due to evolution.
What is the hardy weinburg principle
A method to predict the frequency of alleles in a population wont change from one generation to the next
What are the hardy weinburg principle assumptions
The population is large
Mating is random
No selective advantage to any particular phenotype
No mutations, migrations or genetic drift
What is the Hard weinburg calculation
P= frequency of dominant allele A Q= Frequency of recessive allele a
Frequency of homozygous dominants: P^2
Frequency of homozygous recessive: Q^2
Frequency of heterzygous: 2PQ
Allele frequencies: P+Q =1
Genotype frequencies: P^2 + 2PQ + Q^2 =1
Describe genetic drift
Due to chance. There will be variation in the population but by chance one particular allele may be passed on rather than another. If this process is repeated over many generations then the allele frequency will decrease.
Describe a genetic bottleneck
When an extreme event occurs causing a big reduction in the size of a population. This means that genetic drift has a greater effect.
What is natural selection
Genetic variation means that some organisms will have a better chance of survival than others. These organisms are better adapted, more likely to survive, breed and pass on their alleles to the next generation. This increases the chance of the advantageous alleles being passed on to the next generation and the allele frequency increasing.
Define selection pressure
Environmental factor that confers greater chances of surviving and reproducing on some members of the population than others.
What is the biological species concept
A group of similar organisms capable of interbreeding, producing fertile offspring and that are reproductively isolated from other such groups.
What is the phylogenetic species concept
A group of organisms that show a close similarity in morphological, physiological, embryonic, ecological and behavioural characteristics forming the basis of classification showing an evolutionary lineage.
Define clade
Group consisting of a single common ancestor and all the descendants of the ancestor and from a monophyletic group
Define speciation
A large population of organisms may be split into sub groups by various isolating mechanisms the sub group then evolves through natural selection and are unable to interbreed to produce fertile offspring.
How does geographical isolation occur
Organisms are separated by a physical barrier such as a river or mountain. The sub group becomes genetically isolated and experiences different selection pressures, different alleles may become favourable and the population will evolve through natural selection.
What does geographical isolation lead to
Allopatric speciation
What does reproductive isolation lead to
Sympatric speciation
How does reproductive isolation occur
Differences in courtship, mechanical problems, gamete incompatibility, hybrid sterility. The sub group becomes genetically isolated and experiences different selection pressures, different alleles may become favourable and the population will evolve through natural selection.
What are ecological barriers
When two species live in the same area at the same time but rarely meet so do not interbreed.
What are temporal barriers
When two species live in the same place but do not interbreed because they are not active ta the same time of the day or do not reproduce at the same time of the year
What is selective breeding
Breeder chooses an individual with desirable phenotypes for breeding and prevents those with undesirable features from breeding. The process is repeated over many generations this then increases the allele frequency for the desirable trait in the population.
Describe the selective breeding process in cows
Performance testing: Each cows milk yield is measured and recorded.
Progeny testing: The offspring of bulls are tested to find which have produced daughters with high milk yield, aiding in determing the genotype of the bull.
A few good bulls are required to provide semen to artificially inseminate many cows
Cows with high milk production are given hormones to super ovulate and the eggs are flushed out
Give a disadvantage of using artificial selection in dairy cows
Udders can become inflamed leading to mastitis
Diary cows can have strain on their legs due to increase size of their udders.
Describe artificial selection using bread wheat
Has lead to increase yield, higher protein content, shorter stalks to prevent bending in the rain and wind. Disease resistance.
Give a disadvantage to using artificial selection in bread wheat
Reduce genetic diversity within the species, making the species more vulnerable to coping with changing selection pressures.
