Variation And Evolution Flashcards
Definition of variation
The differences between organisms of the same species
How is variation generated?
- crossing over
- random distribution of chromatids
- mixing of two different parental genotypes k
Discontinuous variation
No intermediate types and characteristics are discrete
Definition of monogenic
Controlled by single genes
Definition of continuous variation
Values show a gradation from one extreme to another within a range
Selection pressure
An environmental factor that can alter the frequency of alleles in a population, when it is limiting
Gene pool
All the alleles present in a population at a given time
Allele frequency
An alleles proportion of the whole gene pool
Genetic drift
Chance variations in allele frequencies in a population
Founder effect
The loss of genetic variation in a new population established by a very small number of individuals from a larger population
3 types of natural selection
- stabilising selection
- directional selection
- disruptive selection
Types of pre zygotic isolation
- geographical isolation
- behavioural isolation
- morphological isolation
- gametic isolation
- seasonal isolation
Types of post zygotic isolation
Hybrid inviability
Hybrid sterility
Geographical isolation
- allopatric
- population split by a group physical barrier into separate demes
Behavioural isolation
- sympatric
- mating rituals and courtship displays that are recognised by other member of the species
Morphological isolation
- sympatric
- genitalia of males and females must be compatible for sperm to be transferred
Gametic isolation
- sympatric
- Gametes in open environment often meet gametes of other species
Seasonal isolation
- sympatric
- reproductive organs of different demes mature at different times of the year
Hybrid inviability
Fertilisation occurs but incompatibility between genes of parents prevents development of embryo
Hybrid sterility
Chromosomes are not sufficiently similar- unable to pair at prophase 1 of meiosis
