Chapter 17: Selection And Evolution Flashcards
Causes of genetic variation:
- independent assortment of chromosomes
- crossing over
- random mating
- random fertilisation of gametes
- mutation
Discontinuous variation definition
Qualitative differences that fall into clearly distinguishable categories
Discontinuous variation example
Blood group
Continuous variation definition
Shows a range of phenotype
Continuous variation example
Height
Biotic factors definition
Caused by another organism (e.g. Predators, competition for food)
Abiotic factors definition
Natural selection caused by non-living organisms (e.g. Water supply)
Natural selection definition
The effect of selection pressures on the frequency of alleles in a population
Directional selection
A new environmental factor or a new allele appears, which changes allele frequency
Disruptive selection
Occurs when conditions favour both extremes of a population
Genetic drift definition
A change in allele frequency that occurs by chance, because only some of the the organisms of each generation reproduce
Founder effect
Further genetic drift in the small population that alters the allele frequencies, and leads to the evolution of the offspring species in a different direction to the parent population
What is the Hardy-Weinberg principle used for?
Allows proportions of genotypes in a large, randomly mating population to be calculated
What does ‘frequency’ refer to in the Hardy-Weinberg principle?
The genotype’s proportion of the whole population
In which situations does the Hardy-Weinberg principle NOT apply?
- when there are significant selective pressures against one genotype
- when individuals migrate, carrying alleles into/out of the population
- where there is non-random mating
