Variation and selection Details Flashcards
Examples of continuous variation
-Body length
-Body mass
Examples of discontinuous variation
-ABO blood groups
-Eye colour
-Dominant hand
Cause of discontinuous variation
Genes only
Cause of continuous variation
Genes and the environment
Mutation is the way in which…
new alleles are formed
Factors which increase the rate of mutation
-Ionising radiation
-Certain chemicals(eg.carcinogens)
Sources of genetic variation in populations
-Mutation
-Meiosis
-Random mating
-Random fertilisation
Adaptive features of xerophytes
-Thick cuticle(to minimize transpiration)
-Small leaves(to reduce surface area for transpiration)
-Less stomata(to reduce surface area for transpiration)
-Sunken stomata(to maintain humidity around stomata, hence reducing diffusion of water out of the plant)
-Rolled leaves to maintain humidity around stomata
-Extensive roots to maximize water uptake
Adaptive features of hydrophytes
-Wide flat leaves(to increase surface area for floatation/be exposed to as much light as possible)
-Reduced plant structure(less need for structural support)
-Thin waxy cuticle(water preservation not as important)
-Small roots(water can be taken directly from the leaf and stem)
-Stomata are open on the upper side of the leaf(to maximize gas exchange)
-Large air spaces in leaves(to keep them close to surface of water where there is more light for photosynthesis)
Process of natural selection
-Genetic variation within populations
-Production of many offspring
-Struggle for survival(eg. competition for resources)
-Greater chance of reproduction for individuals more adapted to the environment
-These individuals pass on their alleles to the next generation
Process of selective breeding
-Selection by humans of individuals with desirable features
-Crossing these individuals to produce the next generation
-Selection of offspring showing the desirable features
Benefit of selective breeding
Over many generations it can improve the quality of crop plants and domesticated animals
