Variation and selection Flashcards
what is variation
differences between individuals of the same species
what is continuous variation
results in a range of phenotypes between two extremes. Examples body length and body mass
what is discontinuous variation
results in a limited number of phenotypes with no intermediates. Example ABO blood groups, seed shape in peas and seed colour in peas
what is discontinuous and continuous variation caused by
discontinuous variation is usually caused by genes only and continuous variation is caused by both genes and the environment
describe mutation
genetic change. Is the way in which new alleles are formed
what does ionising radiation and some chemicals cause
they increase the rate of mutation
what is gene mutation
a random change in the base sequence of DNA
what are sources of genetic variation
genetic variation can be caused by mutation ( which can create entirely new alleles in a population), random mating, random fertilization and recombination between homologous chromosomes during meiosis ( which reshuffles alleles within and organism offspring)
what is an adaptive feature
an inherited feature that helps an organism to survive and reproduce in its environment
explain adaptive features of hydrophytes
live in wet conditions- 1. have large air spaces to keep them close to the surface to get more light
2. small roots so they can also extract nutrients from the surrounding water
3. stomata found in the upper epidermis in order to exchange gases much more easily with air
adaptive features of xerophytes
live in dry conditions- 1. thick waxy cuticle to prevent water loss as it acts as a barrier to evaporation and the shiny surface
2. thickened leaves contain cells that store water
3. extensive shallow roots allow for quick absorption of large quantities of water
4. sunken stomata trap moist air and lengthens the diffusion pathway and reduces evaporation rate
5. small leaves reduce surface area therefore reduces the evaporating surface
describe natural selection
natural selection shows a range of variation. When organisms reproduce, they produce more offspring than the environment is able to support.
This leads to: -competition for food
- competition for survival as the individuals with characteristics most suited to the environment have a higher rate of survival and more chance to reproduce therefore these alleles are passed to their offspring at a higher rate
describe selective breeding
selective breeding is done by a selection by human of individuals with desirable features. They cross these individuals to produce the next generation, until the ‘new breed’ will reliably show these characteristics in all offspring.
How does artificial selection take place
- individuals with the characteristics you want are bred together
- offspring that show the desired characteristics are selected and bred together
- this process is repeated for many successive generations before you can have a ‘new breed’
what is adaptation
the process, resulting from natural selection, by which populations become more suited to their environment over many generations
