Chapter 18 - Variation and selection Flashcards
What is variation?
Variation is differences between individuals of the same species.
What is continuous variation?
Continuous variation results in a range of phenotypes between two extremes. E.g. body length and body mass.
What is discontinuous variation?
Discontinuous variation results in a limited number of phenotypes with no intermediates. E.g. blood groups, seed shapes and seed colours in peas.
How is variation caused?
Discontinuous variation is usually caused by genes whereas continuous variation is usually caused by both genes and the environment.
What are mutations?
Mutations are genetic changes. (they are ways in which new alleles are formed)
What are gene mutations?
Gene mutations are random changes in the base sequence of DNA.
How can you increase the rate of mutation?
Ionising radiation and some chemicals such as ultraviolet can increase the rate of mutation.
What causes genetic variation in populations?
Mutation, meiosis, random mating and random fertilisation are all sources of genetic variation in populations.
What are adaptive features?
Adaptive features are inherited features that helps and organisms to survive and reproduced in its environment.
What are hydrophytes and how are they adapted to live in extremely wet conditions?
Hydrophytes are plants adapted to live in extremely wet conditions. Common adaptations include large air spaces in their leaves for floatation and to keep the leaves close to the surface of the water where there is more light for photosynthesis. Small roots as they can also extract nutrients from the surrounding water through their tissues. Stomata is usually open all the time and mainly found on the upper epidermis of the lead where they can exchange gases much more easily with the air.
What are xerophytes and how are they adapted to live in extremely dry conditions?
Xerophytes are plants adapted to live in extremely dry conditions. Common adaptations include a thick waxy cuticle which cuts down on water loss because it acts as a barrier to evaporation and also the shiny surface reflects heat and therefore lowers the temperature. Sunken stomata is sunk in pits of the epidermis and moist air is trapped here which lengthens the diffusion pathway and reduces the evaporation rate. Leaf rolled with stomata inside and an inner surface covered in hairs traps moist air and prevents aur movement across the stomata which reduces transpiration. Small leaves which reduce the surface area and therefore the evaporating surface area. Extensive shallow roots allow for the quick absorption of large quantities of water when it rains. Thickened leaves or stems contains cells that store water.
What is natural selection?
Natural selection is when there is a range of genetic variation within populations caused by differences in genes. Organisms then reproduce more offspring than the environment is able to support. This leads to a struggle for survival including competition for resources. Organisms who are best adapted to the environment are more likely to survive and therefore reproduce. These more adapted individuals then reproduce and pass their alleles onto the next generation.
How do populations become more suited to their environments?
Adaptation is the process, resulting from natural selection, by which populations become more suited to their environment over many generations.
What is the development of strains of antibiotic-resistant bacteria an example of?
The development of strains of antibiotic-resistant bacteria is an example of natural selection.
What is selective breeding?
Selective breeding occurs by the selection of individuals (by humans) with desirable features are bred together to produce the next generation in which the offspring show the desirable features. This is down over many generations to achieve the most desirable individual.
What are some differences between natural selection and selective breeding?
