chapter 18: variation and selection Flashcards
(16 cards)
describe variation
differences between individuals of the same species
describe continuous variation
- range of phenotypes for a particular characteristic between two extremes
- caused by genes and environment
describe discontinuous variation
- limited number of phenotypes with no intermediates
- usually caused by genes only
- seed colour and seed shape
describe gene mutation
a random change in the base sequence of dna resulting in genetic change
how are new alleles formed?
random mutation of genes which causes a change in the sequence of bases
how can the rate of mutation be increased
with ionisinf radiation or chemicals
state sources of genetic variation
- faulty separation of chromosomes during meiosis
- faulty replication of chromosomes during meiosis
- mutation
- random mating
- random fertilisation
describe an adaptive feature
an inherited feature that helps an organism to survive and reproduce in its environment
describe the adaptations of hydrophytes
- many air spaces in spongy mesophyll layer to reduce its density and increase buoyancy to better absorb energy from light for photosynthesis
- many stomata found on upper epidermis since only upper epidermis exposed to air; many stomata since it does not need to conserve water, stomata always open
describe the adaptations of xerophytes
- thick waxy cuticle: to prevent loss of water, shiny surface reflects heat
- sunken stomata: reduces evaporation rate
- rolled up leaf with inner surface covered in hairs: traps moist air and prevents air movement across stomata, reduces transpiration
- small leaves: reduce evaporating surface
- extensive shallow roots: quick absorption of large quantities of water when it rains
- thick stems: contain cells that store water
- spikes: prevent herbivores from consuming them
describe natural selection
- individuals of a population show genetic variation
- production of more offspring than environment is able to support
- strugfle for survival, competition of resources
- individuals with characteristics most suited to the environment are better fit to survive and reproduce
- alleles resulting in these characteristics are passed to their offspring of the next generation
describe adaptation
the process resulting from natural selection by which populations become more suited to their environment over many generations
describe evolution
a change in adaptive features of a population over time as a result of natural selection
how do bacteria become resistant to antibiotics?
- random mutations occur in the genes of bacteria
- genetic variation occurs, bacteria may gain the ability to be resistant to the antibiotic
- resistant bacteria live longer and have more chances to reproduce
- resistant alleles passes on to offspring
- frequency of resistant alleles in bacteria increase
- natural selectiom occurs as the bacteria become better adapted to the environment
describe selective breeding
- selecting individuals with desirable characteristics and breeding them together
- offspring that do not show the desrired characteristics are selected and bred together because its not likely all the offspring will show the desired characteristics
- repeated for many generations until the offspring consistently show the desired characteristics
compare natural and artificial selection
- natural has its selection pressure come from environmental conditions; selection has its come from humans
- natural produces characteristics suitable to the environment conditions; selection produces desirable characteristics to humans
- natural affects many characteristics, artificial usually only one or a few
- natural is much slower; artificial is faster
- natural is for adapting to environment; artificial is for economical/aesthetic reason
