18 Variation and selection Flashcards
variation
differences between individuals of the same species
what does continuous variation result in
a range of phenotypes between two extremes
example of continuous variation
body length and body mass
what does discontinuous variation result in
a limited number of phenotypes with no intermediates
examples of discontinuous variation
ABO blood groups, seed shape in peas and seed colour in peas
what is discontinuous variation usually caused by
by genes only
what is continuous variation caused by
genes and the environment
mutation
genetic change
how are new alleles formed
by mutations
what increases the rate of mutation
ionising radiation and some chemicals increase the rate of mutation
gene mutation is
a random change in the base sequence of DNA
what are sources of genetic variation in populations
mutation, meiosis, random mating and random fertilisation
adaptive feature
inherited feature that helps an organism to survive and reproduce in its environment
explain the adaptive feaures of hydrophytes
Small roots - don’t need long, can absorb water/mineral ions from surrounding water, mainly used for anchorage.
Large air spaces in leaves - keep the leaf close to surface to float to absorb light for photo
stomata always open - no need to keep closed as constant supply of water
stomata found on upper epidermis - can exchange gas more easily with air
lack of waxy cuticle or very thick one - water loss isnt an issue OR waxy cuticle repels water to keep stomata clear
Lack of xylem - not as much need for water transport, water is absorbed through plant tissues
Floating seeds - for seed disperal away from parent so less competition
explain the adaptive feaures of xerophytes
Rolled up leaves with stomata inside - prevents wind from blowing, traps layer of humid air and reduces water pot gradient
Thick waxy cuticle - reduces evaporation from the epidermis
hairs on underside - trap humid air next to stomata and reduces water pot gradient
needle leaves - reduce surface area
swollen stems - store more water
shallow roots - absorb water from lightest rainfall
deep roots - penetrate to very low water table
describe natural selection
- the individuals within a population show variation. THere is differences due to their genes
- There is production of many offspring
- there is competition for resources between individuals
- There is struggle for survival ebtween individuals
- Only the organisms that are better adapted to the environment will reproduce. ‘Survival of the fittest’.
- The better adapted organism will pass on the more sucessful alleles to offspring of the next generation.
describe selection breeding
- selection by humans of individuals with desirable features
- crossing these individuals to produce the next generation
- selection of offspring showing the desirable features
how long and why is selective breeding by artificial selection carried out
over many generations to improve crop plants and domesticated animals
describe adaptation as a process
resulting from natural selection, by which populations become more suited to their environment over many generations
example of natural selection
the development of strains of antibiotic resistant bacteria
differences between natural and artificial selection
(about natural selection)
- features are adaptive for environment
- features are selected by environment
- there is compeition between individuals for resources
- prescence of predators, cold temps, food availabilty
- slower than artificial selection
- increases the ability to survive and reproduce
- maintains genetic variation/selective reduces genetic variation
- random mating (as opposed to planned mating)
How do some bacteria become resistant to antibiotics
- within a population of bacteria there is variation.
- random mutations in genes can create new alleles that are resistant to certain antibiotics
- the antibiotic acts as a selection pressure and kills the non resistant strains
- there is less competition for resources
- the surviving bacteria will be able to pass their resistant gene to their offspring when they reproduce
- example of evolution by natural selection
