what is variation and selection Flashcards
what is variation
differences between individuals of the same species
how is phenotypic variation caused
Phenotypic variation is caused by both genetic and environmental factors
what is continuous variation
Continuous variation is influenced by genes and environment, resulting in a range of phenotypes between two extremes, e.g. height in humans
what is discontinuous variation
Discontinuous variation is caused by genes alone and results in a limited number of distinct phenotypes (e.g. you are either blood group O, A, B or AB, nothing else)
what is a mutation
genetic change
what is a gene mutation
a change in the base sequence of DNA
how are new alleles formed
Mutation is the way in which new alleles are formed
what affects the rate of mutation
Ionising radiation and some chemicals increase the rate of mutation
what is down syndrome
Mutation is a source of variation e.g. in Down’s syndrome, where a parent’s chromosomes are unevenly distributed in meiosis. In fertilisation, a zygote with a number of chromosomes that is not 46 is created (e.g. 23 + 24). Characteristics: broad forehead, short neck, downward-sloping eyes, short nose and mental retardation.
what is sickle cell anaemia
Disease in which the red blood cell has a sickle shape instead of a round biconcave shape, controlled by a recessive allele, which causes weakness, aching joints and poor circulation.
The fact that it is recessive means that a heterozygous person can be a carrier: they have the allele but it is not expressed.
sickle cell anaemia and malaria relation
Being a carrier of sickle cell anaemia makes you resistant to malaria
In equatorial Africa, being sickle cell anaemic causes death, malaria causes death, but the carriers have immunity to malaria and have some symptoms of anaemia, in severe cases they are very weak.
what are adaptive features
inherited feature that helps an organism to survive and reproduce in its environment
the inherited functional features of an organism that increase its fitness
what is fitness
the probability of an organism surviving and reproducing in the environment in which it is found
what are xerophytes
live in deserts where water is scarce and evaporation is rapid, or in windy habitats.
features of xerophytes
Deep roots to reach water far underground
Leaves reduced spines with minimum surface area for transpiration
Shallow spreading roots to collect occasional rain
Rolled leaves, leaf hairs and stomata sunk in pits to trap moist air
Waxy leaf cuticle, impermeable water
Stomata opening at night and closed at midday when evaporation is highest
E.g. cactus and marram grass
what are hydrophytes
live in wholly or partly submerged in water
features of hydrophytes
Leaves are highly divided to create large surface area for absorption and photosynthesis
Very little cuticle formation
Lack of xylem tubes, no stomata underside of leaves
Stomata is in the upper surface, has a thick waxy layer to repel water and to keep the stomata open and clear
Roots are often reduced and root hairs are often absent
what is natural selection
- The greater chance of passing on of genes by the best adapted organisms.
- The surviving organisms reproduce, since they don’t get eaten up, so variation has caused the species to evolve.
- Evolution is caused by natural selection which is caused by a change in the environment
how does variation lead to natural selection
Variation is natural or random changes in all living organisms.
Variation leads to survival of the fittest since the variations in certain organisms allow that organism to have an advantage over the others in its species in that area
what is artificial selection
Is breeding organisms with valued characteristics together in order to try to produce offspring which shares those useful characteristics (selective breeding).
Can be used to produce organisms which are more economically valued
what is selective breeding
Selecting by humans of individuals with desirable features
Crossing three individuals to produce the next generation
how are antibiotic resistant bacteria formed
Strains of antibiotic-resistant bacteria are developing as the use of antibiotics is increasing.
In a group of many bacteria, one might mutate to be resistant to the antibiotic, as a result it reproduces and the others die making a new strain of bacteria, which is resistant to antibiotics.
The susceptible (weak) bacteria are killed first
Only resistant (strong) bacteria are left
