variation and selection Flashcards
variation
differences between the individuals of the same species
discontinuos variation
variation in which there are distinct categories of phenotype, with no intermediates
e.g. eye colour
caused by genes
only genes are passed on to their offspring
population
a group of organisms of one species, living in the same area at the same time
continuous variation
variation in which there is a continuous range in phenotypes between two extremes
e.g. height
caused by genes and environment
bars in a histogram…
touch
mutation
a random change in a gene (base sequence) which can produce new alleles; mutation involves change in the base sequence
only source of all genetic variation
are random
mutagens
chemicals which can cause mutation
what does the base sequence in DNA determine
amino acids sequence in the proteins that are made in a cell
change in protein made
most of the time the mutation is harmful
adaptive feature
an inherited feature that helps an organism to survive and reproduce in its environment
caused by genes
xerophyte
a plant that has adaptive features that help it to survive in an environment where water is scarce:
- closing stomata
- waxy cuticle
- hairy leaves
- sunken stomata on underside of leaves
- reducing the surface area of the leaves
- having deep or spreading roots
adaptive features : closing stomata
plants lose alot of water through there stomata so by closing them it stops transpiration
however, the plant cant photosynthesis bc CO2 cant diffuse into the leaf
adaptive features : waxy cuticle
made by the cell in the epidermis
wax makes the leaf waterproof
adaptive features : hairy leaves
hairs trap a layer of moist air next to the leaf, reduces diffusion from water vapour from the leaf to the air.
adaptive features : sunken stomata on underside of leaves
the lower surface of the leaves a usually cooler so less water will evaporate
stomata may be sunk into pits in the leaf , the air is collected and trapped in the pits this reduces the diffusion so less water diffuses
adaptive features : reducing the surface area of the leaves
smaller surface area means less water diffuses out of it.
adaptive features : having deep or spreading roots
to seek water which is usually very far away
hydrophytes
a plant that has adaptive features that help it to survive in water
water hyacinth adaptive features
roots dont attach to the bed of the river or pond but float freely in the water
the stems and leaf stalks have hollow spaces in them filled with air, which help them to float on the top of the water where they can have plenty of light to photosynthesis
stomata on the upper surfaces of the leaves , contact to air for diffusion and photosynthesis. doesnt need to close the stomata if hot bc has enough water
cabomba adaptive features
live completely underwater
thin leaves may be feathery
feathery leaves spread out easily in the water so each leaf has plently of water. also helps them float
natural selection
a process in which individuals with advantageous features are more likely to survive, reproduce and pass on their alleles to the next generation
natural selection steps
- variation: there is variation in the population of orgamnisms. some of these variation is caused by having diff. alleles
- overproduction: many more offspring are produced than will survive to become adults and reproduce
- best adapted individuals more likely to survive and reproduce:
- alleles that confer useful adaptions more likely to passed on
2 reasons as to why natural selection can cause change in the population
a new allele arises: by mutaiton. this allele gives an organism a better adaptive feature this organism will then reproduce and pass this allele on to their offspring
environment change (climate) causes that the once useful to survive are no longer useful. individuals that do have a adaptive feature survive and pass on their alleles.
selection pressure
something in the environment that affects the chance that individuals with different features will survive and reproduce.
adaption
the process, resulting from natural selection, by which their populations become more suited to their environment over many generations
drugs
any substance taken into the body that modifies or effects chemical reactions in the body.
to recover or help minimize symptoms.
antibiotics
a substance that is taken into the body, and which kills bacteria but does not affect human cells or viruses.
medicinal drugs
cures bacterial infections
antibiotic resistance
over the last few decades, many populations of pathogenic bacteria have become resistant to antibiotics. this happened by natural selection. these resistant bacteria are no longer killed by antibiotics
penicillin
an antibiotic that stops bacteria from forming cell walls. when treated with penecillin the bacteria are unable to grow new cell walls and they burst open
staphylococcus aureus
lives under the skin of most of us
normally harmless
sometimes cause dangerous infections if into the body
in the past it was easy to treat this including penicillin but now they are resistant given the name MRSA
barely any antibiotics that can kill it.
how is a new species produced
more and more mutations occur in the DNA base sequences causing the DNA to become so different to the population that they can no longer breed with the orgininal species.
bioligist use this to wokr out how closely related they are and then classify.
selective breeding
choosing particular organisims with desired characteristcis to breed together, and continuing this over many generations.
selective breeding steps
- choose the organisms the has the desired characteristics
- choose another organism whose mother or sister or daughter had the desired characteristic
- breed them
- from the offspring choose the best one and breed with the chosen organism.
- repeat.
differences in natural selection (N) and selective breeding (S)
N- environment determines which organisms survive and breed. in S humans do this
N- random mating, S- humans determine this
N- adaptive features is what determines the selection, S- we dont necessarily choose the adaptive features just the ones we want.
N- more variation in the pop., S- much less
N- speed of change in pop is slow. S- larger changes in shorter periods of time.
