Selection and Evolution Flashcards
describe the difference between continuous and discontinuous variation
continuous is phenotypic characteristics that change over a range of values (environmental/genetics)
discontinuous is distinct categories with no intermediates (genetics)
describe genetic variation
independant assortment of chromosomes;
crossing over between between chromatids;
random mating between organisms in species;
random fertilisation of gametes;
describe mutation
a random change in DNA sequence by insertion/deletion/silent stop codon gives shorten polypeptide does not code for amino acid mutation passed down if it is in ovaries/testes
describe environmental variation
access to nutrition
exposure to pollutants
disease
horizontal gene flow
how does continuous variation occur
different alleles at single gene locus have small effects on phenotype
polygenes needed for observable variation
how does discontinuous variation occur
different genes have large effect on phenotype
definition of natural selection
fittest organisms has its alleles with advantages passed down to offsprings
examples of biotic factors
predation
infection
competition for food
examples of abiotic factors
humidity
overcrowding
light
temperature
definition of fitness
capacity of an organism to survive and transmit its genotype to its offspring
definition of selection pressure
increase/decrease chances of alleles being passed down
definition of negative/positive selection
variations reduce/increase fitness less/more likely to be passed on
definition of balancing selection
more than one variation that increases fitness
definition of sexual selection
traits passed down only for obtaining mate
how does resistance in mosquitoes arise?
mutation;
selection pressure;
resistant mosquitoes have selective advantage;
survive + reproduce;
resistance alleles passed on;
increase in frequency of resistant allele;
definition of evolution
changes in allele frequency in a population, due to natural selection it gives some alleles a better chance of survival
three types of selections
directional
stabilizing
disruptive
describe directional selection
for on extreme trait
against other extreme
describe stabilizing selection
for moderate traits
against both extreme
describe disruptive selection
for both extremes
against moderate traits
describe antibiotic resistance
bacteria has allele resistant to pencillin
acts as selective advantage
reproduce and survive
describe industrial melanism
changing environmental factors acts as selection pressure of moths
having black colour is selective advantage
describe sickle cell anemia
genetic drift - heterozygous sickle cell anemia survive and reproduce - don’t suffer from malaria/sickle cel;
definition of genetic drift
change in allele frequency that occurs by chance, because only some reproduce
what is the hardy weinberg principle
frequency of genotype is its proportion of total population
p^2 + 2pq + q^2
p + q = 1
when does the hardy weinberg principle not apple
mutation migration non-random mating occurs population is small selective pressure occurs against one of the alleles asexual reproduction organism is haploid
why do unreleated species have similar characteristics
had similar selection pressure;
allow organisms to escape predators;
allow organisms to find food;
describe selective breeding of animals/crops
Humans select crops/animals with desirable characteristics to breed;
Desirable characteristics (animals: higher product yield/more meat/ plants: higher yield, disease-resistant)
Over several generations;
Select offspring with desirable characteristics;
Frequency of desirable allele increases;
effects of inbreeding and hybridisation in maize
maize inbred had smaller + weaker generation = inbreeding depression
outbreeding is better
definition of darwin-wallace theory of evolution
organisms change over time due to atural selection of fittest organisms with selective advantages, which are able to survive and reproduce
definition of species
a group of organism (similar physiological features) which can interbreed to produce fertile offspring and are productively isolated from other species
describe prezygotic isolation
individuals not responding to mating behaviour
animals physically unable to meet
inability for gametes to fuse
describe postzygotic isolation
failure of cell division
offspring that will soon die
types of speciation
allopatric
sympatric
describe allopatric speciation
geographical isolation causes barrier = same species don’t mix - features become different cannot interbreed = new species
describe sympatric speciation
polypoid organism has more than two complete sets of chromosomes in cells - meiosis goes wrong
types of reproductive isolation
prezygotic
postzygotic
describe why new species arise from geographical isolation
no gene flow; different selection pressures; different mutations; some mutation s make individuals better adapted; those individuals survive/reproduce; pass on advantageous alleles; many generations
what are the two ways of molecular comparisons between species
comparing amino acid sequences of proteins
comparing mtDNA
describe comparing amino acid sequences of proteins
more similar = more closely related species are;
more similar = more recent common ancestor;
describe using nucleotide sequences of mtDNA
inherited from mother; recombination doesn't occur; mutations constantly occur; mtDNA mutates faster; many copies of mtDNA; no histones; analysis is quicker;
what causes extinction
climate change
increased competition
habitat loss by humans
deforestation
