B9- Genetic diversity and Adaptation ✅

what is genetic diversity?

number of different alleles of genes in a population

what are alleles and how do they arise?

• different version of the same gene ( same locus ) → different DNA base sequence

• arise by mutation

what is a population?

• a group of organisms of the same species in a particular space at a particular time

• that can interbreed to produce fertile offspring

explain the importance of genetic diversity

• enables natural selection to occur

• because in certain environments, a new allele of a gene might benefit its possessor

• by resulting in a change in the polypeptide coded for that positively changes its properties

• giving possessor a selective advantage ( increased chances of survival and reproductive success )

define gene pool

The sum of all the alleles of the genes in a population (of a single species) at a particular time.

define allele frequency

How often different alleles occur in the gene pool of a population

name and explain 3 ways how genetic diversity within a species is increased

1. mutation- produce new alleles

2. meiosis- Independent segregation & crossing over give rise to

   new combinations of existing alleles

3. fertilisation- random fusion of gametes

name 3 ways how genetic diversity within a species can be decreased

• Certain events e.g. Genetic bottlenecks and founder effect

• Inbreeding

• Genetic drift

describe the process of natural selection

process by which organisms that are better adapted to their environment survive and reproduce in greater numbers, resulting in the increase of the frequency of the advantageous allele within the population.

Explain the principles of natural selection in the evolution of populations:

M.A.R.I.A

• random mutation causes genetic variation within population

• The environment applies a selection pressure

• in [named] environments, the new allele might benefit its possessor [explain why] → organism has a selective advantage

• Better adapted organisms with the advantageous allele survive and reproduce

• Pass on their advantageous allele to their offspring = increased reproductive success

• Over many generations, the frequency of the advantageous allele increases within the population.

* name new advantageous allele

* use info in question when answering

what is evolution?

• Change in allele frequency over many generations in a population

• Occurring through the process of natural selection

give 2 factors that majorly contribute to evolution and contribute to the diversity of living organisms

adaptation and selection

name 3 examples of selection pressures an organism might face due to their environment

● Competition

○ for food, mates & shelter (animals)

○ for light intensity & mineral ions (plants)

● Disease

● Predation e.g. better camouflaged individuals catch the prey/or escape the predator!

describe 3 types of adaptations

Natural selection results in species that are better adapted to their environment:

• Anatomical - structural / physical features that increase chance of survival

• Physiological - processes / chemical reactions that increase chance of survival

• Behavioural - ways in which an organism acts that increase chance of survival

give an example of an anatomical adaptation

larger ears for heat loss in desert

give an example of an physiological adaptation

animals that produce better venom don’t get eaten

give an example of an behavioural adaptation

bird migration

name 2 types of natural selection

1. directional selection

2. stabilising selection

Stabilising selection

example: human birth weight

who has selective advantage: organisms with an average / modal variation of a trait eg. babies with an average weight

• selects for average

• selects against extremes

environment: stable

effect on population over many generations:

• reduced variability and size of range within population due to increased frequency of organisms with alleles for average trait

• normal distribution curve similar, less variation around mean

directional selection

example: antibiotic resistance in bacteria

who has selective advantage: organisms with extreme variation of a trait eg. bacteria with high level of resistance to a particular disease

• selects for extreme

• selects against average

environment: change eg. antibiotic introduced

effect on population over many generations:

• increase frequency of organisms with alleles for extreme trait

• normal distribution curve shifts toward extreme trait

how can natural selection result in antibiotic resistance

• some bacteria have an allele for resistance due to random mutation

• exposure to antibiotics is selection pressure

• non resistance bacteria die

• resistant bacteria survive and reproduce

• Frequency of resistance allele increases in population of bacteria

Directional versus stabilising selection graphs: