Variation and evolution

Variation

Differences in traits among individuals in a population.

What two factors contribute to variation between organisms

The genes that individual inherited

The environment they are exposed to

Mutation

a change in the dna code

Rarely harmful

Evolution

The process by which inherited characteristics of a population change over time due to natural selection. May result in new species

Who developed and proposed the theory of evolution

Charles Darwin

Survival of the fittest

The individuals with the most favourable characteristics are more likely to survive

Describe how new species are formed

Over a long period of time the phenotype of an organism can change so much because of natural selection that a completely new species is formed

Speciation

-population separated by geographical barrier

-genetic variation occurs due to mutation

-different environmental in two areas

-natural selection occurs where individuals with favourable alleles survive

-they reproduce

-alleles passed down to offspring

-eventually two species cannot breed successfully

What scientist nearly published findings on speciation before Darwin

Alfred Russel Wallace

What is a species

Group of physically/genetically similar organisms that can interbreed to produce fertile offspring

Lamarks theory

Organisms could acquire new traits during their lifetime and could pass these onto offspring

Darwin and Wallace theory

Natural selection is the driving force behind the gradual development of species

Why was theory of evolution not accepted quickly

Religious reasons-went against gods theory

Lack of evidence- scientists didn’t accept theory

DNA hadn’t been discovered yet- better understood now

Selective Breeding

Human-directed breeding for specific traits in organisms.

Genetic engineering process for human insulin

1. Isolate insulin gene from human dna

2. Insert dna into a vector such as plasmid

3. Insert plasmid into host bacterium

4. Let bacteria divide and produce insulin protein

benefits of genetic engineering

increased crop yield and quality

reduce need for pesticides

increased profits

Risks of genetic engineering

-disruption of natural ecosystems

-introduction of diseases

-introduction of allergens and toxins

-creation of biological weapons

-ethical dilemmas

Cloning Techniques

Methods like tissue culture and embryo transplants for replication.

Tissue culture

Take tissue from desired plant (explant)

Sterilise explant

Place in agar plate with growth hormones and nutrients I.e glucose and magnesium

Transfer small masses of cells grown into soil to grow

Plants develop genetically identical to adult plants

-preserves rare species and is quick

Cuttings

-take cuttings from good parents plants

- plant them with growth hormones and produce clones quickly

-cheaper and simpler

Embryo transplants

-sperm cell taken from prize bull and egg cell taken from prize cow

- sperm used to artificially fertilise an egg cell- embryo develops and is split many times before cells become specialised

-these clones embryos can be implanted into lots of other cows which will produce genetically identical calves

Adult cell cloning

1. The nucleus is removed from an unfertilised egg cell

2. The nucleus from an adult body cell, such as a skin cell, is inserted into the egg cell

3. An electric shock stimulates the egg cell to divide to form an embryo

4. These embryo cells contain the same genetic information as the adult skin cell

5. When the embryo has developed into a ball of cells, it is inserted into the womb of an adult female to continue its development

Fossils

Remains of organisms from millions of years ago

Why is the fossil record incomplete

Some organisms are soft bodied so do not fossilise well

Some fossils long ago have been destroyed

Three mains ways fossils form

1. Hard body parts I.e bones decay very slowly so are gradually replaced by minerals to for, rock like substances

2. Animals can leave impressions or casts such as footprints which become covered in layers of sediment and eventually rock

3. Some parts of organisms may not decay at all and are preserved in amber, peat or ice

Extinction

Occurs when no remaining individuals of a species is still alive

Why may a species become extinct

Rapid environmental changes I.e climate change

Reduction in habitat could reduce food and living space

Increased hunting

Antibiotic resistance

When bacteria evolve to become able to survive exposure of antibiotics

How does resistant bacteria arise

A population of a bacteria infect someone

Person takes antibiotics to kill bacteria

bacteria get a random mutation and makes them less susceptible to antibiotic then others

Antibiotics kill all bacteria except those that are resistant

Resistant bacteria reproduce so more mutation may arise

Now there’s an of bacteria that can’t be killed by antibiotics