Chapters 18 igcse bio 2024

pov: bio

Variation

Differences between individuals of the same species

Discontinuous Variation

Qualitative, result of genes only not affected by the environment, limited number of phenotypes

Continuous Variation

Quantitative, a result of the combined effect of genes and the environment, ranges between two extremes

Example of discontinuous variation

Blood groups

Examples of continuous variation

Height

Phenotype =

Phenotype = genotype + environment

How does a mutation happen

Mistakes in copying DNA as cells get ready to divide - pairing with the incorrect base

damage to the DNA- Some environmental factor might alter the bases present in the DNA

uneven distribution of chromosomes during the division of cells

Difference between Chromosome mutations and gene mutations

Chromosome mutations happen when cell division doesnt work properly, consequences are serious

Gene mutations occur when part of the base sequence of the DNA has been changed

What increases the rate of mutation

Radiation-gamma, ultraviolet and X-radiation can damage DNA

Chemicals-tobacco smoke and plant control hormones can cause mutation

Sources of genetic variation within populations

mutation, meiosis, random mating and random fertilisation

Adaptative organism

An organism that is well suited to make the most of the limited resources within its environment is said to show adaptation

Adaptative feature

An inherited functional feature of an organism that increase its fitness

How does evolution happen

Through natural selection where those without a certain trait slowly get killed

Different ways natural selection occurs

Over-production:

Struggle for existence

Variation

Survival of the fittest

Advantageous characteristics are passed on to offspring because those who have the characteristic breed

Difference between lamarck and darwin

Darwin believed that the environment killed those off without the characteristic.

Lamarck believed that the animals got certain traits because of the environment

Articial selection

When those that have the most useful characteristics breed

Examples of artificial selection

Jersey cattle have been bred to produce milk with a very high cream content. Domestic dogs are the same species but bred for different tasks. Wheat has been bred so every one is the same height.

Adaptation

The process, resulting from natural selection, by which populations become more suited to their environment over many generations

What happens in selective breeding

Once a plant breeder has bred a plant with a desirable characteristic then asexual reproduction must be used to make many copies of it.

Artifical vs natural selection

In artificial selection humans are the agents of selection while natural selection relies upon the natural environment

Artificial selection is much quicker than natural selection since no sex

Artificial selection offers no advantage to the animal or plant in its natural environment