Evolution/ Mutations

Evolution

is the change in characteristics of a species over time, gradual change that occurs over a number of generations

phenotypes

set of characteristics, of individuals are a result of the alleles

Genotype

The combination of alleles for a gene

population

a group of organisms of the same species living together in a particular place at a particular time.

gene pool

is the sum of all the alleles in a given population.

allele frequencies

how often each allele of a gene occurs in the gene pool for that population.

mutant

An organism with a characteristic resulting from a mutation

gene mutations

which are changes in a single gene so that the traits normally produced by that gene are changed or destroyed

chromosomal mutations

in which all or part of a chromosome is affected

induced mutations

mutagens in the environment can increase the chance of mutations occurring

spontaneous mutations

Other mutations occur due to a random error in a biological process such as mitosis or meiosis.

somatic mutation

When the body cells, or somatic cells, are involved with a mutation. only the individual with the somatic mutation is affected.

Missense mutations

cause a change in the amino acid, and therefore in the protein produced.

Nonsense mutations

change the base sequence to the code to STOP.

Neutral mutations

cause a change in an amino acid; however, the amino acid is of the same type

and does not change the structure of the protein enough to change its function.

Silent mutations

do not cause any change in the amino acid, and therefore in the protein

gene mutation

affects only a single gene

chromosomal mutation

affects several genes, may change the structure of a chromosome or the number of chromosomes

Point mutations

are due to changes in a single nucleotide therefore, only one base is changed

point caused by

insertion, deletion and substitution

inserted

a new nucleotide is added to the DNA strand

substituted

an existing nucleotide is replaced with another one, with a different base

deleted

a nucleotide is removed from the DNA strand.

Frameshift

occurs when bases have been added or removed

duplication (or insertion) - a section of chromosome occurs twice

deletion

a piece of DNA is removed

inversion

breaks occur in a chromosome and the broken piece joins back in, but the wrong way around

translocation

part of a chromosome breaks off and is rejoined to the wrong chromosome

non-disjunction

aneuploidy, during meiosis, a chromosome pair does not separate and so one daughter cell has an extra chromosome and one daughter cell has one less than the normal number.

Gene flow

is the movement of genetic material from one population to another.

selective agent

The environmental factor acting on the population

Principles of evolution through natural selection

There is variation of characteristics within a species, More offspring of a species than can survive to maturity, struggle for existence, Individuals with characteristics best suited more chance of surviving and reproducing, Favourable characteristics passed to the next generation, In the gene pool the proportion favourable characteristics gradually increases.

Sickle-cell anaemia

The Anopheles mosquito

Sickle-cell symptoms

including clogged blood vessels (inflexible can become stuck in the blood vessels, causing a blockage), pneumonia, rheumatism, heart disease, inflammation of the hands and feet, and anaemia (sickle-shaped red blood cells often die early, resulting in anaemia), fatigue, jaundice, organ damage (such as to the kidneys, lungs and brain), high blood pressure and heart failure

genetic drift

the random, non-directional change in allele frequency between generations, it is purely by chance. Genetic drift occurs in populations of all sizes; however, it is unlikely to have a significant effect in large populations.

Founder effect

An extreme example of genetic drift occurs when a small group moves away from its homeland to a totally new area and establishes a population, which expands, a different allele frequency from the original population, decreased genetic variation. This means that the new population may show a frequency of features that are not typical of the original homeland population

Bottleneck effect

extreme example of genetic drift, event such as a natural disaster severely reduces the size of the population, allele frequency after the disaster may, by chance, be different from before the event, chance of survival is by chance and not due to a specific trait

species

a group of individuals that share many characteristics and can interbreed under natural conditions to produce fertile offspring

The steps involved in speciation

1 Variation