Human Bio- mutations/natural selection

what is a mutagen

an environmental agent that increases the rate of mutation

what is a mutation

A permanent change in gene or chromosomes leading to a new characteristic in an organism. they can occur randomly or be induced.

what are the 2 types of mutation and describe

• Chromosomal: a change in the number or structure of chromosomes in an organism. they affect larger portions of DNA sections

• Gene: is when an alteration occurs to a single gene so traits produced are changed or altered

what is point mutation

point mutations is a type of gene mutation that is due to the changes in a single nucleotide so only one base is changed.

what are the 2 ways genes change

point mutation or frameshift

what are the 3 types of point mutation

• insertion: a new nucleotide is added to the strand

• deletion: a nucleotide is removed from the strand

• substitution: existing nucleotide is replaced with another one, with different base.

what is frameshift mutation

• is a result from point mutation

• occurs when bases have been added removed.

• this results in the series of 3 bases that code for amino acid starting at different base which affects outcome for all DNA onwards

• they only code for one or less amino acid but rest are the same

what are the 5 types of chromosomal mutations

• duplication: selection of chromosomes occurs twice

• deletion: piece of DNA is removed

• inversion: break occurs in chromosome but piece joins back in but in wrong way around

• translocation: part of a chromosome breaks off and is rejoined to the wrong chromosome.

• non disjunction: during meiosis, chromosome pair doesn’t separate at centromere so one daughter cell has extra chromosome while one has less

how do you classify mutations

by their causes, location, effect, number of DNA affected and the change in the DNA

describe the heritability of mutations

• there are 2 ways which the mutation can be inherited

  1. Somatic: somatic mutation when the mutation occurs in the body (somatic cells). this means the individual is only effected but not passed on to offspring. e.g cancerous growths. can be chromosomal or gene

  2. Germinal/germline: when mutation occurs in the gamete cells. this means the individual isn’t effected but the mutation will pass onto offspring. it is often naturally aborted if fertilised. e.g phenylketonuria (PKU). can be chromosomal or gene

what are the ways the mutations can effect the body

1. Missense: cause change in the amino acid and therefore the protein produced

2. nonsense: change the base sequence to code for STOP which means synthesis of the protein will stop making a shorter protein and unlikely to be able to fulfil its function

3. Neutral: cause a change in an amino acid but the amino acid is of the same type and does not change the structure of the protein enough to change its function.

4. Silent: do not cause any change in the amino acid as the protein produced as most amino acids are coded by multiple base sequences.

define population

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

define gene pool

the sum of all alleles in a given population. double the population or add up all individual letters

define allele frequency

the proportion of a given allele within a gene pool. each individual letters percentage

define and give examples of mutagens/mutagenic agents

• substances that increase the rate of mutation.

• e.g:

  - chemical: carcinogens, cosmetics, preservatives

  - Radiation: UV, X-Rays

  - infectious agents: viruses, bacteria

how do mutations occur

• mutagenic agents: substances known to increases the rate of mutation

• DNA replication: an error occurring during the process that alters DNA code

• cell division: an error that occurs during process that that alters genes or chromosomes produced.

why is mutation important

it introduces new and different alleles into gene pool. if a new allele helps individuals survive there will be a change in gene pool and pass onto offspring

define natural selection

is the process by which a species becomes better adapted to its environment. those individuals that have the favourable characteristic will have a survival advantage and pass on characteristic to offspring.

how is natural selection shown in an environment

• natural selection is the process by which a species becomes better adapted to its environment.

• there is already variation naturally in the population by the different phenotypes (name phenotypes in question)

• the organism with the favorable characteristic will have a survival advantage

• they are then able to live to reproductive age

• they are able to produce more offspring and pass on favourable characteristic to subsequent generations

• therefore increasing the allele frequency of favoured characteristic and increases the presence of the characteristic.

describe random genetic drift.

• is the random, non directional change in allele frequency between generations

• it commonly happens in smaller generations as there is a smaller number of breeding partners.

• it is random and not linked to survival

• alleles that are rare in larger population can by change be more common in a smaller population

what are the 2 examples of genetic drift

1. Founder effect: when a small group moves away from population and establishes its own community.

   • the small population may not be a genetic representation of parent group due to different allele frequencies and decreased variation.

   • therefore the result in allele frequencies will differ from parent population.

2. Bottleneck effect: when an event like a natural disaster severely reduces the population. after this event, allele frequencies, by chance, can be different than before the disaster.

how does migration effect variation

• migration, when new organisms enter population, brings gene flow

• gene flow is the transfer of alleles from one population to another.

• immigrants being new alleles not already in population which changes allele frequency.

what are some barriers to gene flow

• geographical: oceans, mountains, rivers, deserts

• Sociocultural: tend to procreate with people who are similar to us (class, status, religion, educational background)

what is Dawrins theory and what was it based off

• Darwin had the theory of natural selection and evolution.

• it was based off 3 observations:

  1. Variation:

     • variation is the difference that exists between individuals or the population of a species.

     • it naturally exists in a population of species.

     • there is genetic diversity so not all organisms have the same phenotypes due to their different genotypes.

     • darwin noticed that all species members vary slightly and noticed that it was passed on to their offspring.

2. Birth rate/limited resources.

   • organisms reproduce faster than the rate at which food and other resources increase

   • therefore there is a struggle for existence (organisms compete for the limited resources to survive.

3. natures balance: each species numbers tend to remain relatively constant

• this led to Darwin realising that there must be a struggle for existence to survive, and because there was a range of variation within species population, those with the best suited characteristics would survive and were ‘fitter’ than the others.

• those that has the favourable characteristic would be able to live to reproductive age and have offspring to pass in the characteristic while the others would die before being able to pass on the trait.

what is a selective agent

• any factor that causes the death of an organism with certain traits but has no effect on the individuals without those characteristics

what is sickle cell amenia

• is caused by a point mutation that results in sickle shaped RBCs

• AA- normal cells has no effect in non malaria zones but will get malaria in malaria zones

• AS- will have the sickle cell trait and has heterozygous advantage in areas of malaria but no effect is areas of non malaria zones. In malaria zones they will survive to reproductive age and will pass on the trait to offspring

• SS- has the sickle cell amenia and will decrease the O2 carrying ability

describe Tay-Sachs disease

• is a lipid metabolism disorder that is a lethal recessive disease.

• it has the heterozygous advantage as they have reduced amount of enzyme that stops destruction of neurons, some protection against tuberculosis.