genetic change - mutation Flashcards
How does mutation introduce new alleles into a population?
radiation or chemical mutagens
mutations is only natural source of all new alleles in a species.
mutation resulting in new allele depends on type - somatic or germline mutation, and whether it occurs in a coding or non-coding region of the DNA
mutation
A mutation is any change to the DNA of an organism, that is unpredictable and random.
unpredictable - which gene and how
most have no effect, some result in physical changes
types of radiation
Energy transmitted as electromagnetic waves, including light and heat.
Ionising radiation
radiation that is strong enough to break the bonds between electrons and the nucleus of an atom creating an ion.
high frequency + high energy
direct radiation mutation
where the radiation affects the actual DNA chemistry changing the base sequence.
indirect radiation mutation
where the radiation affects other chemicals in the cell which then damage the DNA structure.
mutagen
Any chemical or radiation that is capable of causing a mutation.
Deaminating agents
Deaminating agents can remove an amino group (containing nitrogen) from a base, turning it into a different base. For example, nitrous acid can convert cytosine into uracil.
naturally occurring mutagens
ionising radiation, UV light, fungus, mold
biological or non-biological
some viruses can even cause mutations
point mutation
A mutation involving a single nucleotide base.
point mutations which affect genes (sections within a chromosome)
base substitution or frameshift
base substitution
A point mutation in which one base is replaced by another.
frameshift
where one base is inserted or removed from the DNA chain shifting all other bases along, changing the amino acids that are coded for.
silent mutations
these have no effect on the protein produced. The new nucleotide still results in the same amino acid being coded for.
missense mutations
these add a different amino acid to the protein that results in the protein being different and may have a deleterious effect. Eg sickle cell anemia.
nonsense mutation
the substitution results in the production of the stop codon which ends protein production. Eg Thalassaemia.
base deletion
The elimination of a single nucleotide from a DNA sequence.
base insertion
The addition of a single nucleotide into a DNA sequence.
frameshift mutation
A significant mutation caused by the deletion of a single base, or a number of bases which are not a multiple of 3.
Structural chromosomal mutations
section of a chromosome is deleted, duplicated, inverted or translocated to another chromosome.
inversion
section of chromosome is inverted (backward)
deletion
A block mutation where a section of a chromosome is lost.
Chromosomal number mutation
A mutation in which a cell contains (whole) extra or missing chromosomes.
aneuploidy
an abnormal chromosome number with either extra or fewer chromosomes than the normal number.
polyploidy
when there multiple sets of chromosomes.
karyotype
A photograph of the chromosomes in a cell, cut out and arranged into homologous pairs.
nondisjunction
The failure of a homologous pair of chromosomes to segregate during meiosis.
germline mutation
A mutation that happens in a gamete or a cell that divides to produce gametes.
Because germline mutations occur in germ cells, they can be passed to offspring.
Somatic mutation
A mutation that happens in a cell that is not a reproductive cell. (body cell)
Somatic mutations may have no effect on the individual at all, depending on the gene that is changed.
non coding regions
refers to a length of DNA which does not contain the coded instructions for protein synthesis. This is either an intron or flanking region of a gene.
Non coding regions of DNA are termed introns.
coding regions
Coding regions of DNA are sections that code for a protein. These are also termed exons.
fertilisation
Sexual reproduction results in variation of offspring because each individual is a result of the fusion of two gametes carrying different alleles for each gene.
This leads to genetic variation.
Because each gamete is haploid then the fertilised cell is the result of the combination of each gamete genetic information
meiosis and independent assortment
Independent assortment of non homologous chromosomes. non homologous chromosomes contain genes for different conditions.
Eg hair colour and skin type.
Non homologous chromosomes can assort in a large variety of combinations leading to increased genetic diversity.
crossing over during meiosis
Crossing over in meiosis further increases variation among the offspring, because it allows the recombination of alleles which have gene loci on the same chromosome.
natrual selection
the most important mechanism of evolution
relies on the existence of genetically-based phenotypic variation in the population
Since mutation is the source of new alleles, without mutation, there could be no natural selection.
genetic drift
There are two ways in which genetic drift can affect the gene pool of a population: the founder effect and a genetic bottleneck.
founder effect
hen a new population is formed from a small number of individuals from an existing parent population, but the genetic make up of these ‘founding’ individuals is not representative of the existing population.
genetic bottleneck
when a population on the brink of extinction grows in numbers again, but the frequency of alleles is changed because the few individuals that survived give rise to the new population which is not representative of the genetic make up of the original population.
gene flow
If a population is not geographically isolated from other populations, then the movement of individuals from other populations into the population is able to
(a) introduce new alleles or
(b) change the frequency of alleles in the population.
