chapter 19- genetics of living systems Flashcards
what is a mutation
a sudden, significant, random change in the dna of a cell (change in the base sequence of DNA)
a stable heritable change in genetic material.
they introduce an unpredictable form of variation and can lead to the formation of new genes
do mutations occur in all groups of living things
yes
a mutation may be restricted to …… or may even affect a …….. in a cell
a single gene or a number of chromosomes in a cell
what does it mean if a mutation occurs in a somatic cell
somatic mutations are not in gametes and so only affect the organism and cannot be inherited
only true of multicellular organisms
what are germ-line mutations
mutations that occur in gametes and so may be transmitted to future generations in the future
only true of multicellular organisms
Gene mutation occurs spontaneously during DNA replication. However, some external factors can increase the rate of mutation. these factors are called…
mutagenic agents
what are the mutagenic agents
viruses
chemicals
radiation (different types have different effects on living cells depending on the wavelength and dose of radiation)
how and why can a mutation be passed on
if a new gene results from a mutation and confers some form of selective advantage, then when the organism reaches maturity and get a mate it will be more likely to be passed on
over time mutation increases in frequency in the gene pool
what is the effect of radiation on fruit flies eg
radiation will cause a mutation causing vestigial wings
give an example of when a mutation can have a beneficial advantage
and exp
sickle cell anaemia
inherited mutation of a gene that codes for the structure of haemoglobin, causing the rbcs to become sickle shaped (when they encounter low conc of O2)
causing severe pain (rbcs become lodged in capillary beds) and tiredness
in tropical africa mutation gives resistance to a severe form of malaria, therefore mutation was passed on
how is sickle cell anaemia caused
it is as a result of a gene mutation the mutated gene (haemoglobin S) is recessive
so only HOMOZYGOUS RECESSIVES suffer
how is the is a rbc changed in shape with sca
there is a base substitution on the dna sense strand which now codes for abnormal Hb, that changes the mrna strand as it is complementary which results in a different protein being produced as a result and so the Hb molecule has an abnormal shape
What is a substitution mutation?
A substitution mutation is when a nucleotide is swapped out for a different one - a point mutation, the other nucleotide contains a different base
occurs as an error during dna replication
only one base codon is affected > one aa changed at specific position within the final polypeptide
can have a minor or serious consequence if the proteins shape is affected.
examples of conditions which result from point mutations
sickle cell anaemia (sub)
cystic fibrosis
colour blindness (red/green) - sexlinked
some cancers (base sub in tumor suppressor genes)
these are differences in the phenotype
explain why colour blindness is more common in males than females (2)
it is caused by a recessive allele on the x chromosome
males only need one recessive allele and females need two recessive alleles to be colour blind
what are the 3 results of point/sub mutations
silent (dk it occurs), nonsense > stop = codes for nothing (cant make rest of the protein), missense (conservative/non)(has different 3d shape)
why would a base substitution in a dna triplet may not alter the amino sequence of a protein
because the genetic code is degenerate as there is more than one codon for most of the amino acids so it will still code for the same amino acid
What is a deletion mutation? and what does it result it
A deletion mutation is when a nucleotide is removed from a DNA sequence (usually irreversible, unlikely to be undone by an insertion)
causes frame shift > altering all of the base triplets downstream from the mutation within the reading frame (more impact potentially every aa after mut will be different)
greatest effect on the structure of the protein, often leads to the formation of non-functional proteins
what happens when 3 bases are deleted
it doesnt alter the reading frame but does result in the loss of an amino acid from the final polypeptide chain
What is an insertion/addition mutation? and what are they caused by
An insertion mutation is when a nucleotide is added to a DNA sequence
caused by errors during replication of repeating elements (rg AT repeats) or caused by transposable elements (therefore they can be reversed by excision of the TE)
if the genetic information transported from the dna to the ribosomes for protein synthesis by mutation then the …. structure is altered
what other structure is also altered
primary
tertiary and
quaternary (potentially)
what is albinism and how is it caused
inability of cells to form the pigment melanin because a mutation of the gene that codes for an enzyme involved in the chemical pathway leading to melanin results in the loss of the enzyme
what disadvantages comes with albinism
lack of camouflage > death
lack of UV protection > death
die before maturity so not an advantage and more likely to not pass on gene so not that common
Which types of gene mutation lead to frameshift?
insertion
deletion
not sub cus it only changed one single nucleotide. at most it would change the aa one triplet codes for, it wouldt cause a change in the entire sequence of base triplets
