Mutations/Variation Flashcards
Mutation
Is a permanent change to an organisms DNA sequence
Types of gene mutation: point mutation
Point - change to a single base pair including:
Silent Mutation - doesn’t alter any amino acids as certain codons may code for the same amino acid
Types of gene mutations: point mutation - Missense Mutation
Missense Mutation - Alters a single amino acid, single base substitution
E.g.. sickle cell anemia GAG into GTG
Types of gene mutations: point mutation - Nonesense Mutation
Dna creates a premature stop codon, shortening the polypeptide chain
Types of gene mutations: point mutation - frameshift
Insertion/deletion affects every codon beyond the point mutation drastically changing the amino acid sequence
Types of gene mutations: point mutation - Substitution
Substitution ACG
Insertion ATG ATCG
Deletion ATG AG
Inversion ATG to AGT
Physical causes of mutations
Physical mutagens - include various types of energy radiation that cause dna damage, including: hi energy radiation,Uv rays, gamma rays - that directly damage dna structure, double stranded breaks
UV Light - structal distortion by crossing linking nucleotide
X-ray - gene and chromosome aberrations eg. Gaps in double helix, imcorrect bases may be inserted
Nuclear radiation - breaks dna strand, double strand breaks complete breaks in chromosomes, causes overhangs (repaired), no overhangs (mistakes can occur)
Temp - rise in temps can cause hydrogen bonds to break in dna and extreme temps can break phosphodiester bonds
Chemical Mutagens
Mustard gas - Substitution mutation affecting G bases
2-amino purinine, 5-bromaracil - nucleotide subsitution resembles thymine leading to C-G to replaced with A-T
Biological Agents
Invasive pathogens
Viruses - insert their dna through horizontal gene transfer disrupting the traditional function of the cell
E.g. HIV
Bacteria- creates a viral partial, inserts plasmid causes inflammation provoking dna damage
e.g. agrobacterium - causes gall crown disease, inserting Ti
plasmid causing increased cell growth
Transposons (jumping genes) - non coding genes jump from one place to another influencing function of gene
E.g. bacteria antibiotic resistance allowing it jump from dna to plasmid and back
Effects of mutations on survival: Benifical
Change gene sequence (Missense) to create new variations of a trait or (nonesense) eliminates protein that could be harmful
E.g. resistance to HIV by removing surface proteins allowing HIV to enter cells
Effect of mutations on survival: Deletrious/Detrimental
Shorten gene sequence (nonsense) changing the normal function of the trait
E.g. sickle cell anemia
Effect of mutations on survival: Neutral
Have no effect on the function of specific feature (silent mutations)
E.g. Polyploidy plants, show difference in colour or show 2 colours
Type of chromsome mutations: Aneploidy
Addition or loss of one chromosome from cell due to disjunction, failure to separate of homologous pair during meiosis
Fertilisation of gametes with 2 copies will produce a zygote with 3 of chromosome (trisomy) as one parent is missing a chromosome
Type of chromosome mutation: Monoploidy
1 chromosome
E.g. male species of bees are monoploidy produced by pathogenesis, an entire organism regenerated from a single egg
Can be deleterious as there is only one gene
Type of chromosome mutation: Polyploidy
Cell divions that give rise to haploid genes fail altogether , so that half of the gametes contain 2 copies of each chromosome and the rest have none
When fused with normal haploid gametes 3n zygotes formed, if 2 2n gametes fuse tetraploid 4n form
Multiple chromosomes (3n,4n) or none
Can be beneficial- advantageous
E.g. Flowering plants, ferns, algae that are polyploidy can produce higher yield, hardiness and fertility
Change to chromosome structure: Deletion
2 or more double stranded breaks and rearrangement of broken segments. Occur in meiosis - crossing over, moving apart, mutagens
Deletion - double stranded breaks at 2 sections, middle piece falls out, removing genes with it and rejoins
Change to chromosome structure: Inversion
Inversion - reverses normal sequence of genes (rotates 180) and rejoins, results in infertility
Change to chromosome structure: Duplication
Duplication - extra section/copy of chromosome added to same or other chromosome, can be harmful or advantageous
Eg. the various genes used to control haemoglobin in red blood cells arised from duplication
Change to chromosome structure: Translocation
Translocation - section of 1 chromosome breaks off and reattaches with other chromosome, results in cancer loses control over gene
Causes of Mutations
Cell division - unequal crossing over, misaligning during crossing over may gain extra or lose nucleotides
DNA Replication errors - DNA Polymerase inserts the wrong nucleotide. corrosive chemicals containing oxygen, G2 phase repairs - not repaired properly or repaired improperly and mutation becomes a part on the DNA sequence
Variation: Crossing Over
Swapping of genes during this prophase, exchange of maternal and parental homologous pairs creating new alleles
Crossing over occurs at random points and at more than one chiasma point (the point of contact where the chromosomes cross
Variation: Independent Assortment
Random orientation of chromosomes at the metaphase plate during metaphase
Chromosomes line up independently to the other chromosomes
-There are 8 million possible combinations
Variation: Random Segregation
During anaphase 1 the random lining up of maternal and parental chromosomes move to opposite poles of the cells
random separation each gametes ends up with a random selection of maternal and parental gametes
Variation: Fertilisation
Random union of gametes
Brings chromosomes from two different parents creating new combinations of alleles in the offspring - mixing together genetic information 50% from each
Male gametes can fertilise any female gamete resulting in unique combination of maternal and parental genes
Types: internal (humans), external (coral)
Why is mutation the ultimate source of variation?
Due to the formation of NEW alleles and the occurrence being very rare
Arising spontaneously during DNA replication, cell division and non-disjunction, or due to mutagens
