mutations

Question 1

what is a mutation

Answer 1

a change in the nucleotide sequence

Question 2

what is mutagenesis

Answer 2

the process of mutation generation

Question 3

how can DNA damage occur not due to chemicals e.c.t

Answer 3

can occur spontaneously e.g spontaneous reanimation from cytosine to uracil

Question 4

what is the problem with spontaneous deamination

Answer 4

c is deaminated to a U. this is then replicated to by DNA replication to make a strand with CG and UA. The UA can be recognised as incorrect however, if this replicated itself again by DNA replication a T will bind to the A. This is normal and not recognised and is a mutation

Question 5

sources of mutations

Answer 5

chemical, anticancer agents, free radicals, ionising agents, spontaneous, DNA replication defect, transposable elements. If these slip through repair mechanism net then cause mutation

Question 6

what are transposable elements (transpons)

Answer 6

cause mutations but no physical to DNA. are DNA sequences that move as unit and move to random sites within the genome an therefore able to change DNA sequence causing mutation

Question 7

what is the problem with transpons

Answer 7

the fact that it can move from donor DNA to recipient DNA and if the transpon inserts itself into a gene then it will cause a mutation. the bigger the gene the more chance that a TE enters gene. may activate if exits or inhibit if enters

Question 8

what does mutation cause

Answer 8

may or may not case phenotypic change. can be good or bad and is driving force of evolution.

Question 9

what is a SNP

Answer 9

single nucleotide polymorphism. - variation of single nucleotide. can have anonymous(no known effect), noncoding SNP(outside of gene) and a coding SNP(inside gene)

Question 10

types of small scale mutation

Answer 10

deletion, insertion and substitution

Question 11

types of large scale mutation (chromosomes)

Answer 11

deletion - portion of DNA is deleted
duplication portion of chromosome is duplicated and put in other chromosome
inversion - 2 parts of chromosomes swap sides
substitution - 1 portion substituted for another
translocation- 1 part of chromosome joins another chromosome

Question 12

what can a mutation cause

Answer 12

may cause change in amino acid and therefore and change in polypeptide or may cause frameshift which results in all the amino acids being wrong and an incorrect polypeptide. can change amount of product, change it overall of change polypeptide length. can also not change it at all.

Question 13

2 types of substitution

Answer 13

transition - same type of base e.g purine to purine

transversion - change to different type of base e.g purine to pyrimidine

Question 14

which bases are purine and which are pyrimidine

Answer 14

purine = A and G 
pyrimidine = T and C

Question 15

what is the sickle cell mutation

Answer 15

mutation of HBB gene. substitution of 1 base causing glutamine to be changed to a valine in the mutated version. is a missense mutation

Question 16

what happens to methionine in gene once translated

Answer 16

in many proteins it is chopped off therefore the 4th triplet code may be the 2nd amino acid in the sequence

Question 17

what does missense synonymous and non-sense mean

Answer 17

missense= substitution causing a change in amino acid, synonymous= substitution which has no effect and non-sense= substitution causing an early stop codon

Question 18

how can a protein been made longer

Answer 18

frameshift means stop codon isn’t read until it finds stop codon later down. can also happen to it making it shorter

Question 19

what are non-sense mutations

Answer 19

when a single base substitution causes a stop codon to be coded and translation is stopped early

Question 20

what are +1 and -1 frameshift

Answer 20

\+1= base inserted
-1= base deleted

Question 21

how can mutations change the amount of gene product

Answer 21

mutations can affect regulatory sequences and therefore alter promoter activity, alter translation by having another AUG, prevent mRNA splicing or reduce mRNA stability and may change how much is then translated.

Question 22

what is an ednouclease

Answer 22

able to make cuts in middle of polynucleotide sequence

Question 23

what is an exonuclease

Answer 23

able to cut of end portions of polynucleotide sequence

Question 24

what is special about deletion of multiples of 3 DNA nucleotides being inserted or deleted

Answer 24

no frameshift. add whole sequence and therefore may still be ok BUT may also affect critical site of gene. message no longer read properly

Question 25

what is robertsonian translocation?

Answer 25

acrocentric (small P arm) chromosomes break at centromereand 2 P arms are lost because so small and the others will fuse together. therefore 45 chromosomes instead of 46

Question 26

what are isochromosomes

Answer 26

2 P arms joined together, q arms are lost or the other way round

Question 27

what are ring chromosomes

Answer 27

both ends of chromosomes have fused together to form a ring

Question 28

what are marker chromosomes

Answer 28

extra chromosome made out of funny small bits

Question 29

what is polyploidy

Answer 29

more than 2 chromosomes per set

Question 30

what is polyspermy

Answer 30

2 sperms fertilise 1 egg

Question 31

what is triploidy, how is it caused

Answer 31

gain of haploid set of chromosomes meaning there are 3 of each chromsome. often not viable and cause miscarriage and most commonly caused by polyspermy

Question 32

what is aneuploidy

Answer 32

abnormal number of chromosomes in cell

Question 33

types of aneuploidy and what its caused by

Answer 33

trisomies - 3 chromosomes instead of 2 (downssyndrome-21) or monosomies (turners syndrome-45,X. only 1 X) - where there is 1 instead of 2 chromosomes in a set. caused by non-disjunction

Question 34

what is non-disjunction

Answer 34

failure of homologous chromosomes or sister chromatids to separate during meiosis

Question 35

what is mosaicm

Answer 35

presence of 2 cell lines over whole body or in specific tissues and is caused by non-disjunction in mitosis

Question 36

why do you do cytogenetic testing

Answer 36

testing of chromosomes
accurate diagnosis, better clinical management, assess future poductive risks ( prevent another Down syndrome baby) and prenatal diagnosis if want to terminate

Question 37

what is a balanced chromosomal abnormality

Answer 37

where no genetic info is lost even if DNA is lost. no phenotypic changes

Question 38

what is unbalanced chromosomal abnormality

Answer 38

individual is affected. phenotype is changed

Question 39

what is reciprocal translocation

Answer 39

when 1 part of chromosome breaks off and joins another

Question 40

problem with reciprocal translation

Answer 40

often may not have any genetic info so is balanced but when new part of chromosome fuses with another may cause fusion of new gene resulting in an unbalanced chromosome

Question 41

how is a quadrivalent formed and what is the problem with this

Answer 41

when 2 sets of chromosomes undergo reciprocal translation and then are joined together creating a quadrivalent instead of a bivalent. can separate causing unbalanced chromosomes

Question 42

types of quadrivalent separation and which causes unbalanced and balanced chromosomes

Answer 42

alternate - alternate centromeres (opposites) (balanced)
adjacent 1 - non homologous centromeres (unbalanced)
adjacent 2 - homologous centromeres (unbalanced)
= problem if unbalanced

Question 43

what can robertsonian translocation cause

Answer 43

risk of aneuploidy. may cause trisomies, monogamies, normal or a balanced carrier after meiosis. look at diagram at end of slide