d1.3 mutations and gene editing

what is a gene mutation?

a random change in the base sequence of a gene

what is a substitution mutation?

one base is replaced by another

what is the effect of a substitution mutation?

a single base change

what is an insertion mutation?

an extra base is added into the sequence

what is the effect of an insertion mutation?

a nucleotide is added and can shift the reading frame 

what is a deletion mutation

a base is removed from the sequence

what is the effect of a deletion mutation

removes nucleotide and can shift reading frame

what are base substitutions?

when one nucleotide in DNA is replaced by another

What is a single-nucleotide polymorphism? (SNP)

When a base substitutions is inherited 

• increase genetic diversity but may or may not affect protein function

what are the mutations of a base substitution?

Same-sense (silent), Mis-sense, and nonsense

what is a same-sense/silent mutation’s effect on protein

codon changes but codes fro the same amino acid b/c of code degeneracy

what is  a mis-sense mutation’s effect on protein?

codon changes and codes for a different amino acids 

what is the possible outcome of a mis-sense mutation?

can alter protein function

what is the effect of a nonsense mutation on protein?

a codon changes to a stop codon 

what is the possible outcome of a nonsense mutation?

early termination or incomplete/nonfunctional protein

what is a frame shift mutation?

• the reading frame of codons is shifted during translation due to insertion/deletion of 1 or 2 nucleotides 

what is the effect of a frame shift mutation?

every amino acid is changed after the mutation, usually causes a nonfunctional protein

what is the effect of the insertion/deletion of multiple of 3 nucleotides?

reading frame is not shifted but adds/removes whole amino acids

• can cause major structural changes and affect protein function

what is the effect of a major insertion/deletion on a polypeptide?

usually the polypeptide loses function completely due to large disruption in protein structure/sequence

when does mutation rate increase?

during DNA replication because of base-pairing errors that may not get fixed

what are mutagens?

external factors that increase mutation rates 

what is a radiation mutagen?

high energy radiation causes chemical changes in DNA

what are chemical mutagens?

chemicals that chemically alter DNA bases or cause breaks

where do mutations occur?

anywhere in the genome

where do mutations in germ cells occur?

cells that produce gametes (sperm and eggs)

• can be passed on to offspring as new alleles

what can mutations in germ cells do?

• rarely provide a beneficial trait

• cause genetic diseases

where do mutations in somatic cells occur?

occur in body cells other than gametes

• not inherited by offspring

what are the effects of a mutation in somatic cells?

• affects only individual cells and can not be inherited by offspring 

• have limited effects

• can cause cancer if mutations affect proto-oncogenes, which control cell division 

what are alleles?

different version of a gene

how does mutation create genetic variation?

• mutation creates new alleles by altering existing ones

what increases genetic variation?

• mutations that make new alleles 

• meiosis and sexual reproduction (mixing alleles) 

what are examples of chemical mutagens?

carcinogenic, mustard gas

what are examples of mutagenic forms of radiation?

UV rays, gamma rays, → melanomas

what is gene knockout?

technique used to study the function of a gene by making it nonfunctional

how does gene knockout work?

• gene is replaced/displaced in the genome

• results with organism lacking a working copy of that gene called the knockout organisms

• by observing the changes/phenotype researchers can infer the gene’s role

why is gene knockout important

• identify gene functions when unknown

• helps studying genetic diseases

what is cripsr-cas9?

stands for clustered regularly interspaced short palindromic repeats

• natural system found in

how does CRISPR work?

• guide RNA (gRNA) directs Cas9 to target DNA

• Cas9 makes a two strand break at the target site

• allows scientists to edit genes by cutting and replacing DNA sequences

how does Cas9 locate target DNA?

Cas9 moves along DNA to find the sequence complementary to gRNA

how does DNA repair and editing work with CRISPR?

Cell repairs the break created by Cas9, allowing for insertion, deletion, or replacement of DNA sequences

what are conserved sequences?

DNA sequences that are identical or very similar across species or groups of species

• highly conserved sequences remain unchanged or very similar over long evolutionary times

where are conserved sequences found?

• protein coding genees

• regions that make rRNA or tRNA

• sequences that regulate gene expression

what are conserved non-coding elements?

conserved DNA regions that do not code for proteins

what are germ cells/ gametes

cells that are passed off to offspring

• sex cells