L10. Gene & genome evolution Flashcards
explain how genes are altered
- exon shuffling
- transposition
- horizontal gene transfer
alteration of genes - exon shuffling
- two or more genes can be broken and rejoined, creating a hybrid gene
- often occurs on intron sequences which do not encode protein
alteration of genes: exon shuffling - does it have to precise, why or why not?
- no
- bc the intron sequences are removed by RNA splicing
alteration of genes - transposition
- mobile genetic elements move from one chromosome location to another
- can alter the activity or regulation of a gene
gene alteration - horizontal gene transfer
- a piece of DNA can be transferred from the genome of one cell to another
- rare in eukaryotes but common in bacteria
gene alteration: horizontal gene transfer - bacterial conjugation
- begins as the donor cell attaches to a recipient cell using a sex pilus
- the sex pilus facilitates the transfer of genetic material
what are the consequences of mutations in regulatory DNA
- during embryonic stage 1, organisms will express the same gene
- but the mutation will cause them to express different genes in stage 2
- this then has an effect on the organism’s development and appearance as an adult
consequences of mutations in regulatory DNA - lactose intolerance
- consequence of a point mutation in regulatory DNA
- the enzyme that breaks down lactose (lactase) is only expressed in infancy
- variant mutant genes continued to express lactase into adulthood
explain a mechanism of gene duplication
- unequal crossing over
- results in one chromosome getting two copies of the gene and the other getting none
outcomes of gene duplication
- goblin gene family
- repeated rounds of duplication and mutation are thought to have generated them
explain the 2R hypothesis of whole genome duplication
- 1st round of genome duplication resulted in emergence of vertebrates
- 2nd round of genome duplication gave rise to jawed vertebrates
what is exon shuffling
- when exons from one gene is added to another
- this then facilitates the evolution of new proteins
what are germ-line cells
- they propagate genetic information into the next generation
- includes reproductive cells (eggs and sperm)
what are somatic cells
- they are all the cells in the body that are not reproductive cells
- do not contribute their DNA to the next generation
what is the consequence of a mutation in a germ-line cell
it will be passed on to the cells progeny and to the progeny of the organism
what is the consequence of a mutation in a somatic cell
it will affect only the progeny of that cell and will not be passed on to the organism’s progeny
how can you experimentally measure mutation rates
- use bacterial cultures and expose them to a selective condition
- then you can find out which cells have a mutation that allows them to survive conditions that original cells could not
explain how mutations impact divergent evolution
- accumulated mutation can result in two species diverging
- the coding sequence of the exon will be more conserved than the intron sequence
what are transposons
- they are mobile genetic elements
- they are classified by mechanisms of movement of transposition
- they encode a specialized enzyme called a transposase that mediates their movement
transposons - bacteria vs humans
- bacteria: many ‘DNA only’ transposons
- humans: has two families of transposable sequences
transposons - human transposons
- cut-and-paste transposition
- replicative transposition
- retrotransposons
transposons - cut-and-paste transposition
- the element is cut out of the donor DNA and is inserted into the target DNA
- this leaves behind a broken donor DNA molecules that will be repaired
transposons - replicative transpoition
- the element is copied by DNA replication
- the donor is unchanged but the target molecule receives a copy of the element
transposon - retrotransposon
- the elements are first transcribed into an RNA intermediate
- next, a double-stranded DNA copy is synthesized by reverse transcriptase
- this DNA copy is then inserted into the target
- donor remains at its original location
what are three sources of variation in genomes
- single-nucleotide polymorphisms (SNPs)
- copy-number variations (CNVs)
- other repeat sequence prone to mutations
genome variability - single nucleotide polymorphisms
- inherited
- points in the genome that differ by a single nucleotide pair between one portion of the population and another
genome variability - copy-number variations (CNVs)
- inherited
- duplication and deletion of large segments of DNA
- genes conferring susceptibility to diseases
genome variability - other repeat sequences
- short tandem repeats can vary widely between individuals and can increase from one generation to the next
- ex: CACA repeats are often replicated inaccurately
how do viruses reproduce?
- the viral genome must enter a host cell and replicate to produce multiple copies
- these copies are transcribed and translated to produce the viral coat protein
- the genomes can then assemble spontaneously with the coat protein to form new virus particles
- the particles will then escape from the cell by lysing it
how do retroviruses reproduce
- they use reverse transcriptase to convert RNA to DNA
- next it will copy the viral DNA into RNA by the host cell RNA polymerase
- the viral RNAs then translate the host cell’s ribosomes to produce the retrovirus
