L10. Gene & genome evolution

Question 1

explain how genes are altered

Answer 1

• exon shuffling
• transposition
• horizontal gene transfer

Question 2

alteration of genes - exon shuffling

Answer 2

• two or more genes can be broken and rejoined, creating a hybrid gene
• often occurs on intron sequences which do not encode protein

Question 3

alteration of genes: exon shuffling - does it have to precise, why or why not?

Answer 3

• no
• bc the intron sequences are removed by RNA splicing

Question 4

alteration of genes - transposition

Answer 4

• mobile genetic elements move from one chromosome location to another
• can alter the activity or regulation of a gene

Question 5

gene alteration - horizontal gene transfer

Answer 5

• a piece of DNA can be transferred from the genome of one cell to another
• rare in eukaryotes but common in bacteria

Question 6

gene alteration: horizontal gene transfer - bacterial conjugation

Answer 6

• begins as the donor cell attaches to a recipient cell using a sex pilus
• the sex pilus facilitates the transfer of genetic material

Question 7

what are the consequences of mutations in regulatory DNA

Answer 7

• 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

Question 8

consequences of mutations in regulatory DNA - lactose intolerance

Answer 8

• 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

Question 9

explain a mechanism of gene duplication

Answer 9

• unequal crossing over
• results in one chromosome getting two copies of the gene and the other getting none

Question 10

outcomes of gene duplication

Answer 10

• goblin gene family
• repeated rounds of duplication and mutation are thought to have generated them

Question 11

explain the 2R hypothesis of whole genome duplication

Answer 11

• 1st round of genome duplication resulted in emergence of vertebrates
• 2nd round of genome duplication gave rise to jawed vertebrates

Question 12

what is exon shuffling

Answer 12

• when exons from one gene is added to another
• this then facilitates the evolution of new proteins

Question 13

what are germ-line cells

Answer 13

• they propagate genetic information into the next generation
• includes reproductive cells (eggs and sperm)

Question 14

what are somatic cells

Answer 14

• they are all the cells in the body that are not reproductive cells
• do not contribute their DNA to the next generation

Question 15

what is the consequence of a mutation in a germ-line cell

Answer 15

it will be passed on to the cells progeny and to the progeny of the organism

Question 16

what is the consequence of a mutation in a somatic cell

Answer 16

it will affect only the progeny of that cell and will not be passed on to the organism’s progeny

Question 17

how can you experimentally measure mutation rates

Answer 17

• 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

Question 18

explain how mutations impact divergent evolution

Answer 18

• accumulated mutation can result in two species diverging
• the coding sequence of the exon will be more conserved than the intron sequence

Question 19

what are transposons

Answer 19

• 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

Question 20

transposons - bacteria vs humans

Answer 20

• bacteria: many ‘DNA only’ transposons
• humans: has two families of transposable sequences

Question 21

transposons - human transposons

Answer 21

• cut-and-paste transposition
• replicative transposition
• retrotransposons

Question 22

transposons - cut-and-paste transposition

Answer 22

• 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

Question 23

transposons - replicative transpoition

Answer 23

• the element is copied by DNA replication
• the donor is unchanged but the target molecule receives a copy of the element

Question 24

transposon - retrotransposon

Answer 24

• 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

Question 25

what are three sources of variation in genomes

Answer 25

• single-nucleotide polymorphisms (SNPs)
• copy-number variations (CNVs)
• other repeat sequence prone to mutations

Question 26

genome variability - single nucleotide polymorphisms

Answer 26

• inherited
• points in the genome that differ by a single nucleotide pair between one portion of the population and another

Question 27

genome variability - copy-number variations (CNVs)

Answer 27

• inherited
• duplication and deletion of large segments of DNA
• genes conferring susceptibility to diseases

Question 28

genome variability - other repeat sequences

Answer 28

• short tandem repeats can vary widely between individuals and can increase from one generation to the next
• ex: CACA repeats are often replicated inaccurately

Question 29

how do viruses reproduce?

Answer 29

• 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

Question 30

how do retroviruses reproduce

Answer 30

• 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