Exam 4 - Ch. 15

Question 1

What is the C-value?

Answer 1

the total amount of DNA found in a cell

Question 2

What are the two types of Prokaryotes?

Answer 2

bacteria and archaea

Question 3

What is the C-value paradox?

Answer 3

In eukaryotes, where there is little correlation between DNA quantity and an organism’s perceived morphological complexity

Question 4

What are the two phenomena that explain the C-value paradox?

Answer 4

1. whole-genome duplications resulting in polyploidy (genome is doubled)
2. the existence of large portions of an organism’s genome that are largely functionless from the cell’s viewpoint

Question 5

What does Satellite DNA do?

Answer 5

the tandemly repeating sequences of DNA that are commonly used for DNA profiling

Question 6

What do telomeres do?

Answer 6

they are the regions of repetitve DNA at the end of the chromosome, that protect against chromosomal deterioration

Question 7

What do introns do?

Answer 7

they are the non-coding sequences within genes that are removed by RNA splicing

Question 8

What do Non-coding RNA genes do?

Answer 8

they are the codes for RNA molecules that are not translated into proteins

Question 9

What are gene regulatory sequences?

Answer 9

sequences involved in the process of transcription (ex: promoters, enhancers, and silencers)

Question 10

Larger genomes have:

Answer 10

more DNA that codes for proteins

Question 11

The size of a plant or animal’s genome is unrelated to its body size or phylogenetic position. True or false?

Answer 11

True

Question 12

In complex organisms, RNA molecules transcribed from __________ regions of the genome have roles in regulating gene expression, so in other words, they do not code for _________.

Answer 12

noncoding regions, proteins

Question 13

What do mobile genetics elements do, and how do they do that?

Answer 13

replicate and insert themselves into an organism’s genome regardless to the consequences to the organism, by hijacking the same cellular machinery that replicates and transcribes protein-coding DNA

Question 14

What are mobile genetic elements sometimes called and why?

Answer 14

selfish genetic elements, because they are more focused on making copies of themselves

Question 15

Mobile genetics elements can:

Answer 15

1. can cause gene duplication elements
2. can cause mutations in protein-coding regions, which alters the protein functions
3. can rearrange genes in the host genome

Question 16

Mobile genetic elements can disrupt the function of? What does this result in?

Answer 16

protein-coding genes, results in obvious changes to an organism’s phenotype

Question 17

How much of the DNA sequence is derived from mobile genetic elements?

Answer 17

45%

Question 18

Do unicellular organisms have mobile genetic elements in their genomes?

Answer 18

they often do not

Question 19

Intergenic regions

Answer 19

space between coding genes in the eukaryotic genome

Question 20

What makes up the intergenic regions?

Answer 20

mobile genetic elements and their remnants

Question 21

What is the most predominant noncoding DNA found in eukaryotic genomes?

Answer 21

introns

Question 22

Where do introns occur?

Answer 22

within the coding regions of genes

Question 23

What are introns transcribed into?

Answer 23

mRNA

Question 24

Unicellular eukaryotes typically have _ to _ introns per genome.

Answer 24

1 to 2

Question 25

What is the average amount of introns in vertebrates?

Answer 25

5-8

Question 26

Do prokaryotes have introns?

Answer 26

no

Question 27

Is there any implied importance to the positions of introns?

Answer 27

yes

Question 28

Just because MGEs could be considered parasitic, does this mean they are good or bad?

Answer 28

neither

Question 29

Could mobile genetic elements be considered parasitic?

Answer 29

yes

Question 30

Transposons

Answer 30

mobile genetic elements that can change their position within a genome

Question 31

Retrotransposons

Answer 31

mobile genetic elements that leave a copy of themselves behind when they move

Question 32

How do retrotransposons leave copies of themselves behind?

Answer 32

by converting RNA into DNA through reverse transcription

Question 33

What happens if transposition occurs in the germ line?

Answer 33

it will be passed on to the host's offspring

Question 34

Do host genomes have mechanisms to counter mobile genetic elements?

Answer 34

yes

Question 35

What are the mechanisms used to defend against mobile genetic elements?

Answer 35

DNA methylation and RNA silencing

Question 36

Methylation

Answer 36

attachment of methyl groups to nucleotides, which prevents the transcription of DNA into RNA, thus preventing retrotransposons

Question 37

RNA interference/RNA silencing

Answer 37

short sequences of RNA that match a particular mobile genetic element, and silences the expression of it

Question 38

Polyploidization

Answer 38

whole-genome duplication

Question 39

Segmental duplication

Answer 39

duplication that affects smaller sections of the genome, can copy a single complete gene, a piece of a gene, or several genes

Question 40

What are the molecular mechanisms that cause segmental duplication?

Answer 40

unequal cross-over between chromosomes during meiosis, and mobile genetic elements

Question 41

Duplication events are often selectively _______. Why?

Answer 41

neutral, because it does not affect the phenotype

Question 42

Does fixation typically occur by chance alone? What does this mean for duplications in the long run?

Answer 42

- No, neutral alleles rarely drift to fixation - most duplications are soon lost from a population

Question 43

What are the steps taken to preserve duplicated genes?

Answer 43

1. a duplicated allele must rise to fixation in a population 2. one of those duplicates acquires a mutation that changes its function from A to B 3. one of the gene copies acquires a mutation that changes its function 4. the new allele contains one copy that performs the new function, and then a second copy that performs a new function

Question 44

What is the reason for the preservation of a duplicated gene?

Answer 44

can be attributed to selection, the new function increases fitness

Question 45

Neofunctionalization

Answer 45

the gene copy that mutates from the original acquires an entirely new function that by chance benefits the organism

Question 46

What happens to each copy of a gene in neofunctionalization?

Answer 46

one copy continues to perform the ancestral function, while the other acquires mutations that give it a new function

Question 47

What is the widely accepted mechanism for the preservation of duplicate genes?

Answer 47

neofunctionalization

Question 48

Subfunctionalization

Answer 48

the ancestral gene has two different functions, meaning that after the ancestral two-function gene is duplicated, one copy performs the ancestral function A, while acquiring a mutation that inhibits the other ancestral function

Question 49

What eventually happens to a gene in subfunctionalization?

Answer 49

The other copy acquires another mutation that inhibits the ancestral function B

Question 50

Gene families

Answer 50

groups of anywhere from two to hundreds of genes that are all descendants of a single ancestor gene

Question 51

What are gene families a result of?

Answer 51

repeated duplication events

Question 52

All genes in a gene family typically have similar structures and functions, but they do not:

Answer 52

perform identical function

Question 53

What was adaptive genetic variation generated by?

Answer 53

mutational processes

Question 54

Adaptation from new mutation

Answer 54

if the alleles that encode a novel adaptive phenotype appear after a new selective challenge arises (selection causes a new mutation)

Question 55

Adaptation from standing genetic variation

Answer 55

alleles favored by the new selective challenge are present at low frequency in the population before the challenge arose (mutation was neutral until selected for)

Question 56

What is the neurotoxin that garter snakes possess?

Answer 56

tetrodotoxin, which block the movement of sodium ions across cell membranes, and result in paralysis

Question 57

What is theory behind garter snakes being resistant to neurotoxin tetrodotoxin?

Answer 57

it is possible that the alleles conferring with the resistance were passed down from the common ancestor

Question 58

How did the resistance for TTX arise in each species?

Answer 58

independently

Question 59

What is the adaptive resistance to TTX in garter snakes an example of?

Answer 59

adaptation from new mutation