Manipulating genomes

Question 1

Explain how the automated sequencing machine orders the DNA fragments from the PCR

Answer 1

electrophoresis ;
(negatively-charged DNA) moves towards ,
positive electrode / anode ;
smallest/smaller (fragments) move, fastest / faster ; ora
resolution on gel sufficient to register 1, nucleotide /
base;

Question 2

It is proposed that a simple saliva test could identify those children who have the mutation.
What would be the source of the genetic material used in this test?

Answer 2

(epithelial) cells lining cheek

Question 3

Name the enzyme that can be used to convert mRNA to single-stranded DNA.

Answer 3

reverse transcriptase

Question 4

Explain how the locations of the fluorescent spots on the DNA chip reveal which genes are most active.

Answer 4

1 mRNA binds to , (gene) probes / cDNA / ssDNA ,
by complementary base pairing ;
2 idea that the more active the gene
the more mRNA produced ;
3 during transcription ;
4 more fluorescence indicates more mRNA (bound) ;

Question 5

Outline the roles of each of the following procedures in sequencing a genome:
the polymerase chain reaction (PCR)

Answer 5

to, amplify / make (many) copies of, DNA ;

(range of) different lengths ;

Question 6

Outline the roles of each of the following procedures in sequencing a genome:
electrophoresis

Answer 6

to put DNA pieces in size order ;

to read, base sequence / order of bases ;

Question 7

Outline the roles of each of the following procedures in sequencing a genome:
restriction enzymes

Answer 7

to cut (genome DNA) into, small(er) / 750 bp, fragments ;
to cut, vectors / BACs / plasmids, (for gene library) ;

Question 8

Suggest why a genome has to be fragmented before sequencing.

Answer 8

genome, too big / very large ;
accuracy better / fewer errors (with small fragments) ;
divide job over, time / different labs ;

Question 9

Explain why injecting recombinant HGH in this way is not an example of gene therapy.

Answer 9

1 (child’s) cells / DNA / genes / alleles ,
not changed ;
2 vector not used (in child) ;
3 child / cells , not producing , HGH / hormone ;
4 HGH / drug / injection ,
has to be given repeatedly /
is a short term solution / not a cure ;

Question 10

Name the process that:
has given rise to the modern domestic cat from its wild ancestor
has given rise to coat colour variation in cats.

Answer 10

selective breeding / artificial selection ;
(named type of) mutation / production of new alleles ;
sexual reproduction / meiosis / independent assortment /
crossing-over ;

Question 11

Suggest why physiological problems are more common in pedigree animals.

Answer 11

1 inbreeding / small or decreasing, gene pool ;
2 homozygous recessive (genotypes) ;
3 gene / allele , for desired characteristic on same
chromosome as problem, gene / allele ;
4 selecting for one trait (unintentionally) selects for another ;
5 breeders select for looks not health ;
6 weaker selection against less healthy animals (than in wild) ;

Question 12

Define the term recombinant DNA.

Answer 12

DNA (combined) from (two) , sources / organisms ;

Question 13

Suggest why the Hardy-Weinberg principle cannot be used to predict the expected frequencies of albino and non-albino alleles in the worldwide zoo population of tigers.

Answer 13

population, not large / (too) small ;

not randomly-mating / matings arranged ;

Question 14

List two factors that might cause allele frequencies to change from generation to generation in a population that meets the Hardy-Weinberg criteria.

Answer 14

natural / artificial / directional, selection ;
genetic drift ;
mutation ;
migration / AW ;

Question 15

Discuss the potential benefits to mankind and the ethical concerns raised by the following examples of genetically modified organisms:
• rice modified for increased vitamin A content (‘Golden Rice™’)
• humans having somatic gene therapy treatment for a genetic disease.
In your answer you should give a balanced account of the benefits and concerns for each example of genetic modification.

Answer 15

‘Golden RiceTM‘
B1 reduce vitamin (A) deficiency in named area / ora ;
B2 reduce, eye problems / blindness ;
C1 reduce rice genetic, diversity / variation ;
C2 clone may suffer from one, disease / environmental change ;
C3 hybridisation with wild rice / spread genes to wild populations ;
C4 seeds expensive / need to be bought each year ;
C5 rice may not grow in all areas where needed ;
C6 idea of doubts whether vitamin A content sufficient ; 4 max
Somatic Gene Therapy
B3 cure / reduce symptoms / better quality of life / less medication;
B4 cystic fibrosis / SCID / Parkinson’s / thalassaemia / LCA ;
B5 extend lifespan / saves lives ;
C7 virus vector may cause (viral) disease ;
C8 procedure may be, invasive / dangerous / painful / stressful ;
C9 temporary / needs to be repeated / limited success ;
C10 immune system / rejection, problems ;
C11 animal testing concerns ; 4 max
Either Section
C12 antibiotic resistance gene transfer to pathogenic bacteria ;
C13 unknown effects / cause mutation ;

Question 16

State the name given to the process in which only a certain percentage of adult foxes were chosen by humans to breed in each generation.

Answer 16

artificial selection / selective breeding ;

Question 17

Suggest why 20% of the female foxes were used for breeding but only 5% of the male foxes.

Answer 17

idea that males can father many offspring / mate several females ;
idea that females produce only a few offspring ;
(so) more females (than males) needed to
maintain numbers (each generation) ;
(20% females chosen as) inbreeding / genetic problems,
if breeding population is too small ;
(5% males chosen as) selection pressure stronger
if fewer (tamest) are used ;

Question 18

suggest about the causes of the variation in tameness behaviour in silver foxes.

Answer 18

1 (mostly) genetic ;
2 as can be selected for / selective breeding increases frequency ;
3 allele(s) for tameness ;
4 (from) mutation ;
5 query role of environment / learning ;
6 ref. DRD4 / dopamine receptor ;

Question 19

use the below to explain why some traits became more common in tame foxes.

linkage

epistasis

inbreeding

genetic drift

Answer 19

linkage
tameness genes and genes for these traits on same
chromosome ;
(so) inherited together ;
epistasis
(product of) one gene affects expression of another ;
via enzyme pathway ;
inbreeding
(hidden / masked) recessive alleles ;
selected for, as well / unintentionally ;
more chance homozygous as, small gene pool / parents related ;
genetic drift
random / chance (which alleles, present / passed on) ;
(effect stronger because) small breeding population ;

Question 20

Why is the continued existence of rare breeds of farm animals desirable?

Answer 20

1 genetic resource / gene bank / have (different) alleles ;
2 for , genetic engineering / genetic modification /
artificial selection / selective breeding / described ;
3 if conditions change / in the future ;
4 example of useful trait ;
5 to maintain , biodiversity / genetic diversity /
(large) gene pool

Question 21

Describe the differences between:

somatic cell gene therapy and germ line cell gene therapy

Answer 21

somatic
changes / uses , body cells ;
change cannot be passed to offspring ;
cures / alleviates , genetic disease in one individual ;
short-lived / repeat treatments needed ;
germ line
changes / uses , gametes / zygote / embryo /
 reproductive tissue ;
banned ;

Question 22

Explain why there was such a rapid loss of elm trees in Britain as a result of this elm disease.

Answer 22

1 genetically identical / little genetic variation ;
2 all susceptible / none resistant , to this disease ;
3 beetles , move / fly , from tree to tree
or beetles are vector ;
4 trees grow , in clonal patch / close together
or disease spreads through , suckers / roots
or connected by , suckers / roots ;
5 the beetles only , live on / target , elm trees ;
6 attempts at control contributed to spread ;
7 as more trees became diseased then
more tree surgery was necessary
(contributing to spread of problem) ;
8 as more trees became infected then
more , saws / equipment , were contaminated ;

Question 23

State three phenotypic traits (characteristics) that have been selected for in dairy cows.

Answer 23

1. idea that (produces)
   large , yield / volume / amount, of milk ;
2. idea of long lactation period ;
3. idea of high milk quality ;
4. large udders /
   correct udder shape (for milking machine) ;
5. resistance to , (named) disease / mastitis / pathogens
   or
   effective immune system ;
   6.idea of calm temperament ;

Question 24

Suggest why monkeys rather than other laboratory animals, such as rats, were used for this work and comment on whether their use in this way is justified or not.

Answer 24

monkeys rather than rats:
1. idea that (humans & monkeys) closely related /
share more genes / share a common ancestor ;
2. (humans & monkeys) both primates ;
3. idea that brain / body ,
structure / physiology / behaviour ,
similar (to humans) ;
4. monkey brain bigger (than rat) ;

Question 25

Suggest two characteristics that researchers should look for when choosing an organism for research into how genes control development.

Answer 25

1. small ;
2. short life cycle ;
3. easy to, keep / breed / AW ;
4. cheap (to buy / keep ) ;
5. readily available / common / not rare ;
6. large cells ;
7. previously well-studied / many known mutants ;