forensics

Question 1

explain the role of DNA primers in the production of the amplified sequence

Answer 1

primers have a specific base sequence
bind to complementary bases of the DNA to be amplified
therefore provide a site for the DNA polymerase to bind

Question 2

explain why amplified DNA fragments of alleles are different

Answer 2

the base sequences of the alleles
the restriction enzyme cuts at a specific site/ DNA base sequence which is only present in one of the alleles
therefore a shorter fragment is produced for one allele

Question 3

devise an investigation to determine the optimum number of cycles for the polymerase chain reaction used to amplify the DNA for the test

Answer 3

provide DNA and polymerase primers
control temperature- 95,55 and 70 for cycle
change number of cycles
use gel electrophoresis to determine quantity of DNA produced
choose smallest number of cycles that produces an observable band

Question 4

Body farms use the bodies of pigs to study the changes in insect species on a body after
death.
Describe how this study could be carried out.

Answer 4

standardise size and breed of pigs studied
control temperature after death
record the presence of different species of insects
at regular time intervals

Question 5

Explain how the results of this study ( of pigs) could be used to help to establish the time of death
of a human

Answer 5

record which species are present on the human
compare with results of investigation of pigs
account for stage of life cycle are present
environmental variables may need to be taken into account if using stages of succession

Question 6

Describe how DNA profiling could be carried out to show that these snakes are different
species.

Answer 6

obtain DNA from two types of grass snake
PCR/ restriction enzymes used to produce fragments of DNA
gel electrophoresis used to analyse DNA samples by separating fragments of dna
more differences in pattern of bands indicates the snakes are different species

Question 7

describe the changes that occur inside a body in the first week after death

Answer 7

body temperature falls
rigor mortis
autolysis/ break down of cells by enzymes in the body
discolouration/ bloating

Question 8

Describe the role of decomposers, such as microorganisms, in the carbon cycle

Answer 8

decomposers break down organic material from the dead body
decomposers respire
releasing co2 into atmosphere

Question 9

Explain the effect of temperature on the rate of growth of blowfly maggot

Answer 9

temperature affects enzymes/ metabolism
increase in temp increases kinetic energy
producing more frequent collisions between enzyme and substrate molecules

Question 10

how is dna amplified

Answer 10

polymerase chain reaction

Question 11

Devise a procedure, using electrophoresis, to compare the amplified DNA from these two
types of human.

Answer 11

restriction enzymes used to cut DNA from both samples into fragments
DNA sample loaded onto agarose gel
electric current passed through the gel
markers are added to visualise the bands/ gene probe/ DNA strain
position of bands produced can be compared

Question 12

Explain the effect of ambient temperature on the rate of decomposition

Answer 12

increase in temp will increase rate of decomposition
- increases enzyme activity
- increases growth rate of bacteria/ decomposers

Question 13

Explain how microorganisms in the soil break down the stems.

Answer 13

stems contain starch or cellulose
enzymes secreted by microorganisms which break down glycosidic bonds
releases glucose that is used by the microorganisms in respiration

Question 14

Describe how one PCR cycle would increase the quantity of DNA present

Answer 14

heat to 90-98 degrees to break down hydrogen bonds between DNA strand
annealing at 50-75
addition of nucleoltides
dna polymerase involved in formation of phosphodiester bonds
doubles quantity of DNA