Skip to content
MathsGenie logo
Open app

Course home

  1. A Level
  2. Biology AQA
  3. Question bank

Gene expression is controlled by a number of features (A-level only)

EasyMediumHard
12
Question 1

Demyelination of axons in the peripheral nervous system leads to a loss of nerve conduction velocity. Scientists investigated whether transplanting neural crest stem cells could help repair demyelinated sciatic nerves in rats.

They divided rats with induced sciatic nerve demyelination into three groups:

  • Control group: received a sham injection containing no stem cells.
  • TF-4+TF\text{-}4^+TF-4+ group: received a transplant of stem cells containing a fully functioning TF-4TF\text{-}4TF-4 gene, which codes for a transcription factor that stimulates the transcription of myelin-associated genes.
  • TF-4−TF\text{-}4^-TF-4− group: received a transplant of stem cells lacking a functional TF-4TF\text{-}4TF-4 gene.

After 14 days, the scientists measured the mean nerve conduction velocity of each group. The results are shown in the table below:

GroupMean nerve conduction velocity (m s−1\text{m s}^{-1}m s−1)
Control2.42.42.4
TF-4+TF\text{-}4^+TF-4+8.48.48.4
TF-4−TF\text{-}4^-TF-4−4.84.84.8

Fourteen days after transplantation, histological analysis showed that in the TF-4+TF\text{-}4^+TF-4+ group, 65%65\%65% of the damaged nerve fibers were newly myelinated. The control group had no newly myelinated fibers.

Assuming that the increase in mean nerve conduction velocity above the control baseline is directly proportional to the percentage of damaged nerve fibers that are newly myelinated, calculate the percentage of damaged nerve fibers that are newly myelinated in the TF-4−TF\text{-}4^-TF-4− group.

[2]

Gene expression is controlled by a number of features (A-level only) Questions

  1. A Level
  2. /Biology
  3. /Gene expression is controlled by a number of features (A-level only)