L 11: Hereditary Effects of radiation

Question 1

Radiation sterility

BOard question! for sure

Answer 1

• As you can see in the table, spermatogonia give rise to spermatozoa. Spermatogonia are destroyed by RT. Spermatozoa are still around till its life span. so there is a laten period before sterility in men due to this delay.
• Females no latent period or temp sterility as all the oocytes are there from day 3 of life.

Question 2

Dose rate sensitive organ

Answer 2

Testis
Since it is dose dependent we always treat testicular cancer with single dose than fractionated dose.

Question 3

Male germ cell sterility

Answer 3

• temp. sterility in single dose = 0.15 Gy
• temp. sterility in prolonged dose rate = 0.4Gy /y
• permanent sterility = 3.5 – 6 Gy, annual dose of 2Gy/y

Question 4

Female germ cell sterility

Answer 4

• Permanent sterility = 2.5 – 6 Gy, annual dose of 0.2 Gy/y
• Oocytes are equally sensitive throughout life

Question 5

LET and mutations

Answer 5

• High LET = large mutations
• Low LET = small deletions

Question 6

Dose for double mutation rates

Board question

Answer 6

1Gy

Question 7

Risk assessment for developing mutations

Answer 7

1. Most mutations induced by radiation are harmful–questionable
2. Any dose of radiation entails some genetic risk
3. # mutations is proportional to dose
4. Risk estimates for mouse then extrapolation to human seem appropriate

Question 8

ICRP total population heritable effects

Answer 8

0.2% per Sv

Question 9

ICRP working population heritable effects

Answer 9

0.1% per Sv

Question 10

Epigenetics

Answer 10

• Study of changes in gene expression of cellular phenotype caused by mechanisms other changes other than underlying DNA sequences
• Eg: due to methylation, cell differentiation, imprinting

Question 11

X-Chromosome inactivation

Answer 11

Soon after female embryonic stem cells start to differentiate, the two X chromosomes (purple) come together in the nucleus, and the X-inactivation centres, which initiate X-chromosome inactivation, interact. These events occur concomitantly with the process of X-chromosome counting and choice and lead to upregulation of Xist transcription (red) from the future inactive X chromosome (Xinactive).

Question 12

Summary

Answer 12

• There is no signature lesion or mutation that is specific for ionizing radiation.
• Exposures at low dose rates give lower mutation rates than the same dose given at a high dose rate.
• Radiation tends to affect the same mutations that are induced spontaneously.
• The number of mutations is proportional to the dose of radiation.