RADIOBIOLOGY AND RP CD # 4 GENETIC EFFECTS
REVISED OCT 2006
PG1
#1 Geneitc effects of radiation and DNA - all radiation damage starts with a
single photon – different chains of events can occur
Usually results in insignficant damage to a water molecule or cell
Ocassionally biologic damage that results in genetic effects can occur
#9 When DNA is damage – can result in cell death. One cell is not a problem –
that many cells affected in a small area - when this happens , tissue or organs
can be damaged or distroyed.
# 10
The importance of DNA as a storehouse of genetic information –
Each cell has a nucleus where DNA with other molecules form chromosomes.
The chormosomes control growthand development of cells and orgarns –
affecting ghe characteristics of a person. Changes in the genetic code can alter
the cell’s growth and function
Dna – Chromosome – Cell – Tissue – Organs – Human
16 – CELL DIFFERIATION – ALL CELLS CONTAIN GENES – WHICH GENES
ARE TURNED ON DETERMINES WHAT TYPE OF CELL IT WILL DEVELOP
INTO
Why are there defferent kinds of cells? What causes a cell to develop into a
muscle or bone cell? The function is determined by which genes are TURNED
ON in each cell (the same instruction book – but different pages)
17 – GENES STORED IN CHROMOSOMES
Humans have 46 chromosomes in 23 pairs –each pair has a maternal and
parternal chromosome - when they combind in a daughter cell – there are over
16 million possible combinations
19 – Each person inherits half of their genes from mother and father.
Dominant will be expressed over recessive
GENERAL PRINCIPLES OF GENETIC INHERITANCE
DOMINANT gene + DOMINANT gene = DOMINANT EXPRESSION
DOMINANT gene + RECESSIVE gene = DOMINANT EXPRESSION
RECESSIVE gene + RECESSIVE gene = RECESSIVE EXPRESSION
(but not all genes are completely dominant – so sometime the recessive can
sneak through)
Example eye color:
Blue eyes recessive
Brown eyes - dominant
20 - Sex Linked Genes –
RADIOBIOLOGY AND RP CD # 4 GENETIC EFFECTS
REVISED OCT 2006
PG2
Males have only one X chromosome – so some mutations can expressed without
having the complementary gene – these will appear in the first generation of
males - Common sex linked gene is color blindness and hemophilia
Since females have 2 X – they always require a matching – so females can pass
on the disorder without expressing it.
24 – Common Gene Mutations
25 – MOST RADIATION-INDUCED GENETIC MUTATIONS ARE RECESSSIVE
– THEREFORE ARE NOT EXPRESSED (SEEN) FOR GENERATIONS
Radiation is thought primarily to cause recessive mutations – so if any form of
genetic mutation does occur due to low doses of radiation. the chance of actually
expressing it is very low
Both parents must have the mutated recessive gene to pass it on
32- Chromosome have been damaged – when recombined they are missing
significant genetic material – that will eventually cause cell death
42 –
RISK ESTIMATES – based on probabilities of large populations
MALE MORE LIKELY THAN FEMALE TO TRANSMIT GENETIC MUTATION–
SOON AFTER RADIAITON (SPERM LIFE)
HIGHEST RISK – MALE SPERM THAT FERTILIZE OVUM WITHIN SEVERAL
MONTHS OF IRRADIATION
Reduce the risk of passing on mutations by postponing conception of a child until
the risk is minimized
43 LIFE SPAN SHORTENING CHART
Radiography is a safe occuapation!
RISK
RISK OF DECREASING LIFE SPAN
EXPECTED DAYS LOST
Being MALE
Heart Disease
Smoking (1pk/day)
Accidents
Occupational Accidents
Radiation Workers
2800
2100
1600 (4.3 years)
435
74
12 ( 1 day per Rad ?)
RADIOBIOLOGY AND RP CD # 4 GENETIC EFFECTS
REVISED OCT 2006
PG3
46 conclusions
1. Different mutations have different radiosensitivities
2. Same dose given over a longer period of time = less mutations
3. Males are more sensitive to radiation than females
4. Germ cells (sperm & ovum)are at risk at all doses of radiation
5. Most radiation induced mutations are recessive
6. Radiation induced mutations are very rare
47 NO SIGNIFICANT GENETIC MUTATIONS SEEN WITH A BOMB
SURVIVORS
Although studies indicate a clear connection between radiation and genetic
mutations.
Therefore is was assumed that children born to A-bomb survivors in Japan would
also show genetic mutations.
In Fact – this has not been the case.
Studies of 3 generations of survivors have not shown any increase in genetic
mutations – when these children were compared to other Japanese children.
The lack of genetic mutations resulting form the Atomic bomb does not mean
that genetic mutations did not occur – there were some trends to indicate a
possible increase in certain genetic mutations.
Radiation-induced genetic mutations are unique and are extremely rare.
# 48 MALES MORE SENSITIVE THAN THE FEMALES
MORE EXTERNAL GONADS – MORE LIKELY TO ABSORB RADIATION
In males, sperm is continually being reproduced from stem cells – this stage is
the most radiosensitive and any damage at this time can be passed along to the
sperm that develop
In Females – the follicle is the most radiosensitive stage, but there is also more
time for repair before producing ova
# 49
25 – 50 RAD DOSE CAN CAUSE GENETIC MUTATIONS
Advisable to wait several months to conceive if dose is above 10 rad for female
Males are advised to wait several month to procreate– GET RID OF DAMAGED
SPERM
APPROXIMATE DOSE:
BE = 8 RAD FOR FEMALES
HIP = 3.7 RAD FOR MALES