Seminar 1 2010 Question Page

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Understanding Gene Expression  

Seminar 1 2010

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SouthCity High School: Student BC - 25th April 2pm

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Understanding Gene Expression Question Page

This is where you post any questions you have before the seminar.

Jan Szydlowski - Onslow College 18.03 5:20pm

The loci (position) of a gene on a chromosome is important for proper expression. For example, some mutations result in pieces (or entire) chromosomes being cut and joined to other chromosomes resulting in new phenotypes. So how does the cell know where a gene is and when it needs to be turned on or off (ie expressed)?

Another question that has been buggin' me is from last years Level 3 Gene Expression exam question (three) about trisomy 21. Are the two karyotypes given correct (as I suspect) and if so why did they make an ammendment to change it? Interesting and challenging question though.

Michal Denny 19th March 2010

Hi Jan, Re your question about last year's Level 3 Gene Expression question (#3). Looking at it I'd say that while the two karyotypes are correct, the amendment was made to make the karyotype consistent with the heading. The heading says this person was a carrier, therefore they did not have Down Syndrome. The karyotype as printed is from a person with 3 copies of chromosome 21 (two at position 21 and one on top of chromosome 14), which means they had Down Syndrome.

Dr Deb Sloboda - 1 April 2010 Genes are turned on and off by proteins called transcription factors (TF) that bind to the promoter region of the gene. This is the region of the DNA that contains the instructions required for making the proteins that run the cell. Whether a particular gene is turned on (using TFs called activators) or off (using TF called repressors) is dependent upon which TF are contained within the cell, as every gene requires a unique set of transcription factors. Also, remember that we talked about another way to regulate genes, by changing the shape of the chromatin using DNA methylation - where methyl groups are attached to cytosine and turn it into 5-methylcytosine-methylated cytosine. Methylated DNA tends to be wrapped tightly around histone proteins and makes TF unable to bind to the promoter region and therefore prevents transcription.

Having identified the human genome some time ago - what percentage of this genome are they now aware of the gene and what it is controlling ? Pukekohe High School WT

Michal Denny 19th March 2010

Hi WT. Can you please clarify the second part of your question "are they now aware of the gene and what it is controlling" as I'm not quite sure what you are asking

Chandar Dewan - Tamaki College 24/03/10

1. is a marker/ biomarker just a precursor molecule that can be used to indicate the level of oxidative stress (because there is no way of measuring this directly??)

Questions from the Seminar

Emily Goh, Auckland Girls, 25 March 2010, 4.45pm

Can paramutation cause a change in gene expression?

Michal Denny 1st April 2010

The simple answer to this is yes.  Have a look at this article from the BBC for more explanation: Spotty mice flout genetics laws: (

Chandar Dewan - Tamaki College 

What’s the link between levels of progesterone in the mother and early onset of puberty?

Dr Deb Sloboda - 1 April 2010

None -the data that we presented was that the OFFSPRING of mothers fed a high fat diet had higher levels of progesterone later in life. These same offspring go into puberty early. The link between the two (high levels of progesterone and early puberty) is unclear. We have investigated whether or not the enzymes that are responsible for making progesterone were changed in the ovaries of these offspring but found no relationship. High progesterone levels are an indication of ovulation rates.

Student from Green Bay High School and Mel – Baradene College

Why is there a higher risk if you’re born lighter? Wouldn’t it make sense if it was due to a heavier weight?

Do we know how birth weight affects puberty age yet or do we just know that it does?

Dr Deb Sloboda - 1 April 2010

Remember that being born lighter (or small) is only a MARKER used by scientists and doctors to “guess” about what sort of conditions the baby would have developed in. Babies born light or small may have had been exposed to a decrease in oxygen, nutrients, or exposed to stress or drugs during pregnancy. We know that all of these things change a way a baby grows so we assume that a light baby would have encountered some of these conditions. The link between being born light and disease later in life is because if a baby is exposed to these “bad” conditions it will change the way it develops to suits these conditions. It will change the gene expression, protein expression of enzymes and receptors and it might be that these changes will result in higher risk of disease later in life. 

Student from Green Bay High School and Kitty – Rangitoto College

Why does birth weight affects diabetes? Wouldn’t your diet exercise lifestyle etc influence it more???

So does the mother's diet for the offspring (when it's in the womb) affect the later life conditions (i.e. diabetes and heart disease) more than the offspring's actual diet or is it vice versa? Or even equal influence?

Dr Deb Sloboda - 1 April 2010

See the previous answer and extending this – we used to think that it was really your lifestyle that predicted your disease risk but we now know that it is the INTERACTION between the two (lifestyle and earl fetal environment) that is important. Remember the girls that we investigated and we found that smaller birth weight girls went into puberty early but they also had to be fatter at age 8. This is the same data as we showed in the rats.

Student from Rangitoto College 

If you were born with a low birth weight you have an increased chance of high blood pressure and type 2 diabetes... But what if you were born with an unusually high birth weight? Like that baby in America that was about 10kg at birth.

Dr D Sloboda - 1 April 2010

The same risks are present in high birth weight babies. 

Sharon Watson – Pukekohe High School 

Have they considered if there is any significance in the way the babies are fed... if they are bottle fed earlier is there something in the formula affecting their data. Would breastfeeding reduce the risk of diabetes etc ?

Dr Deb Sloboda - 1 April 2010

Great question-again highlighting the importance of an INTERACTION between the early fetal environment and the postnatal one. Breastfeeding in general has been shown to prevent childhood obesity but how this actually happens is still unclear. Some scientists think that formula feeding interferes with the baby’s natural capability of regulating food intake.

Leon – Tamaki College 

How do the genes know what the environment is going to be like when the baby is born??

Dr D Sloboda - 1 April 2010

This is the million dollar question! We know that in animals, genes appear to be regulated by nutrients, hormones, oxygen levels so the fetus reacts to the levels of these things while it is developing and therefore the baby’s genes could potentially change. Scientists are now trying to figure out if the same thing happens in humans.

Helena – Tamaki College

Do hormonal maternal signals occur in humans? What kinds of effects does a human woman’s maternal hormonal signals have on her baby?

Dr Deb Sloboda - 1 April 2010

Yes. One important way that the mother communicates to the baby is using hormones. One really good example is stress. Really high levels of stress produce stress hormones in everyone and this also happens in pregnancy. Luckily, the placenta has a system to keep most stress hormones that the mother produces away from the baby. But under extreme circumstances the mother might produce so much stress hormone that the baby does eventually see the hormone and this hormone reacts with cells in the baby, usually making the baby grow slower or smaller.

Student from Rangitoto College

Does this mean that our metabolism is dependent on the kind of nutrition our mothers had when they were pregnant with us?

Dr Deb Sloboda - 1 April 2010

Well, yes it does. But it’s not that simple. It also means that the environment that you LIVE IN NOW will interact with the environment that you grew in IN YOUR MOTHER

Student from Rangitoto College 

Why do we have a higher risk of type 2 diabetes, obesity and high blood pressure if we have puberty early?

Dr Deb Sloboda - 1 April 2010

I think we got things a little mixed up here - increased risk of type 2 diabetes obesity and high blood pressure and early puberty are things that might happen if babies grow up in environments that aren’t great. Whether these things are all linked in biology is still unclear. There are lots of hormones that regulate puberty that also regulated fat and also regulate whether your pancreas is able to make insulin but the exact mechanisms of how they all relate to each other is still unclear.

Leroy – Tamaki College 

If you’re programmed to start early puberty is there anything you can do to delay it to "normal" timing? What about obesity and Type 2 Diabetes? 

Dr Deb Sloboda - 1 April 2010

Well it depends on what you call normal. We know now that normal is now 12 ½ years so it’s important that we don’t start going around telling everyone that if they have puberty at age 12 that they are abnormal because they are not. Therefore we are not going to go and start preventing kids from going into puberty. Scientists are trying to work out what are the things that we need to think about if in fact we go into puberty early - LIKE exercise and diet. You all have friends that eat like crazy and don’t exercise but don’t get fat and other friends that are really healthy eaters and exercise but maybe are a little tubby - why is that?? That is what we are talking about: RISK FACTORS. Also we are talking about associations not causal factors. Early puberty doesn’t make you have obesity and type 2 diabetes, the unknown thing that caused you to have early puberty probably also has caused obesity and type 2 diabetes.

Nathan – Horowhenua College 

From the observed graph Sweden shows a steep decrease in the age that puberty begins. But if the data is extrapolated further would it be possible for puberty to start at a very early age? i.e. 5 years old?

Dr Deb Sloboda - 1 April 2010

No and we would not extrapolate this graph; in fact in most populations we think that this change in age has actually plateaued-meaning that it is not decreasing further

StephP Baradene 

Anyone know if the reason why women menstruated later in historical records could be linked to a lack of sufficient nutrition that caused them to develop slower?

Dr Deb Sloboda - 1 April 2010

Reproduction and metabolism is intimately linked. The reason for this is that really the only reason organisms go into puberty is to reproduce! We are unique as a species-most species will start to reproduce and have babies immediately after entering puberty because the important thing in life to is to make sure that your genes are passed on in subsequent generations. So if nutrition is bad and infection is high and the female doesn’t have the reserve (fat, nutrition) then she won’t go into puberty-why? Because if she did then she probably wouldn’t be able to successfully carry a baby and have a good pregnancy!

Heather – Pukekohe High School

Does folic acid reduce DNA methylation?

Professor Lynn Ferguson and Michal Denny - 3 April 2010

No, the opposite is true.

Folate (the natural form of folic acid) plays an essential role in one-carbon transfer involving remethylation of homocysteine to methionine which is a precursor of S-adenosylmethionine, the primary methyl group donor for most biological methylations. The degree of methylation controls gene expression. So, when there is a state of folate deprivation, genes are undermethylated, and may become expressed inappropriately.

DNA methylation is one of the key processes in epigenetics. For more information on what epigenetics is see:

If you’re interested in the role of folate in the diet see our Teacher Professional Development Seminar on Nutrigenomics: