A question about genetics

[Mark]

Thanks everyone for the very good answers, I've a lot to read up on. On the same note, BBC2 Darwin's Dangerous Idea presented by Andrew Marr http://www.bbc.co.uk/programmes/b00j6r1b is on TV now, I saw it last week and it covers some of this.

[annaj]

Xena, it wasn't me that brought up age and fertility, but since you've addressed your post to me I thought I'd respond.

Fertility declines with age in both men and women. As you said, woman are born with all their eggs stored in immature forms in the ovaries. Until the late 90s they theory was that delcine in female fertility was due to problems with implantation in the mature uterus. However, work in the late 90s showed that egg quality starts to decline with age and chromosome degeneration can be seen in the eggs of older women. Fertility in women decreases significantly over the age of 35.

Women over 35 are also more at risk of miscarriage and certain chromosomal abnormalities, such as Down's syndrome.

More recently decline in male fertility with age has also been recognised. With increasing age sperm volume, motility and morphology all decrease. Although in men these effect seem not to be significant until later and fertility does decrease until the age of 40-50.

So, how fertile a couple are will depend on many factors. Age of both partners is important, but there are a host of other intrinsic and environmental factors that are also important.

I have to say there's an awful lot of pseudoscience on this thread. Huguenot, I would be really interested to read the reserch you mentioned about environment changing genetics, but until I've seen some evidence I'm going to remain sceptical at best about statements like financial security and lower stress leading to lower rates of genetic mutation.

[charliecharlie]

Parents A have three children, two when there were young and one (as often happens) when they were much older... does this mean that the youngest child is more evolved... no, same gene pool, differing parenting experience!

Please answer the following exam question.

A couple have a baby, the mother is 20, the father - who for the the sake of argument, is Ruben Gonzales, the Cuban pianist (who had his last child when he was 83) and is clearly a lot older...

The child is part wise and part foolish. Please explain which part is inherited from which parent and why...

http://image.maniadb.com/images/album/181/181064_1_f.jpg

and no... before we get any quips on it... the girl by the piano is not his wife!

[JimmyP]

Genes have nothing what so ever to do with ?experience?. Genes are simply messages which code for, at the basic level, production of proteins. They also code for certain phenotypes or traits such as the smooth vs wrinkled peas used in Gregor Mendel?s experiments. Therefore ?life experience? is something nurtured and would be different for generically identical organisms living in completely separate environments.

Evolutionary traits are passed onto every generation from the parents. Half of these traits come from the mother and half from the father. As a result not all of the phenotypes from the parents are passed on. In addition the recombination of genes from mother and father may interact in a different way to bring about a totally new phenotype not found in the parents. How many dark haired parents do you know with a blonde child?

Evolution does not assume reproduction is curtailed but that survival is curtailed in those that are not fit enough for the given environment. This is where Darwins? ?survival of the fittest? theory comes in.

How long the evolutionary process takes to confer a certain phenotype rendering a whole species fitter to survive is dependent on the genetic complexity of that organism. The more complex the genetic makeup the longer it takes to evolve. From current thinking part of the evolutionary process arises through DNA?s inability to replicate itself correctly 100% of the time, leading to genetic mutations. The length of ?time? it takes for a specific mutation or mutations to arise coding for a certain phenotype very much depends on how often the DNA is replicated and how ?big? that certain gene is. It would be quicker for a gene 10 bases in length to give rise to a ?fitter? phenotype that a gene that is 100 billion bases in length (bases are the constituent parts of DNA, three of which code for an amino acid when making proteins). Just think how every year, if not several times a year, a new ?flu virus infects thousands or millions of people. This is simply an evolution of the last ?flu virus. Because the genetic makeup of the virus is so simple any change caused in the reproduction of it?s genes gives rise to a new strain. As humans have such a complex genetic makeup, we cannot adapt (evolve) fast enough to predict the next strain of ?flu that is around the corner. However, this example is complicated further by the human immune system, which can evolve by itself...

My comment above assumes that only one gene codes for a certain phenotype. In fact multiple genes can code for a given trait, which explains my comment above that genes passed on from parents can give rise to completely different phenotypes to those present in the parents. If a trait is ?fitter? for the environment and coded for by multiple genes then all these gene need to be passed on in their entirety and without mutation to the next generation. The probability of this happening is small as DNA coding and replication is simple but fallible.

In fact today?s race will most likely not be any ?fitter? to survive today?s environment than humans were 2000 years ago. Yes, we might be more technologically advanced but there is a strong argument to say that this is not evolutionary. Again if you look even further back to the ancient Greeks, who?s to say that we are more evolutionarily advanced then them? The Aborigines of Australia are said to be the oldest race in the world. It?s thought that they date back millions of years. They have a very small gene pool as they were cut off from humans of the same species for such a long period of time on their native island and therefore did not share mutations from other areas of the world so readily.

Mockney?s comment of us all being ?the result of an unbroken chain of successful procreation? has some truth. In humans the DNA found in the energy producing parts of each of our cells, called mitochondria, for both males and females is inherited from the mother. Therefore we can trace the lineage of this DNA to one ?Mitchondrial Eve? the mother that started the whole process, which in turn gives rise to an ?Out of Africa? theory where the human race as we know it came from.

Charliecharlie, who?s to say whether the wise part or the foolish part of the child is deemed ?fittest? in the given environment. Also as the child has inherited half of it?s traits from it?s father and half from the mother it could very well be that both parents were part wise and part stupid. On top of this how do we know that stupidity or wisdom is coded for by a simple recombination of the genes from both sets of parents. It could be that mutations occurred or that the phenotypes are coded by multiple combinations of several genes. Most likely though wisdom and stupidity are nurtured traits, which are not governed by the child?s genotype. I won?t go near the whole argument of Asbergers Syndrome making males more genetically predisposed to various forms of ?intelligence?, which in fact is more probably an easy of performing certain tasks. Who?s to say what stupidity and wisdom are anyway?

[annaj]

Fantastic post JimmyP, thank you!

[charliecharlie]

Well Jimmy P

I am duly impressed

10/10 for the fascinating essay

(I was sort of joking and did not expect such a fine tome but, wow...)

You win the EDF Academic Award of the Year

(no, hang on, maybe that will start all sorts of in fighting, so let's say Academic Award of the Thread)

May I formally present you with this trophy

http://www.craphound.com/images/VRTABLESERAT.jpg

[JimmyP]

Thanks. It turned out to be a bit of a missive. You need a medal for wading through it...

There are so many misnomers about genetics fuelled by ill informed sources in the media. Even the BBC?s recent programmes on Darwin state some points as fact that have either not been explained properly or are completely untrue. ?Popular Science? is a bugbear of mine.

[mockney piers]

I was wondering upon a scenario where the extra time prior to copulation might be an evolutionary advantage.

How about a slightly weedy (that's his genes dictating that) mayfly who just couldn't be arsed to compete in the mayhem of the one day matefest that mayflys have to go through.

Then the following day, mere hours before his death he happens upon a mate with a similar affinity to live a bit longer (possibly due to a genetic propensity to conserve energy). They find each other easily due to lack of competition.

10 years later when their larvae emerge as mayflys a few of them end up in a similar scenario.

50 generations later you have a definite new branch of the species, the 2 day mayfly.

Am I barking up the wrong reed?

[annaj]

Genetics are really not my area, but I know what you mean about media science, JimmyP.

Are you a Ben Goldacre fan?

Edited because I dithered over "genetics are" or "genetics is" and then mockney posted between JimmyP and me so it didn't make sense anyway.

[Brendan]

Fruit flies maybe Mockney

http://news.bbc.co.uk/1/hi/sci/tech/3790531.stm

[JimmyP]

AnnaJ - Now you've introduced me to him. Maybe.

I did a Biological Sciences degree where genetics made up a significant part. Don't ask me about immunology as it's way too complicated and i didn't pay attention in those lectures... Genetics was one of the main things I 'got' and especially Developmental Biology. Another role of genes is to express themselves in different areas of an embryo to create different parts of the body or organism. It's actually very elegant. You can also see marked similarities with developmental gene expression in various different kinds of organism, say flys, frogs and mice. Almost like seeing the evolutionary process in action...

[woofmarkthedog]

Yah

[annaj]

His book is great Jimmy, and his website is worth keeping an eye on.

He sometimes borders on arrogant, but I guess that can happen when you know you're almost always right.

I tolerated genetics at medical school, but wouldn't say I "got it" and now am very rusty as it's not really anything to do with my day to day work, so I'm grateful for the refresher course your post provided and for you saying what I wanted to, but couldn't quite put together.

[Zaardvark]

Hi,

A few things

50 generations is unlikely to be enough time for there to be significant effects of selective pressure.

Experience is thought to affect the activity of genes (the amount a gene is expressed) via what are called epigenetic mechanisms. These changes may be partly heritable but the extent to which they are is unknown and it would (currently) seem unlikely that all bar a small few of these changes would persist beyond a couple of generations.

The biggest issue, as far as I can see, is that having kids at 20 is physiologically easier than at 30, and children of the 20 year olds would have a better chance of their parent looking after them until adulthood especially as 2000 years ago the average life expectancy would have been ~40.

Parents starting at 30 would also have fewer kids for obvious reasons and, combined with more complications in birth, overall it would seem to me that the group with younger parents would have some advantages as well as being considerably more numerous.

Best

Z (sometimes a geneticist)

edited (more than once) for spelling

[Huguenot]

There you go Annaj. Recent study implicating evironmental influences on genetic traits...

MIT's a pretty august body.

"In Feig's study, mice genetically engineered to have memory problems were raised in an enriched environment--given toys, exercise, and social interaction--for two weeks during adolescence. The animals' memory improved--an unsurprising finding, given that enrichment has been previously shown to boost brain function. The mice were then returned to normal conditions, where they grew up and had offspring. This next generation of mice also had better memory, despite having the genetic defect and never having been exposed to the enriched environment. "

[Huguenot]

More sepcifically...

"In a second study, researchers found that rats raised by stressed mothers that neglected and physically abused their offspring showed specific epigenetic modifications to their DNA. The abused mice grew up to be poor mothers, and appeared to pass down these changes to their offspring."

[annaj]

Thanks Huguenot, I've got the original reference from Pubmed.

I'm preparing for a critical appraisal exam at the moment, part of the monster, four-part "exit exam" that will finally mark the end of my training and qualify me for a consultant post, so I'll get a copy of the full text at work tomorrow and appraise it for my weekend homework. I'll let you know what I think.

[Huguenot]

I'm in awe.

[annaj]

No need for sarcasm.

Your admiration of robust science and belief in evidence based medicine is hardly a secret, I'm just saying I'll treat this paper objectively and see what I make of it. At first glace it looks really interesting and compelling, but the whole point of objective reading and critical appraisal is not to be swayed by the headline, or abstract, but to assess the research on its merits.

Edited for rogue apostrophe.... again.... must try harder.

[Peckhamgatecrasher]

Unworthy Anna. I rather think like the rest of use, H is in awe of your imminent status acquired after years of slog.

[Huguenot]

Oh bollards :'(

I was being genuine. I'm afraid that I was slapdash with my own education, and to my eternal shame could never be fecked to work even the bare minimum. I'm full of admiration for your work, and wish I could have done it.

I only try and make up for it by reading popular science mags now.

Hoist by my own petard I guess, but I'm sorry you thought I was being flippant.

[annaj]

Hmmm, maybe PGC and thanks, but I suspect not.

The man himself has gone uncharacteristically quiet (is it bedtime in Singapore?) so we may never know...

[Huguenot]

Cross post.

[annaj]

Spectacular cross posting.

Huguenot, I apologise. Based on our recent spats I thought you might be bearing a grudge.

PGC rightly called me on it.

Sorry :-$