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"It may seem strange that we inherited disease-causing genes at all. After all, only beneficial genes should survive, so surely over hundreds of generations we

by lholden 11y ago

"It may seem strange that we inherited disease-causing genes at all. After all, only beneficial genes should survive, so surely over hundreds of generations we should have shaken off these unwanted contributions?" Certainly not my field, but my understanding is that unless a mutation has a direct impact on survival and fertility... then there is no evolutionary drive for it to go away. All animals have negative genes that just stick around as random "junk" which has accumulated over the years. It's not surprising that we have picked them up too.

beloch 11y ago
Some genes exhibit pretty complex behaviour. For example, the gene for sickle cell anemia manifests as sickle cell disease only when an individual is homozygous in that gene (i.e. They have inherited a copy of this gene from both parents). Such individuals have a host of health problems, including being more susceptible to malaria. However, individuals who are heterozygous (i.e. they inherited just one copy from one parent) for the sickle cell gene do not typically have sickle cell disease, and being heterozygous in this gene actually confers resistance to malaria. In areas where malaria is a major cause of death, the gene for sickle cell anemia is much more common than it is elsewhere.
BurningFrog 11y ago
> Certainly not my field, but my understanding is that unless a mutation has a direct impact on survival and fertility... then there is no evolutionary drive for it to go away. Well, genes get corrupted by random mutations, and if they have no survival value, there is no correcting force. So they drift out of the genome.
- rtl49 11y ago
  Are you referring to genetic drift? This is a statistical phenomenon by which alleles that are near neutral for viability change in frequency until one becomes fixed. This doesn't mean that neutral mutations will invariably push the wild type out of the genome. Actually, that would be improbable in the absence of a selective pressure or an accident of history.
  - BurningFrog 11y ago
    I'm saying genes that have no survival-value will fade away due to accumulating random mutations. That's probably different from whatever you're describing.
rtl49 11y ago
'Junk' DNA doesn't actually contain genes. By definition, a gene encodes a functional polypeptide or RNA. This is different from alleles that are neutral for viability. An example of such an allele might be connected earlobes -- this phenotype is genetically determined, but unless there's sexual selection I'm not aware of, you are correct that we wouldn't necessarily expect the alleles involved in this phenomenon to go away. However, they might as a result of an accident of history or genetic drift.

by lholden 11y ago

beloch 11y ago

Some genes exhibit pretty complex behaviour. For example, the gene for sickle cell anemia manifests as sickle cell disease only when an individual is homozygous in that gene (i.e. They have inherited a copy of this gene from both parents). Such individuals have a host of health problems, including being more susceptible to malaria. However, individuals who are heterozygous (i.e. they inherited just one copy from one parent) for the sickle cell gene do not typically have sickle cell disease, and being heterozygous in this gene actually confers resistance to malaria. In areas where malaria is a major cause of death, the gene for sickle cell anemia is much more common than it is elsewhere.

BurningFrog 11y ago

> Certainly not my field, but my understanding is that unless a mutation has a direct impact on survival and fertility... then there is no evolutionary drive for it to go away. Well, genes get corrupted by random mutations, and if they have no survival value, there is no correcting force. So they drift out of the genome.

rtl49 11y ago
Are you referring to genetic drift? This is a statistical phenomenon by which alleles that are near neutral for viability change in frequency until one becomes fixed. This doesn't mean that neutral mutations will invariably push the wild type out of the genome. Actually, that would be improbable in the absence of a selective pressure or an accident of history.
- BurningFrog 11y ago
  I'm saying genes that have no survival-value will fade away due to accumulating random mutations. That's probably different from whatever you're describing.

rtl49 11y ago

'Junk' DNA doesn't actually contain genes. By definition, a gene encodes a functional polypeptide or RNA. This is different from alleles that are neutral for viability. An example of such an allele might be connected earlobes -- this phenotype is genetically determined, but unless there's sexual selection I'm not aware of, you are correct that we wouldn't necessarily expect the alleles involved in this phenomenon to go away. However, they might as a result of an accident of history or genetic drift.