This is kind of an offshoot of the black skin thread. Are all recessive genes doomed to extinction? I don’t mean in the next 20 years, but 1000 years from now will anyone have blue eyes?
Good question—but were there blue eyes a thousand years ago?Two thousand? Three thousand?
If there were they’ll probably be around for a heck of a long time to come----northern Italy is full of blue-eyed people,and not all of them blonde!
And as for scandinavia—Well!
roksez sed: Are all recessive genes doomed to extinction? I don’t mean in the next 20 years, but 1000 years from now will anyone have blue eyes?
But of course they will! Recessive traits may go into hiding (i.e., be dominated by “stronger” genes), but as soon as two carriers of the recessive gene mate: boom, it’s back!
Only if there were a complete consensus that only brown-eyed people could reproduce would blue eyes be reduced. Even then, the blue gene would still be carried by hybrids and recurr as above.
This might be an urban legend, but it illustrates the point: a white couple produced a black baby (forgive the un-PC adjectives) because both parents were fractionally black. Their blackness was so diluted and thier family tree unknown that they honestly didn’t know their heritage. The egg & sperm that became the baby happened to get higher-than-expected blackness genes so as to make the traits more obvious.
They won’t disappear. Remember, you can have a dominant trait but still carry a recessive gene. For that reason, recessive genes won’t disappear. At least not as a result of normal sexual reproduction. An increase in dominant trait in a population doesn’t mean the recessive gene disappeared, it’s just that most of the individuals with dominant traits are carriers for the recessive ones.
The Hardy-Weinberg equilibrium deals with this idea.
Remember: A five-fingered hand is a recessive trait. Six is dominant.
Not only will recessive genes not ever get wiped out. Dominant genes that cause sterile or nonviable children dont go away either. Androplastic Dwarfism is one of these traits, its dominant, but it causes sterility, so there is no possible way to inhereit it. When reproductive cells split to reproduce, the DNA sequences can be corrupted completle naturally. Just God helping Darwin out by throwing the dice.
I breed pedigreed cats, and in the ‘cat fancy’ we have a saying: Recessives are forever.
Unless a concerted, deliberate attempt is made to eliminate a recessive gene, it will pop up frequently. Even with deliberate test breeding to try to eliminate a gene, some will still slip through because of the unpredictability of inheritance. You can predict the ‘odds’ of something being inherited, but not the actual occurence.
Dominants are much easier to eliminate, but a dominant with variable expression can go undetected in its most minimal form, and also be passed on.
Alphagene mentioned the Hardy-Weinberg equilibrium. Ths generally states that in the absence of a inherent disadvantage or advantage of a particular trait, the ratio of dominant to recessive traits in a population remains the same form generation to generation. So the answer is that they will not die out. However, it can be proven that if either trait (either dominant or recessive) is an evolutionary disadvantage, it will eventually die out unless specific steps are taken to preserve it. Of course, this could take a while considering we are dealing with largely random processes.
In response to falcon, the above is only a theoretical arguement. It is also possible for a relatively common corruption of the DNA to occur spontaneously without being passed on from the parents (I believe sickle-cell anemia is one example), thereby recreating a harmful gene. In this case, the harmful gene may not die out.
I’ve never heard of sickle cell appearing spontaneously, but it sure can be inherited! The gene is an incomplete dominant. The ‘sickling’ is caused by the production of modified hemoglobin that causes the red blood cells to be change shape when oxygen levels in the blood drop below a certain level. Heterozygous individuals (only one copy of the gene) produce both normal and abnormal hemoglobin, so only part of their red blood cells ‘sickle’ when oxygen-deprived. Homozygous individuals (two copies of the gene) have sickle-cell anemia - all of their red blood cells ‘sickle’ when oxygen deprived, which can cause a ‘sickle-cell crisis’.
High risk parents (usually blacks in the US) are encouraged to test for this before having children. It is most predominant in blacks because of the evolutionary advantage that it provides - resistance to malaria, an important advantage in some parts of Africa.
Cystic Fibrosis is seen mostly in whites and is caused by a recessive gene that is homozygous lethal - but it is theorized that heterozygous individuals are resistant to cholera.