By chance, I saw a lot of people on the Internet discussing how they could avoid inbreeding if there were only one man and one woman left on the planet. This topic is still quite interesting, after all, inbreeding is unreasonable in the eyes of our ordinary people, whether it is ethical or legal, even the marriage law has clear provisions. So today, let's talk to you about inbreeding from a biological point of view.
01, congenital problems basically do not need to worry
Why is there basically no need to worry about congenital problems? This is because in the past, the cognition of the problem of inbreeding was mainly a kind of naïve genetics, at that time people did not know more about genetic variations, but simply thought that inbreeding would exacerbate the number of homozygous fragments, but with modern genetics, especially a lot of mathematics into biology, only to find that these problems, some of the worries.
First of all, the nature of the problem of inbreeding is a genetic problem; secondly, the essence of the genetic problem is a problem of variation
Neither of these problems is a problem at this time. In fact, the problem of inbreeding, in the [group], has always been a concept dominated by human "imagination".
You can understand the folk livestock breeding and domestication, and you will find that this is simply a nest of close relatives. I recently ventured into this field and learned that close relatives are in the domestication and breeding of animals, and the frequency is simply high. Many enclosed areas, such as those mountain villages, are often responsible for population breeding for decades or even hundreds of years, and the diversity of offspring is very rich.
On the other hand, human beings, groups of pure close relatives who marry, do not seem to be effectively observed at present, so human beings are more of a theoretical speculation. If you really want to worry, it is better to consider the problem of infertility and the smooth growth of offspring, because the proportion of these two problems is much higher than the proportion of genetic diseases.
Let's talk about this problem.
02, inbreeding
I recently started dabbling in an interesting area: inbreeding.
As the name suggests, inbreeding refers to mating and reproduction between individuals with very similar blood relations or between individuals with very similar genetic composition.
This common problem on the plant (self-inbred and backcrossed in high school) is estimated to be much less on animals, and it is very difficult.
Why? Because experience tells us that animal inbreeding will encounter a serious problem of inbreeding decline, it is estimated that some people will immediately say, is this not exactly the problem of close relatives marriage that we humans are worried about?
However, the answer is just the opposite, because the animal's severe inbreeding is the result of each generation having to force inbreeding, and in order to force them to increase the inbreeding coefficient, it is basically mother/child/father-daughter (brothers and sisters are actually very different genetically), and even so, inbreeding decline is predominantly after five or six generations.
Because of this, there are actually very few inbred lines of animals, mainly mice, which have been around for a hundred years, and there are currently pigs and other inbred lines.
So, here are two basic questions:
1, must be strict mother/child/father-daughter inbred
2, probably around the 5-6 generations of inbreeding recession
This is the conclusion reached by many animal experiments.
03, why are close relatives banned within three generations?
So, the question is, a couple, how neurotic are they, do they have to engage in mother-son/father-daughter on behalf of each other? In fact, as long as it is not deliberately done, after three generations, there is basically no need to worry about inbreeding.
Speaking of which, I am reminded of another very interesting question, that is, the question of why close relatives are forbidden within three generations.
In fact, a big premise of this problem is that couples have recessive genetic diseases, otherwise, you are free, there is no genetic disease, unless it is born to mutate, otherwise how can you have a genetic disease?
And why three generations? Because in the fourth generation, the probability of genetic diseases is lower than the probability of population sporadicity.
Therefore, there is basically no need to worry about inbreeding.
04, how did the inbreeding problem be overcome at the beginning of the birth of the species?
A distant question comes: how did species survive in the first place?
Of course, you will definitely think of a basic high school knowledge, the law of gene separation, for 3 billion base pairs of humans, the diversity of separation is very large, so even if it is brother and sister, there will be a big difference.
One of the more interesting problems is that organisms seem to have an ability to avoid homozygous problems, which is an interesting problem in genetics at present, and it is also a problem we encounter when studying inbreeding and parthenogenesis:
That is, when we tried to produce animal offspring using the strategies of parthenogenesis and inbreeding, we found that some fragments would certainly not be homozygous. Because homosexuals cause death. You may think that this is a purely evolutionary problem, but in practice, we find that this proportion is actually higher than normal evolution allows, so there must be some biological factors that we have not yet discovered that play a role in fertilization or embryonic development.
For example, a current theory is the role of the placenta in embryonic development.
In the recently published nature article "Inherent mosaicism and extensive mutation of human placentas", a very interesting problem is mentioned, that is, in fact, during human development, there will be many genetic abnormalities, even chromosomal abnormalities, however, these abnormalities will be absorbed by the placenta, leaving those normal to continue to move forward.
It can be said that the placenta is a fault correction mechanism.
I think there must be more than one error correction mechanism in biology to maintain normal development.
Just like many people think that cell development is 1-2-4-8-16-32, but the real situation, rarely this kind, this is also what we find when we look at the embryo, often a range, that means that some cells develop and develop, they are eliminated, even in the early embryonic stage (this time is all-powerful, each can develop into an individual).
Of course, if you have to say, is to find a bunch of genetic disease couples, they can really guarantee that the child through childhood to grow to sexual maturity, then, with this technology, it is not too easy to produce mutations?
There are simply not too many ways to make mutations in biology, and aren't we mainly studying genetic variations as molecules?
Physical, various rays
Chemical, various mutagens
Biological, some viruses.
And even we have a lot of gene editing methods.
In fact, the longer I do genetics, the deeper my understanding of genetics, but there is a deeper understanding of the knowledge that genes determine everything, that is, genes do not seem to be so, especially I myself am in the field of evolution, and I do not think that it will be so subtle in the beginning. And now I have a more and more bio-chemical-physical way of thinking. Behind the biological is chemical, behind the chemistry is physical.
Many of our biological phenomena, early on, must not be very delicately mixed, but there are some other factors at play, such as why do fertilized eggs start to divide? Why does the division go on to the polyderma? Could a fertilized egg record that much information? I don't approve. I think behind it is more driven by the influence of chemical factor stimuli, concentration gradients, gravity, position (left and right inside and outside) and so on.
pss: Inbred lines are very valuable in biomedicine, because of high genetic similarity, stable traits, so in order to avoid problems due to individual differences, in fact, everyone often says that mice, often inbred lines.