The "curse" of inbreeding
Inbreeding , a problem that has been talked about since ancient times. Why do you say this?
Whether it is the kings of the past dynasties at home and abroad, or the modern biomedicine , it has been shown through various aspects of research and emerging phenomena.
Inbreeding is harmful almost at any time, and the harm is huge, and it can completely cause a devastating blow to a race.
If reproductive isolation is a protective lock added by nature to biodiversity , then inbreeding is the destruction program left by natural selection to living things.
A "curse" from genes, Any species that wants to try to inbreed will eventually be backlashed, and cannot be cracked .
The so-called inbreeding is easy to understand in a literal sense.
But from a biological perspective, it is through the mating or reproduction of offspring. Due to incorrect gene expression , genetic diseases that endanger life will eventually occur.
For animals , inbreeding is only biological chaos.
and In terms of for human society, inbreeding has a devastating blow from both a moral perspective and the continuation of the human race.
Inbreeding caused by political marriages in European dynasties
Generally speaking, the most common form of inbreeding is congenital birth defects, also known as congenital diseases.
It is an abnormal condition that exists at birth. The most obvious characteristic is that there will be physical and intellectual disabilities, or there will be developmental disabilities .
This type of disease occurs because the pairing of the parent gene has a 25% probability of producing the binding factor . The two copies of the chromosome or gene in the binding factor have the binding of the same gene sequence as . .
In other words, it is the degree of similarity of the allele in an organism to .
binding factors will affect DNA transcription
Due to the high homozygosity rate of this binding factor , malformations or harmful characteristics may remain in the population, which will cause the population to become fixed in some characteristics.
For example, there are too many bones in a certain area, abnormal growth in some joints, etc.
From the perspective of genetic diseases , the recessive genetic disease in the normal dominant gene is the main source of problems. It occurs when there are alleles two copies of specific The silent gene mutation .
in some special cases, such as new mutations or uniparental disomy. For individuals with the disease
, usually both parents may be carriers of the gene, but as carriers they do not show any signs of mutation, and the reason for carrying the mutated gene is not known.
The combination of recessive gene inheritance may
But because relatives share a higher proportion of genes than between non-relatives, it is more likely that parents who are related by blood are both recessive, etc. carrier of the gene.
Therefore, the offspring born from such a relationship will have a higher risk of suffering from autosomal recessive genetic diseases.
And the degree of increased risk depends on the genetic relationship between the parents . For example, if both parents are close relatives, this risk is greatest.
Relationships between distant relatives are at moderate risk, although the proportionality factor is still higher than in the general population.
The mystery of genetic inheritance
In summary, the specific expression of dominant genes and recessive genes determines the diversity of human gene segments .
Everyone inherits a set of genes from their parents, so everyone has 2 genes for each specific trait.
The most classic cases are earlobes, hairline shape, hair color, etc.
A person may have two of the same dominant genes at the same time, or one of each.
In this case, the expression of one gene usually masks another gene . The masked gene is dominant , and the masked gene is recessive.
Dominant genes and recessive genes
Therefore, From the perspective of gene expression, , if there are dominant and recessive genes in an individual, only the dominant effect is visible.
So for the effect of a recessive gene to be visible, both genes must be recessive.
So, how does inbreeding gradually deplete this gene expression , eventually leading to the destruction of the population?
As mentioned above, inbreeding is basically breeding between genetically closely related individuals. .
There are two copies of each gene
Looking at with a simple analogy, consider 2 unrelated people , such as A and B.
Everyone has 2 genes, let's call them 1, 2 and 3, 4 for now. Then the combination of the descendants of A and B can be any combination among these 4 numbers.
However, if there is a genetic correlation between AB , then they will have at least 1 similar gene, that is, 1, 2, or 2, 3.
Just from the mathematical perspective of permutations and combinations , and their descendant combinations will become less .
This causes the same genes to be shuffled between generations, and the pairing between recessive genes will be more obvious.
heterozygote combined with
. If any of these 4 numbers, , represents the defective disease in the gene.
Since A and B have the genetic gene and related , then their offspring will inevitably become carriers of .
For humans, , everyone has more or less harmful recessive genes, and once expressed, it is likely to be fatal.
Such as color blindness , sickle cell anemia and cystic fibrosis , etc. These diseases can be inherited and controlled by recessive genes.
Sickle cell anemia affects the normal function of red blood cells
Since increases the chance of expression of the deleterious recessive allele , it is possible to reduce the fitness of the offspring.
As inbreeding continues, the genetic variation will disappear and gene homozygosity will increase.
In this way, the harmful gene in the recessive gene will be further expressed in the homozygous allele.
As early as the 19th century , Darwin conducted extensive research on the adaptive consequences of inbreeding.
This reproductive model already made people aware of the impact on offspring mortality and overall health.
By in the 20th century, biological research further extended it to its debilitating effects on human organs.
Biological research will extend to the effects of human organ failure.
Unbreakable protective mechanisms
Problems caused by inbreeding include, but are not limited to, reduced fertility of offspring .
Due to the further expression of binding factors, the destruction of normal genes has made it difficult for offspring to reproduce new lives , which in turn has led to a decrease in the birth rate .
Inbreeding has a great impact on offspring.
Similarly, during the growth of offspring, the mortality rate of infants and children will be higher , and the body size will also be smaller than normal.
The expression of the recessive gene brings about the decline of immune function and the increase of cardiovascular disease risk .
even the appearance will become uglier, facial asymmetry is obvious in .
The immune system plays an important role in resisting germs
Not only that, scientists also found that inbreeding is also highly expressed in depression.
In the European Middle Ages, experienced long-term inbreeding due to changes in royal power. Perhaps the most famous one is Spain's Habsburg dynasty .
The family genealogy has become very confusing since 1661.Charles's mother was also his father's niece, and his grandmother was also his aunt.
Charles himself was also troubled by many genetic diseases. For example, he could not speak until he was 4 years old, and his jaw was severely deformed and he could hardly chew.
Eventually this dynasty ended with Charles II 's infertility, and his autopsy report more or less illustrates the role of recessive genes in these diseases.
The family tree of Charles II of Spain is very confusing
For animals, , inbreeding is also rare.
However, in comparison, animals are genetically more tolerant of inbreeding than humans, but they will also suffer from various genetic diseases, which will eventually affect the entire race.
When we move down the biological hierarchy one level further to the insect world , the dangers of inbreeding become less serious..
Insects such as bed bugs and fruit flies not only are not affected by gene expression, but inbreeding is also a way for them to continue the vitality of their race.
Inbreeding is also common in meerkats
But no matter what, the genetic diversity will become worse and worse due to the lack of in gene expression, whether it is an animal or a plant.
After the gene diversity becomes worse, , organisms' resistance to disease will further decrease .
Generally speaking, inbreeding will always destroy a race in one way.
Genetic diversity ensures the continuation of the species
Just like the fruits in the fruit plate , if one of the fruits rots and is not cleaned up, then as time goes by, the remaining fruits will also be "infected" one after another.
The final result is that the entire plate of fruit will rot. On the path of continuous biological evolution, nature has already made a choice for us.
