This article is from WeChat public account:< span class = "text-remarks"> Global Science (ID: huanqiukexue) , author: Sarah Zhang, translation: to Yingzhuo, original title: < /span> “Breaking textbook theory: the number of chromosomes your parents give you may not be the same”, title map from: Visual China
According to meiosis and fertilization, the newborn’s chromosome should be half from the father and the other half from the mother. If this rule is wrong, it may lead to certain genetic diseases. However, the recent study published in the American Journal of Human Genetics unexpectedly found out from the analysis of gene big data that the composition of the parental source of chromosomes in many healthy people is not 1:1.
Image Source: Cold Spring Harbor Laboratory
Unexpected chromosome composition
After Natalie Nakles was born, even before the maturity of her mother’s eggs, strange things happened. The egg should have only one chromosome 16, and the result is one more. Subsequent a series of cellular processes removed the chromosome 16 from the sperm when the fertilized egg of Nakles developed. Therefore, the 24-year-old Nakles does not inherit a set of chromosomes from their parents like most people. Her two chromosomes 16 are all from her mother.
This phenomenon is called “single parental dimorphism” (uniparental disomy), which is two of a pair of 23 pairs of chromosomes The chromosomes are all from the father or mother. In the literature, single parent dimorphism is closely related to spontaneous abortion. Even if the fetus survives, it may have diseases such as skeletal abnormalities, epilepsy, mental retardation, and childhood cancer. Nakles suffers from Asperger’s syndrome, an autism spectrum disorder that does not have language and intellectual disabilities in people with autism. In addition, she is very healthy and has no serious health problems. She sent the saliva sample to 23andMe for DNA testing before she found that she had a single parent.
Today, a study tested about 4.83 million people, of which 4.4 million came from 23andMe genetic testing companies and 430,000 from British biological samples. The results show that many healthy people like Nakles have single-parentality. A total of 675 samples of single parent dimers were found in the study and were not found to be significantly associated with any harmful features. This suggests that the single parent dimorphism is more common and less harmful than the results in the past literature.
Weny Robinson, a geneticist at the University of British Columbia, did not participate in the study, but she was very excited about the results. She previously suspected that the incidence of single-parent dimorphism in healthy people was higher than reported in the literature, but there was no DNA sample data support. Because until recently, more healthy people who volunteered for DNA testing have grown up. In general, doctors may find that some patients have a rare disease before they are allowed to carry out DNA testing. As a result, they found a single parent, and then published a related article. It’s like looking for flower pots just under the streetlights and you can conclude that all the pots are under the streetlights.
Image Source: pixabay
However, the 23andMe and British biobanks are more healthy people, and the results suggest that even healthy people may have seemingly serious genetic abnormalities. Robinson believes that this anomaly is actually a normal phenomenon. The existing scientific research essentially enumerates all the factors that may lead to harmful results, so people mistakenly believe that genetic abnormalities only occur in people with serious diseases. Prenatal examinations sometimes find and list single-parent dimers, which can make prospective parents feel very anxious. However, this new study can dispel their anxiety to some extent. “If you have a single parent, it does not mean that your child will have problems.”
wrong start
Ameiosis is the process of forming eggs and sperm, while single-parent dimorphism is the result of an error in this process. Scientists have also proposed various mechanism hypotheses, but the most common situation may be this: meiosis errors lead to two identical numbers of chromosomes in the egg or sperm, so the embryo finally gets three Homologous chromosomes. These embryos sometimes spontaneously abort, but sometimes they can do “three-chromosome self-rescue”, that is, some cells will lose an extra third chromosome and eventually defeat abnormal cells. As a result, the fetus will eventually get the correct number of chromosomes, but since the chromosome that was lost is random, the fetus’s genome is not necessarily exactly half from the father and half from the mother.
Although this is not sperm