Difference Between Autosomes and Sex Chromosomes

The human body is composed of 46 chromosomes, which is often said to be formed by 23 pairs of chromosomes. The 23 pairs of chromosomes include 22 pairs of autosomes and 1 pair of sex chromosomes. Most people do not have a special understanding of autosomes and sex chromosomes, and it is easy to confuse the two. In fact, a pair of sex chromosomes is used to determine gender. If the chromosomes are abnormal, it means that the fetus may suffer from disease. Therefore, it is necessary for both men and women to do a check-up before pregnancy.

Autosomal recessive inheritance refers to the inheritance of traits controlled by recessive genes on autosomes. If the disease-causing gene is recessive and located on an autosome, the disease will not occur in the heterozygous state because the action of the normal dominant gene can mask the action of the disease-causing gene. The disease will only occur in the homozygous state. This disease is called an autosomal recessive genetic disease. The traits expressed in its offspring may not be expressed in its parents. A heterozygote who does not show clinical symptoms but carries the disease-causing gene is called a carrier, and his disease-causing gene can be passed on to his offspring.

Autosomal recessive trait

1. Since the disease-causing gene is located on the autosome, the transmission of the disease-causing gene has nothing to do with gender, so men and women have an equal chance of getting the disease. 2. The patient's parents are often healthy, but both are carriers of recessive disease genes; 1/4 of the patient's siblings will become ill, and 2/3 of normal siblings have a 2/3 chance of being carriers of recessive disease genes. 3. The patient's children generally do not develop the disease, and there is no phenomenon of continuous transmission in the pedigree, and cases are often sporadic. 4. When close relatives marry, the risk of recessive genetic diseases in offspring is significantly higher than that of random marriages.

Common autosomal recessive inheritance includes sickle cell anemia, phenylketonuria, albinism, etc. 1. Sickle cell anemia Sickle cell anemia is a disease caused by a defect in the β-globin gene and is inherited in an autosomal recessive manner. Because the 6th amino acid glutamic acid in the β-peptide chain is replaced by valine, sickle hemoglobin (HbS) is formed, replacing normal Hb (HbA). Sickle cells cause increased blood viscosity, which can easily lead to embolism of small blood vessels, causing sporadic local tissue hypoxia and even necrosis, resulting in painful crises such as musculoskeletal pain and abdominal pain. At the same time, the deformation ability of sickle cells is reduced. It is difficult for them to deform and pass through narrow capillaries. They are prone to rupture when squeezed, leading to hemolytic anemia. 2. Albinism Albinism is a group of single-gene autosomal recessive genetic diseases caused by abnormalities in the tyrosinase gene on the long arm of chromosome 11, which leads to reduced or complete lack of melanin biosynthesis. The patient's skin appears white or pink, and his hair is white or light yellow, accompanied by amblyopia, photophobia, nystagmus, etc. 3. Phenylketonuria Phenylketonuria (PKu) is a common amino acid metabolic disease caused by enzyme defects in the phenylalanine metabolic pathway, which prevents phenylalanine from being converted into tyrosine, resulting in accumulation of phenylalanine and its ketoacids and their massive excretion in the urine. It is an autosomal recessive inheritance. Affected children are born normal, and symptoms usually begin to appear at 3 to 6 months of age. In the early stages, there may be neurobehavioral abnormalities such as excitement, hyperactivity or drowsiness, which may be followed by obvious intellectual development lag. In severe cases, hypotonia and convulsions may occur. In addition, there may be a decrease in pigmentation, dry skin, and urine may have a special rat-like odor.

Sex chromosome abnormality is a type of human chromosome aberration. Sex chromosome deletion, duplication, inversion, and translocation can all lead to sex chromosome abnormalities. Those with mild symptoms can lead a normal life, while those with severe symptoms can undergo sex reassignment surgery. Congenital hereditary hermaphroditism is accompanied by developmental abnormalities, such as the onset of developmental disorders or abnormalities of secondary sexual characteristics during adolescence, and some sex chromosome abnormalities are accompanied by mental disorders. In addition to congenital factors, single gene defects and environmental factors can also cause sex chromosome abnormalities. The diagnostic method uses peripheral blood chromosome G-banding karyotype analysis and fluorescence in situ hybridization (FISH) technology to analyze sex chromosomes. Spontaneous abortion, stillbirth, premature death, and congenital diseases are important causes of sex chromosome abnormalities and male and female infertility.

Diseases caused by sex chromosome abnormalities 1. Congenital ovarian hypoplasia: The incidence is 10.7/100,000 newborns or 22.2/100,000 female babies. It accounts for 6.5% of embryonic deaths. It is the most common abnormality of sexual development. The single X chromosome is mostly from the mother, so the lost X chromosome may be caused by nondisjunction of sex chromosomes in the father's spermatocytes. Only 0.2% of 45,X fetuses reach full term, and the rest die between 10 and 15 weeks of gestation.

2. Seminiferous tubule dysplasia: also known as Klinefelter syndrome, is a sexual development abnormality with an abnormal number of chromosomes. The typical karyotype is 47,XXY, and mosaicism may also occur. The gonads are dysplastic testicles. The incidence rate is 1:600 ​​to 1:1000 male infants.

3. Super-female: The risk is greater when the mother is older. The characteristic of multiple Xs is mental retardation. There are also reports of 5 Xs. The more Xs, the more severe the mental retardation. It is often misdiagnosed as congenital idiocy in clinical practice.

4. XO/XY gonadal dysgenesis: The chromosomes of this type of patient are 45,X/46,XY. It was initially discovered that the gonads of this type of patients were underdeveloped testicles on one side and cord-like gonads on the other side, so it is also called mixed gonadal dysgenesis. The clinical features include Turner syndrome, and some patients may have clitoromegaly.

5. True hermaphroditism: True hermaphroditism may have various mosaic sex chromosomes, or normal 46,XX or 46,XY sex chromosomes.