Index
They refer to the group of conditions where there is an abnormality, either in the number or structure of chromosomes in a cell.
This could be seen as a large-scale mutation , occurring above the level of change in nucleotide sequences.
Several genetic diseases are related to chromosomal aberrations.
Types of chromosomal aberrations
Numerical
Nondisjunction of chromosomes in meiosis, in the production of parental gametes , is the mechanism for the production of chromosomal aberrations.
It results in the production of parental gametes, with more or less than the normal haploid number of chromosomes.
Fertilization involving one gamete of this type and another normal can result in a zygote that is trisomic for the involved chromosome or is chromosome deficient.
Numerical abnormalities are typically referred to with the suffix: somy. The usual situation in a diploid cell is disomy, having two copies of each chromosome.
When a homologous pair of chromosomes loses or gains a chromosome, this disrupts the total complement of chromosomes in that cell so that it is no longer a multiple of the monoploid number (X). This phenomenon is called aneuploidy.
A monosomy is the loss of a chromosome, while trisomy, tetrasomy, etc. they involve the gain of chromosomes.
Examples of genetic diseases in which a numerical abnormality has occurred:
Turner syndrome
It occurs only in women. It occurs due to alterations in the number of X heterochromosomes, generated by the association of a gamete carrying an X chromosome and another lacking the chromosome.
It is a monosomy that causes certain cardiovascular disorders, infantile features, moderate mental retardation, absence or atrophy of the uterus, fallopian tubes and ovaries, without reaching sterility.
Síndrome de Klinefelter
It only occurs in men. This variation in the number of heterochromosomes occurs when the gametes have an additional X chromosome (karyotypes 47, XXY and 49 XXXXY).
These chromosomal aberrations present generally tall, sterile individuals with underdeveloped gonads, large pectorals, and small testes.
Patau Syndrome
It is a trisisonomy of chromosome 13, somatic cells have 44 autosomes, two heterochromosomes and an additional chromosome 13.
The characteristics of babies with this syndrome have mental deficiency, deafness, polydiactyly or the presence of more than 5 fingers on one of the hands or feet, the presence of a cleft lip and some heart abnormalities.
Down syndrome
Chromosome 21 trisomy is a condition that occurs when somatic cells have three chromosomes 21.
The phenotypic characteristics are mental retardation, short stature, slanted eyes, very rounded face, flat nose, small ears, short neck, affections of the cardiovascular system, sterility and wide and short hands, among others.
Triple X syndrome
This abnormality occurs only in women who have an extra X chromosome.
This abnormality causes some learning disorders, almost no complications in newborns, women are generally tall, with normal intelligence and are fertile.
Structural
These are consequences of the breakdown of the chromosome, followed by a reconstitution of an abnormal combination.
These alterations in the chromosomal structure caused by breakdown may be able to leave unchanged after cell division, or unstable.
Cree-du-chat syndrome
Individuals with this syndrome have a deletion in part or all of the short arm of one of the two chromosomes 5.
It causes premature death and presents characteristics such as severe mental and growth retardation, microcephaly, hypertelorism, antimongoloid and epicantus eyelid folds, small ears and jaw, difficulty eating, swallowing and sucking, teeth projecting forward.
At birth there is a lack of development of the larynx which causes the characteristic cry like a cat.
Prader-Willi syndrome
It is a genetic alteration generally caused by genetic changes in the “unstable” area of chromosome 15, it is a very rare syndrome that presents a clinical picture of obesity, short stature, cryptorchidism and learning disorders.
Angelman syndrome
It is caused by the loss of a part of chromosome 15, which is contributed by the mother.
It causes neurological disorders with severe learning difficulties, associated with facial appearance characteristics of happiness.
X fragile syndrome
This disorder is a consequence of a change or permutation in gene 1.
It causes mental retardation, poor eye contact, reluctance to touch, flapping, hand chewing, and shyness or social anxiety and attention problems .
Inheritance of chromosomal aberrations
- The child can inherit a completely normal chromosome arrangement.
- The child can inherit the same chromosome rearrangement as the father.
- The child may be born with a learning disability, developmental delay, and / or health problems.
- The pregnancy can end in miscarriage.
Therefore, it is generally possible for a person who carries a chromosome rearrangement to have healthy children.
A child can be born with a genetic aberration even though the chromosomes of both parents are normal. In this case, the probability that the parents will have another child with the same rearrangement is usually very low.
