Hello

i want notes on chromosomalabnormality and maladjustment.. Could not find them anywhere....
Can anybody help ?

chromosomal abnormality and maladjustment, are in Biology Book of 2nd Year published by Punjab Text Book Board

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Chromosomal abnormalities
Organized in two main groups i.e
1. Numerical
2. Structural
It has several forms i.e
2.1 Deletions
2.2 Duplications
2.3 Translocations
2.4 Inversions
2.5 Rings

Developmental abnormalities
Caused by two factors i.e Heredity and environmental factor also termed as nature and nurture respectively

Any disturbance in the chromosome can cause maladjustment....e.g monosomy, klinefelter's syndrome etc

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can you tell me what are the causes of chromosomal abnormalities?

are developmental and chromosomal abnormalities same?

what factors are related to maladjustment and crime of youth in our society? please you and all seniors help me....

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Causes are heredity and environment factors like in heredity factors gene mutation, dominant inheritance and sex related chromosomal abnormalities like down;s syndrome
Environmental factors are peer influence, parenting style, socio economic conditions, toilet training

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Chromosomal Abnormalities & Developmental Irregularities

1- Definition:

Chromosome anomaly, abnormality or aberration reflects an atypical number of chromosomes or a structural abnormality in one or more chromosomes.
Chromosome anomalies usually occur when there is an error in cell division following meiosis or mitosis. There are many types of chromosome anomalies. They can be organized into two basic groups, numerical and structural anomalies.

2- Why Do They Occur

Only a small portion of Chromosomal abnormalities is inherited genetically from parents. Most of the Chromosomal abnormalities usually result from an error that occurs
 Either when eggs and sperms are formed (During meiotic division)
 Or during early development stages of fertilized egg. (During mitotic division)

i- Defect before fertilization (Defective meiotic Division)

a- Numerical defect

Before fertilization, an egg or sperm cell may divide incorrectly, resulting in an egg or sperm cell with too many or too few chromosomes. This is called nondisjunction.

Nondisjunction is an error in cell division during production of the gamete cells-the eggs and sperms-by meiosis.
To produce germ cells with 23 chromosomes, cells in the ovary and testes with 46 chromosomes undergo two separate cell divisions called Meiosis I and Meiosis II. In meiosis, a single copy of each of the 23 pairs of chromosomes is randomly distributed to each of the resulting gametes.
Nondisjunction occurs when either homologue fails to separate during anaphase 1 or sister chromatids fail to separate during anaphase II. The result is that one gamete has 2 copies of one chromosome and the other has no copy of that chromosome.
When this cell with the wrong number of chromosomes joins with a normal egg or sperm cell, the resulting embryo has a chromosomal abnormality. A common type of numerical chromosomal abnormality is called a trisomy. This means that an individual has three copies of a specific chromosome, instead of two.
In most cases, an embryo with the wrong number of chromosomes does not survive.

b- Structural defect

Other errors can occur before fertilization. These errors can alter the structure of one or more chromosomes. Individuals with structural chromosomal abnormalities usually have the normal number of chromosomes. However, small pieces of a chromosome (or chromosomes) may be deleted, duplicated, inverted, misplaced or exchanged with part of another chromosome. These structural rearrangements may have no effect on a person if the entire chromosome is there but just rearranged.

ii- Defect after Fertilization (Due to defective Mitotic Division)

Errors in cell division can occur soon after fertilization. This can result in MOSAICISM, a condition in which an individual has cells with different genetic makeups. For example, individuals with the mosaic form of Turner syndrome are missing an X chromosome in some cells. Some individuals with chromosomal Mosaicism may be mildly affected, but the severity of the condition depends largely on the percentage of abnormal cells.

3- Are Chromosomal Abnormalities Inherited

Most chromosomal disorders (such as Down syndrome and Turner syndrome) are not passed from one generation to the next. However there are still few syndromes which pass from parent to offspring

4- Types of Chromosomal Abnormalities

i- Numerical Abnormalities

This is called Aneuploidy (an abnormal number of chromosomes), and occurs when an individual is missing either a chromosome from a pair (monosomy) or has more than two chromosomes of a pair (Trisomy, Tetrasomy, etc.).

a- Down syndrome, also known as Trisomy 21 (an individual with Down syndrome has three copies of chromosome 21, rather than two). Individuals with Down syndrome have varying degrees of intellectual disability, characteristic facial features and, often, heart defects and other problems including short stature

b- (X)- Turner Syndrome (females) is an example of a monosomy where the individual is born with only one sex chromosome, an X. They do not mature sexually during puberty and are sterile. Short stature

c- (XXX)- Triple X: (females) Females has an extra X chromosome. They are taller than average. Most have normal intelligence, though some have learning, behavioral and speech/language problems.

d- (XXY)- Klinefelter syndrome: (boys) Boys with Klinefelter syndrome have two, or occasionally more, X chromosomes along with their Y chromosome. As adults, they produce lower-than-normal amounts of the male hormone testosterone (and often are treated with this hormone) and are infertile.

e- XYY: (boys) one or more extra Y chromosomes. Affected males are sometimes taller than average, have normal sexual development and are fertile. Most have normal intelligence, though some have learning, behavioral and speech/language problems.

f- Trisomy 13: This is also called Patau syndrome. Babies generally have severe mental retardation, serious eye, brain, circulatory defects and many physical birth defects. Most affected babies die before their first birthday.

g- Trisomy 18: This is also called Edwards syndrome. Babies generally have severe mental retardation and many physical birth defects. Most affected babies die before their first birthday.

ii- Structural abnormalities
When the chromosome's structure is altered, this can take several forms:
Deletions: A portion of the chromosome is missing or deleted. Known disorders in humans include

a- Duplications: A portion of the chromosome is duplicated, resulting in extra genetic material.

b- Translocations: When a portion of one chromosome is transferred to another chromosome. There are two main types of translocations. In a reciprocal translocation, segments from two different chromosomes have been exchanged. In a Robertsonian translocation, an entire chromosome has attached to another at the Centromere

c- Inversions: A portion of the chromosome has broken off, turned upside down and reattached, therefore the genetic material is inverted.

d- Rings: A portion of a chromosome has broken off and formed a circle or ring. This can happen with or without loss of genetic material.

e- Isochromosome: An Isochromosome is when one arm of a chromosome is missing, and the other arm is duplicated. A person with 46 chromosomes containing an Isochromosome has a single copy of one arm, and three copies of the other arm.

Wolf-Hirschhorn syndrome is caused by partial deletion of the short arm of chromosome 4. This disorder is characterized by mental retardation, heart defects, poor muscle tone, and seizures

Cat Cry Syndrome (Cry-du-chat syndrome): This is due to partial deletion on chromosome 5.They have severe mental retardation, a small head with unusual facial features, and a cry that sounds like a distressed cat.

Jacobsen syndrome, also called the terminal 11q deletion disorder.

Prader-Willi syndrome: partial deletion on chromosome 15. They have mental retardation, short stature and also may develop extreme obesity

5- Prevention

Only a small portion of chromosomal abnormalities are inherited and these can be screened by testing of parents’ karyotype. This screening can be done using prenatal tests [amniocentesis or chorionic villus sampling (CVS)]. Cells obtained from these tests are grown in the laboratory, and then their chromosomes are examined under a microscope. The lab makes a picture (karyotype) of all the person’s chromosomes, arranged in order from largest to smallest. The karyotype shows the number, size and shape of the chromosomes and helps experts identify any abnormalities. This karyotype, when compared to a normal karyotype, yields the abnormalities
Chromosomal abnormalities account for more than 50% of miscarriages

The chromosomal abnormalities which occur before, during and after fertilization, as the chromosomes divide. These can’t be prevented. However they can be diagnosed as well using above method

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