Chromosomal disorders are caused by abnormalities in chromosomes, including missing or extra chromosomes or parts of chromosomes. Some examples described include Down syndrome, which results from an extra copy of chromosome 21, and Turner syndrome, caused by only one X chromosome. Chromosomal disorders can cause physical and developmental issues, such as intellectual disabilities or medical problems. Gene mutations can also cause disorders like phenylketonuria, which occurs due to the lack of an enzyme, and cystic fibrosis, a genetic disease affecting the lungs and digestive system.

1. CHROMOSOMAL DISORDERS: EASY WAY
TO EXPLAIN MUTATION
CHROMOSOMAL DISORDERS
OBSERVATION
In recent years, we find that a huge number of human disorders like chromosomal disorders, deformities and
diseases become hereditary. Reasons of some diseases are gene mutation and others are gross
chromosomal abnormalities. We can study these abnormal arrangement of chromosome by advanced
genetical studies.
Various genetic disorders are classified into two broad categories
Mendelian disorders and Chromosomal disorders
Here I am trying to elaborate some important chromosomal disorders. The reason of these disorders are
absence or excess or abnormal arrangement of one or more chromosomes.
NAME OF THE
DISORDERS
TYPE OF
DISORDER
RESULT OF
DISORDER
SYMPTOMS OF
DISORDERS
Down’s syndrome
Autosomal
aneuploidy in
chromosomal
disorders
Trisomy of
chromosome 21 in
abnormal
arrangement of
chromosome
Mongolian eyelid fold; ever
open mouth; protruding
tongue; short neck;
projecting lower lip.
Turner’s
syndrome
Sex chromosomal
aneuploidy.
XO sex
chromosomes.
Sterile female
underdeveloped breasts;
short stature; neck with
heavy muscles; loose skin
and narrow hips.
Alkaptonuria
Autosomal gene
mutation.
Lack or inactivity of
enzyme
homogentisate
oxidase.
When the patient releases
urine, it becomes black in
contact with air, cartilage
becomes dark also.
Phenylketonuria
(PKU)
Autosomal gene
mutation.
Lack of enzyme
phenylalanine
hydroxilase.
Extreme mental retardation.
Albinism
Autosomal gene
mutation.
Lack of enzyme
tyrosinase in
chromosomal
disorders
Patient lacks melanin
pigment in skin. Hair, iris
and skin becomes white.
Sickle-cell anemia
Autosomal gene
mutation.
Formation of
hemoglobin in RBCs.
Rupturing of red blood
corpuscles; blocking of
oxygen supply to tissues;
jaundice.
Huntington’s Autosomal gene Production of an Degradation of brain tissue

2. disease mutation (dominant) inhibitor of brain cell
metabolism.
after young age.
Cystic fibrosis Autosomal mutation
Failure of chloride ion
transport.
Mucus clogging in lungs;
abnormalities in liver and
pancreas.
hemophilia
Sex chromosomal
gene mutation or
abnormal
arrangement of
chromosome
Lack of blood
coagulant
Blood does not clot; more
common in males found in
chromosomal disorders.
Red-green color
blindness
Sex chromosomal
gene mutation.
Lack of red and green
color vision pigments
in cone cells of retina.
Patient can not differentiate
red and green color.
Muscular
dystrophy
Sex chromosomal
gene mutation.
Lack of protein
dystrophin.
Muscles degeneration; most
sufferers are males.
Klinfelter’s
syndrome
Sex chromosomal
aneuploidy in
chromosomal
disorders.
XXY sex
chromosome.
Male becomes impotent,
having legs with more
height, obese body with body
hair. Mentally retarded.
QUESTION ON CHROMOSOMAL DISORDERS
Qs1: The linear arrangement of genes on the chromosomes is favored by which event properly? How do
you define this event? Where is it not happening?
Ans1: The phenomenon, that strongly favors the linear arrangement of genes on the chromosome
which is an abnormal arrangement of chromosome, is linkage. Linkage is the tendency for alleles of
different genes to pass together from one generation to the next. The genes located on different
chromosomes cannot show any linkage.
Qs2: How many linkage group are present in an organism whose genomic chromosome number is n=8 in
chromosomal disorder?
Ans2: The number of linkage groups in an organism corresponds to its haploid number of
chromosomes. Therefore, the number of linkage groups in the given organism is 8.
Qs3: Explain why babies born to young women seldom show this abnormality in
chromosomal disorders?
Ans3: The incidence of non disjunction rises to the ovaries of aged women. That is why, women who
are aged, more than year 40 years, they may have tendency to have Down’s syndrome. Women about
40 years age, if becomes pregnant, can have foetal testing for trisomy 21. One in every 600 children
may have Down’s syndrome. Individuals having Down’s syndrome are likely to develop Leukemia
and Alzheimer’s disease.
Qs4: What is familial Down’s syndrome?
Ans4: This familial Down’s syndrome may run in the family. It arises by translocation of a large
segment of or whole of the third chromosome 21 to another chromosome which may term as
abnormal arrangement of chromosome, usually 14. In such cases, the total number of chromosomes
remains normal (46). But there is an extra chromosome 21 material. This is a rare type of Down’s
syndrome. Extra chromosome small in size contains excess genetic information. These
chromosomes interrupt many biological processes.
CONCEPTUAL QUESTION ON CHROMOSOMAL DISORDERS
Qs5: Define super female.

3. Ans5: Super females have genotypes XXX, XXXX, XXXXX with total chromosome number 47, 48, or
49. These females are having underdeveloped sexual characters and they are mentally retarded. If
the number of X is increased then their characteristics become more dangerous.
Qs6: Define super males.
Ans6: Super males have genotype XYY. They have unusual height, mental retardation and perhaps
criminal bent of mind. These people become very much aggressive in nature than normal people.
They use to produce male hormone in excess quantity.
SHORT TYPE ANSWER ON CHROMOSOMAL DISORDERS
Qs7: What are the causes of PKU (phenylketonuria)?
Ans7: The homozygous recessive individual lacks the enzyme phenylalanine hydroxilase . They used
to need to change one amino acid, phenylalanine, to another tyrosine. Phenylalanine accumulates in
the tissues and some of it changes into phenyl pyruvic acid. The later is excreted in the urine.
Accumulation of phenylalanine and metabolites damages the brain and causes the disease. Lack of
the enzyme is due to the abnormal recessive gene. The heterozygous individual is normal, but
carrier.
The affected baby is normal at birth but within a few weeks, phenylalanine level is plasma starts
rising, and by the age of 6 month he develops severe mental retardation. It deficiency of
phenylalanine hydroxylase is detected in the newborn, we can easily prevent this with special diet,
low in phenylalanine.
Qs7: What is muscular dystrophy?
Ans7: Deterioration of muscles at an early age we term as muscular dystrophy. The mutated gene
on X chromosome fails to produce a protein called dystrophin. That protein is thought to relay the
nerve’s signal to the calcium storage sacs in the muscle cell. As a result, calcium is not released.
There is halt for muscular contraction at very first step. Further, the abnormal calcium levels trigger
and release of an enzyme that destroys actin and myosin. The victims becomes invalid by the age of
10 and usually dies by the age of 20.
Qs8: State the special characters about red- green color blindness.
Ans8: Female has two X chromosomes. For a female to be colorblind, it is necessary that each
chromosome has a gene for color blindness. If only one X chromosome bears a gene for color
blindness, its dominant homologous gene on the other X chromosome will check the expression of
the recessive gene. Hence, color blindness occurs more often in the males than in the female.
GENERAL EVENT
A normal woman and color blind man produce normal sons and carrier daughters. A normal man and
a carrier woman produce 50% color blind sons and 50% carrier daughters. A criss-cross inheritance
is noted in this case too. A color blind man and a carrier woman will produce color blind daughter.