What is a chromosome? A chromosome is… A very long DNA molecule and associated proteins that carries portions of the hereditary information of an organism. They are composed of DNA and proteins that are located within the nucleus of our cells. Chromosomes determine everything from hair color and eye color to sex.
Chromosomes are describedwith the following categories: Metacentric centromere is median or near median chromosome has two well defined arms with a length ratio varying from 1:1 to 2.5:1 Submetacentric A chromosome whose centromere lies between its middle and its end but closer to the middle.
Chromosomes are describedwith the followingcategories: Acrocentric centromere is close to one end of the chromosome one arm is substantially smaller than the other and the arm ratio ranges from 3:1 to 10:1 Telocentric centromere is a strictly terminal entity and the chromosome is one armed
Chromosomes are describedwith the followingcategories:
Chromosomes are alwaysarranged with the short armon top: Short arm is labeled P (French for petit) Long arm is labeled Q
Human chromosomes aredivided into 7 groups & sexchromosomes A 1-3 Large metacentric 1,2 or submetacentric B 4,5 Large submetacentric, all similar C 6-12, X Medium sized, submetacentric - difficult D 13-15 medium-sized acrocentric plus satellites E 16-18 short metacentric 16 or submetacentric 17,18 F 19-20 Short metacentrics G 21,22,Y Short acrocentrics with satellites. Y no satellites.
Karyotype An individuals collection of chromosomes. It refers to the complement of chromosomes either at the species level, or of individuals. Is used to look for abnormal numbers or structures of chromosomes.
Karyotyping Also known as Karyotype Test A laboratory technique that produces an image of an individuals chromosomes. Is a test to identify and evaluate the size, shape, and number of chromosomes in a sample of body cells. Extra, missing, or abnormal positions of chromosome pieces can cause problems with a persons growth, development, and body functions.
Why Karyotyping isdone: Determine whether the chromosomes of an adult have an abnormality that can be passed on to a child. Determine whether a chromosome defect is preventing a woman from becoming pregnant or causing miscarriages. Determine whether a chromosome defect is present in a fetus.
Why Karyotyping isdone: Determine whether chromosomal problems may have caused a fetus to be stillborn. Determine the cause of a babys birth defects or disability. Help determine the appropriate treatment for some types of cancer. Identify the sex of a person by determining the presence of the Y chromosome. This may be done when a newborns sex is not clear.
ChromosomalAberrations Sex chromosome abnormalities occur as a result of chromosome mutations brought on by mutagens (like radiation) or problems that occur during meiosis. One type of mutation is caused by chromosome breakage. The broken chromosome fragment may be deleted, duplicated, inverted, or translocated to a non-homologous chromosome. Another type of mutation occurs during meiosis and causes cells to have either too many or not enough chromosomes.
Klinefelter Syndrome(XXY) syndrome, also known as the XXY Klinefelter condition, is a term used to describe males who have an extra X chromosome in most of their cells. Instead of having the usual XY chromosome pattern that most males have, these men have an XXY pattern. Klinefelter syndrome is named after Dr. Henry Klinefelter, who first described a group of symptoms found in some men with the extra X chromosome. Scientists believe the XXY condition is one of the most common chromosome abnormalities in humans. About one of every 500 males has an extra X chromosome, but many don’t have any symptoms.
Klinefelter Syndrome(XXY) Common Physical Characteristics: small testicles and penis Breast enlargement sterility infertile
Metafemale (XXX) A metafemale is a woman who has an extra X chromosome. It is a condition that is commonly referred to as Triple X Syndrome and it is thought to affect around 1 in every 1000 women. Triple X Syndrome results during division of a parents reproductive cells. In most cases there will be no unusual physical features or medical problems resulting from Triple X Syndrome. This is because in all female cells there is only one active X chromosome at any one time.
Metafemale (XXX) Common Physical Characteristics: Generally normal due to Barr Bodies Tall stature Behavioral problems Clumsiness and poor co-ordination Wide-set eyes Reduced muscle tone Ovarian failure
Turner Syndrome (XO) Turner syndrome is a chromosomal condition that alters development in females. This condition occurs in about 1 in 2,500 female births worldwide, but is much more common among pregnancies that do not survive to term (miscarriages and stillbirths). Turner syndrome is a chromosomal condition related to the X chromosome Researchers have not yet determined which genes on the X chromosome are responsible for most signs and symptoms of Turner syndrome.
Turner Syndrome (XO) Common Physical Characteristics: extra skin on the neck (webbed neck) puffiness or swelling (lymphedema) of the hands and feet skeletal abnormalities heart defects kidney problems
Jacobs Syndrome (XYY) Jacobs syndrome is a rare chromosomal disorder that affects males. It is caused by the presence of an extra Y chromosome. Males normally have one X and one Y chromosome. However, individuals with Jacobs syndrome have one X and two Y chromosome. Males with Jacobs syndrome, also called XYY males. Jacobs syndrome occurs when a male inherits two Y chromosomes from his father instead of one. He is an XYY male. Most males are XY. The exact cause of the XYY aberration is unknown.
Jacobs Syndrome (XYY) Common Physical Characteristics: With uncontrolled temper and antisocial Severe acne problems Tall and thin High testosterone levels
Autosomal Aberrations Syndrome or disorder of interest is pertaining to a chromosome that is NOT a sex chromosome, either X or Y but of body chromosomes.
Down Syndrome(Trisomy 21) Down syndrome (also called Trisomy 21) is a genetic disorder that occurs in approximately 1 of 800 live births. Down syndrome is named after Doctor Langdon Down, who in 1866 first described the syndrome as a disorder. It is the leading cause of cognitive impairment.
Down Syndrome(Trisomy 21) Common Physical Characteristics: Oblique eye features mild to moderate learning disabilities Developmental delays Characteristic facial features, Low muscle tone in early infancy. Epicanthal fold Simian crease
Edward Syndrome(Trisomy 18) The Edwards syndrome, which got its name after the famous doctor, Dr. John Edward. A genetic chromosomal disorder caused by an error in cell division resulting on additional third chromosome 18. Edwards syndrome, a result of one of the genetic disorders and most common after Down syndrome, occurs in approximately one among 3000 to 6000 births.
Edward Syndrome(Trisomy 18) Common Physical Characteristics: Upturned nose Growth Deficiency Abnormal skull shape and facial features Clenched hands Rocker bottom feet Cardiac and renal abnormalities
Patau Syndrome(Trisomy 13) Patau syndrome, also referred to as, Trisomy 13. A form of genetic disorder in which all or a portion of the persons chromosome thirteen appears three times instead of twice in the cells of their body. The extra material interferes with the persons regular process of development, which leads to severe intellectual disability and physical abnormalities in a number of parts of their body.
Patau Syndrome(Trisomy 13) Common Physical Characteristics: Polydactyl and cleft palate Low-set ears Scalp defects Clenched hands Small lower jaw Mental retardation Single palmar crease Undescended testicle Skeletal abnormalities Close-set eyes - eyes may actually fuse together
Angelman Syndrome A neuro-genetic disorder that it is usually caused by deletion or inactivation of genes on the maternally inherited chromosome 15 while the paternal copy, which may be of normal sequence, is imprinted and therefore silenced. AS is named after a British pediatrician, Dr. Harry Angelman, who first described the syndrome in 1965. People with AS are sometimes known as "angels", both because of the syndromes name and because of their youthful, happy appearance.
Angelman Syndrome Common Physical Characteristics: Intellectual and developmental delay Sleep disturbance Seizures Jerky movements (especially hand-flapping) Frequent laughter or smiling Usually a happy demeanor.
Angelman SyndromeNote: The deletion inChromosome 15 is so smalland is almost not visible
Prader–Willi syndrome Is a rare genetic disorder in which seven genes (or some subset thereof) on chromosome 15 (q 11–13) are deleted or unexpressed (chromosome 15q partial deletion) on the paternal chromosome. It was first described in 1956 by Andrea Prader (1919–2001), Heinrich Willi (1900–1971), Alexis Labhart (1916), Andrew Ziegler, and Guido Fanconi of Switzerland.
Prader–Willi syndrome Common Physical Characteristics: Low muscle tone Short stature Incomplete sexual development Cognitive disabilities Problem behaviors Chronic feeling of hunger that can lead to excessive eating and life-threatening obesity
Structural Aberrations Deletions A portion of the chromosome is missing or deleted. Known disorders in humans include Wolf- Hirschhorn syndrome, which is caused by partial deletion of the short arm of chromosome 4; and Jacobsen syndrome, also called the terminal 11q deletion disorder. Duplications A portion of the chromosome is duplicated, resulting in extra genetic material. Known human disorders include Charcot-Marie-Tooth disease type 1A which may be caused by duplication of the gene encoding peripheral myelin protein 22 (PMP22) on chromosome 17.
Structural Aberrations 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 - in humans these only occur with chromosomes 13, 14, 15, 21 and 22. Inversions A portion of the chromosome has broken off, turned upside down and reattached, therefore the genetic material is inverted.
Structural Aberrations Insertions A portion of one chromosome has been removed from its normal place and inserted into another chromosome. 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. Isochromosome Formed by the mirror image copy of a chromosome segment including the centromere.
Wolf-HirschhornSyndrome A syndrome is due to a specific chromosomal deletion which is the cause of typical facial features and developmental delays. The anomalies are due to the lack of chromosomal material from the top of one of the number 4 chromosomes. This results in missing genes which account for the anomalies. The degree of deletions and scope of symptoms vary widely and reflect the amount of genetic material that is missing.
Wolf-HirschhornSyndrome Common Physical Characteristics: Short philtrum Small head size (microcephaly) "Greek helmet like" nose shape Wide spaced eyes (hypertelorism) Mental retardation
Cri-du-chat Syndrome Also known as chromosome 5p deletion syndrome, 5p minus syndrome or Lejeune’s syndrome A rare genetic disorder due to a missing part of chromosome 5. Its name is a French term (cat- cry or call of the cat) referring to the characteristic cat-like cry of affected children. It was first described by Jérôme Lejeune in 1963. The condition affects an estimated 1 in 50,000 live births, strikes all ethnicities, and is more common in females by a 4:3 ratio.
Cri-du-chat Syndrome Common Physical Characteristics: Excessive drooling Feeding problems because of difficulty swallowing and sucking. Low birth weight and poor growth Severe cognitive, speech, and motor delays Behavioral problems such as hyperactivity, aggression, tantrums, and repetitive movements. Unusual facial features which may change over time
Cat eye Syndrome A rare condition caused by the short arm (p) and a small section of the long arm (q) of human Chromosome 22 being present three (trisomic) or four times (tetrasomic) instead of the usual two times. The term "Cat Eye" syndrome was coined because of the particular appearance of the vertical colobomas in the eyes of some patients. However, over half of the CES patients in the literature do not present with this trait. There is no significant reduction in life expectancy in patients who are not afflicted with one of CES life threatening abnormalities.
Cat eye Syndrome Common Physical Characteristics: Iris coloboma Anal atresia (abnormal obstruction of the anus) Unilateral or bilateral iris coloboma (absence of tissue from the colored part of the eyes) Palpebral fissures (downward slanting openings between the upper and lower eyelids) Preauricular pits/tags (small depressions/growths of skin on the outer ears) Cardiac defects (such as TAPVR) Kidney problems (missing, extra, or underdeveloped kidneys) Short stature Scoliosis/Skeletal problems
Velo-Cardio-FacialSyndrome Velocardiofacial syndrome is a genetic disorder that is present from birth and can be characterized by a variety (over thirty) different signs and symptoms. Although the gene or genes that cause velocardiofacial syndrome have not been identified, most of the children who have been diagnosed with this syndrome are missing a small part of chromosome 22.
Velo-Cardio-FacialSyndrome Common Physical Characteristics: cleft palate (opening in the roof of the mouth) heart defects, certain facial features minor learning problems speech and feeding problems
Charcot-Marie-ToothDisease Also known also as Morbus Charcot-Marie- Tooth, Charcot-Marie-Tooth neuropathy, hereditary motor and sensory neuropathy (HMSN), hereditary sensorimotor neuropathy (HSMN), or peroneal muscular atrophy. An inherited disorder of nerves (neuropathy) that takes different forms. It is caused by duplication of the gene encoding peripheral myelin protein 22 (PMP22) on chromosome 17.
Charcot-Marie-ToothDisease Common Physical Characteristics: Foot drop which is the dropping of the forefoot due to weakness, damage to the peroneal nerve or paralysis of the muscles in the anterior portion of the lower leg. Scoliosis Malformed hip sockets Gastrointestinal problems can be part of CMT, as can chewing, swallowing, and speaking (as vocal cords atrophy).