Karyotypes

What is a karyotype? A karyotype is made from a picture of the nucleus of a cell which has begun to undergo mitosis. Mitosis is the process by which our body cells divide to make new cells. At this stage in the cell cycle, the chromosomes are clearly visible.

What are they used for? Karyotypes are typically used on fetal cells to determine: –The sex of the child –If there are any chromosomal abnormalities. –The cells used to perform the karyotype are collected from the amniotic fluid.

What does a karyotype look like?

How are chromosomes identified? There are three characteristics used by scientist to match up the chromosomes. Size Position of the centromere Banding pattern The chromosome are numbered in order of descending length (1 is the longest)

How do male and female karyotypes differ? They differ in the 23rd pair of chromosomes which determines gender. If there are 2 X chromosomes, the child is female. If there is 1 X and 1 Y, the child is male. The X chromosome is much larger than the y chromosome and carries more genetic information.

Normal Female Karyotype

Normal Male Karyotype

Chromosomal Mutations In addition to determing the gender of a fetus, a Karyotype can help to identify diseases. During normal meiotic cell division the sperm and egg cells normally get a full set of 46 chromosomes. Sometimes however the division is unequal, and the resulting sex cells have either too many or too few chromosomes.

Trisomy A trisomy is the condition in which a cell has an extra copy of a chromosome. Instead of having two copies of a chromosome, they have three. A common example of a trisomy occurs at chromosome 21. Trisomy 21 is commonly known as Down syndrome.

Trisomy 21

Down syndrome This disease was named after the doctor who characterized the symptoms. It wasn’t until many years later did scientists discover the cause of the disease. Symptoms include mild to severe mental retardation, charactictics facial features, and small stature. Most people with Down syndrome are now able to live semi-independent lives due to increased understanding and treatment.

Another trisomy

Trisomy 18 This condition is known as Edwards Syndrome. In this case, the patient was male. A trisomy can occur at any chromosome and in most cases results in a miscarriage. In many cases, the woman never even knows she was pregnant.

Klinefelter’s syndrome karyotype

Klinefelter’s syndrome In this condition, the egg cell involved in fertilization contained not one, but two copies of the X chromosome. In many cases it is undiagnosed. Males with this condition are unable to reproduce.

Karyotype, 47, XXX

47, XXX Females with this disorder inherited an extra copy of the X chromosome. In some cases the woman may suffer from mild learning difficulties, but usually this condition goes unrecognized. There have been cases in which some women have 4 or 5 copies of the X chromosome.

Monosomy A monosomy occurs when a person receives only one copy of a chromosome instead of the normal two. In some cases only part of a chromosome is missing.

Turner’s syndrome

Females with this condition only received one X chromosome instead of two. They tend to be shorter of stature and are incapable of reproducing.

Monosomy 5

Cru du chat syndrome This condition results from a partial monosomy of chromosome 5. Only part of a chromosome is missing. Disease gets name from the characteristic sound made by infants with this disease. They sound like kittens due to altered shape of their larynx.

Practice karyotype What type of chromosomal mutation is present? Can you determine anything else about this patient?

Practice karyotype 2 Can you identify what is wrong? Can you determine anything else from this karyotype?

Practice karyotype 3 What is the disorder present in this karyotype? What can you determine?