Karyotype

A chart of chromosome pairs arranged by length and

location of the centromere

How are karyotypes made?

• Somatic cells (remember these are body cells) in metaphase are grown and then dropped onto a slide bursting the nucleus.

• The chromosomes are photographed, paired up and arranged by size.

Karyotype

Normal Human Karyotype

Sex Chromosomes

• The sex of the individual can be determined by examining the sex chromosomes.

• XX is a female• XY is a male

Karyotype Notation

• 1. List the total number of chromosomes (46 is normal for humans)

• 2. List the sex chromosomes. • 3. List any extra or missing

chromosomes

What is the sex of this individual?

Notation: 46XY

XY = male

And this one?Klinefelter syndrome

Notation: 47 XXY

Klinefelter syndrome

• Klinefelter's syndrome is a condition that occurs in men who have an extra X chromosome in most of their cells. The most common symptom is infertility.

• 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.

Karyotypes

• Karyotypes are used to identify defects in the chromosomes like:

• Missing chromosomes• Multiple chromosomes

Do you see a problem?Trisomy 21

Notation: 47 XY +21

Trisomy

• Trisomy: 3 copies of one chromosome instead of the normal 2.

• Nondisjunction: (junction means joined) a chromosome pair fails to separate during meiosis

• One cell ends up with 3 copies of a chromosome

Trisomy 21 or Down Syndrome

• Down syndrome (DS), also called Trisomy 21, is a condition in which extra genetic material causes delays in the way a child develops, both mentally and physically. It affects about 1 in every 800 babies.

• The physical features and medical problems associated with Down syndrome can vary widely from child to child. While some kids with DS need a lot of medical attention, others lead healthy lives.

Trisomy 21 or Down Syndrome

Where is the trisomy?Edwards syndrome

Notation: 47 XY +18

Edward Syndrome

• Trisomy 18 (also known as Trisomy E or Edward's Syndrome) is a genetic disorder caused by the presence of all or part of an extra 18th chromosome. It is named after John H. Edwards, who first described the syndrome in 1960. It is the second most common autosomal trisomy, after Down Syndrome, that carries to term.

• The incidence of the syndrome is estimated as one in 3,000 live births. The survival rate of Edwards Syndrome is very low. About 95% die in utero. Of liveborn infants, only 50% live to 2 months, and only 5–10% will survive their first year of life.

Edward Syndrome

What’s wrong?Patau syndrome

Notation: 47 XX +13

Patau syndrome• Patau syndrome, is a chromosomal abnormality, in

which a patient has an additional chromosome 13 due to a nondisjunction of chromosomes during meiosis. The extra chromosome 13 disrupts the normal course of development, causing heart and kidney defects. Like all nondisjunction conditions (such as Down syndrome and Edwards syndrome), the risk of this syndrome in the offspring increases with maternal age at pregnancy. Patau syndrome affects approximately one in 25,000 live births.

• Median survival age for children with Patau syndrome is 2.5 days, with only one in 20 children surviving longer than 6 months. However, some children survive into their teens and seem to fare better than might be expected based on reports from those who die in the perinatal period. Reports of adults with Patau syndrome are rare.

Patau syndrome

Karyotypes

• Geneticist can also see problems within individual chromosomes like deletions and additions.

Cri-du-chatDeletion in #5

Cri-du-chat• Cri du chat syndrome, also known as

chromosome 5p deletion syndrome, is 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.

• The condition affects an estimated 1 in 20,000 to 50,000 live births, strikes all ethnicities, and is more common in females by a 4:3 ratio

• The syndrome gets its name from the characteristic cry of affected infants, which is similar to that of a meowing kitten, due to problems with the larynx and nervous system

Cri-du-chatOther symptoms

Cleft Palate

Syndactyly

Microcephaly