KaryotypingNotes and Activity Pages

●Chromosomal mutations…– Additional, missing, or damaged chromosomes

cause several human genetic disorders.– One way of studying these disorders is to

observe the chromosomes themselves.

Why do scientists study chromosomes?

Karyotypes are treated with chemicals that stops cell division at the metaphase stage.

During metaphase, the chromosomes are at the best/longest length for identification.

Karyotyping – tool used to determine the sex of an

individual or detect/identify chromosomal abnormalities.

Humans have 46 chromosomes in every diploid (2n) body cell. The chromosomes of a diploid cell occur in HOMOLOGOUS PAIRS, which are pairs of chromosomes that are similar in size, shape, and the position of their centromere.

The cells are stained, and then placed on glass slides. The chromosomes are observed under the microscope and then photographed. There 2 chromosomes in each place on a karyotypes

• In humans, pairs 1-22 homologous are called AUTOSOMES. Autosomes transmit all genetic traits and conditions.

• Each homologous and alike. (common)

• Pair 23 determines the individual’s sex so that pair is referred to as the SEX CHROMOSOMES.

AND NOWWWWW…We are going to view some Karyotypes and determine if there is a disorder and

what kind of disorder (mutation)

Normal Female Karyotype(XX at pair 23)

Station 1

Normal Male Karyotype (XY at pair 23)

1b

2

Down Syndrome

Down’s Syndrome• Female.• Trisomy 21, extra

chomosome in pair 21.• Down syndrome is one

of the most common chromosomal disorders.

• Physical and mental development is slower.

• Flat facial profile.• Broad forehead.• Thick tongue.• Upward slant to the

eyes.• Short arms and legs.

3

Turner Syndrome

TurnerSyndrome• Females only.• Affects pair 23.• Results from a missing or

incomplete sex chromosome.

• Turner syndrome can cause a variety of problems:• Short stature.• Web neck.• Failure to begin

puberty.• Infertility.• Heart defects.• Learning disabilities.

4

Patau Syndrome

PatauSyndrome• Female.• Trisomy 13; extra

chromosome in pair 13.• Least common and most

severe of the trisomies.• Survival is less than 3

days.• Heart defects.• Incomplete brain

development.• Unusual facial features

such as small or missing eyes, low set ears.

• Extra fingers and toes.• Spinal defects.

5

Klinefelter Syndrome

KlinefelderSyndrome• Males only.• Affects pair 23.• XXY syndrome.• Affects the male

hormonal development due to an extra X chromosome.

• Lack of testosterone can cause less facial and body hair, breast enlargement, and infertility.

• Taller than the average male; longer arms.

• Skinny with wider hips and less muscular structure.

6

Edwards Syndrome

Edward’sSyndrome• Female.• Trisomy 18; extra

chromosome in pair 18.• More than 130

individual defects of the craniofacial structures, brain, heart, kidneys, and gut.

• Small mouth, jaw, and short neck.

• Back of skull is prominent.

• Malformed ears.• Clenched fists with

overlapping fingers; flexed legs and feet.

7

Triple-X Syndrome

Triple-XSyndrome• Female.• Trisomy X; extra X

chromosome at pair 23.• Taller than average.• No unusual physical

features.• Increased risk of learning

disabilities and delayed development of speech and language skills.

• Weak muscle tone.• Behavioral and

emotional difficulties.

8

XYY Syndrome

XYYSyndrome• Males only.• Affects pair 23.• Extra copy of the Y

chromosome.• Taller than average.• Increased risk of

learning disabilities.• Prone to severe acne.• May include antisocial

or behavioral problems.