Karyotypes

What is a karyotype?

Photomicrograph of a dividing cells chromosomes

What is a karyotype used for?

Used to identify chromosomal abnormalities

How many chromosomes are in humans?

44 autosomes and 2 sex chromosomes

When was the correct number of human chromosomes established?

Not until 1956 due to the clumping of chromosomes in dead tissue

How are chromosomes paired and grouped?

Paired with homologue and grouped according to length and location of centromere

Preparation of a karyotype part 1

Acquire white blood cells

Preparation of a karyotype part 2

Add chemical (colchicine) to break down spindle fibers which effectively halts all cells at metaphase and kills them

Preparation of karyotype part 3

Add distilled water and centrifuge to separate white blood crlls

Preparation of karyotype part 4

Fix with alcohol and stain

Preparation of karyotype part 5

Photograph burst cells using microscope (ones in metaphase) and then enlarge

Preparation of karyotype part 6

Cut out chromosomes and match pairs

Preparation of karyotype part 7

Sort by decreasing soze

Who is this tool (the karyotype) used by?

Genetic counsellors and cytogeneticists

Where is the karyotype used extensively?

In the HGS (Human Genome Study)

What type of chromosomal abnormalities can be detected by using a karyotype?

Sex cells with abnormal number of chromosomes due to nondisjunction (usually causes embryos that are not viable)

Down Syndrome

Usually an extra chromosome in chromosome pair 21. Sometimes can be caused by translocation of chromosome 21-14

Symptoms of Down Syndrome

Mild to severe retardation, flat face, thick tongue & neck, abnormalities of organs, generally early death.

Klinefelter's Syndrome

Extra X Chromosome

Symptoms of Klinefelter's Syndrome

Small breasts, reduced fertility, and long limbs, male

Examples of chromosomal abnormalities

Can also have XXXY and XXXXY

XXX and X (Turner's Syndrome)

Generally normal females with reduced fertility

Deletion

Small pieces of chromosome get deleted during Interphase. Usually lethal.

Duplication

Pieces of chromosome that got deleted are incorporated into its homologue, essentially duplicating that potion of the chromosome

Translocation

Small pieces of chromosome are deleted form one chromosome &I moved to another non-homologus chromosome

Inversion

Small piece of chromosome "flips" in place