Cytogenetics - study of chromosomes, karyotypes

TASK 1: Structure of polytene (giant) chromosome

PP: polytene (giant) chromosome - "obrovské chromosomy", NP: salivary gland of chironomid larva (Chironomus sp.) or Drosophila melanogaster

Prepare salivary glands of the chironomid larva and control the presence of the giant chromosomes under a microscope. Pass the slide (sample-side up) through the flame of the burner 3 to 4 times to heat-fix the sample. Stain it with acetorcein for 5-10 min. Cover with a cover glass and prepare the compression sample. Observe polytene chromosomes with chromomeres (stripes of different width) and puffs.


Fig.: Polytene chromosome in cells of salivary gland in chironomid larva.

TASK 2: Sex chromatin in somatic cells

NP and PP: buccal smear - "pohlavní chromatin"

Take a sample from the inner side of the cheek using a cotton swab and impress the swab on a slide. Fix it above the flame and apply acetorcein on the slide for 5 min. and then cover with a cover glass. In somatic cells of female buccal mucosa, you can find sex chromatin (Barr body), a densely colored body in the periphery of the nucleus.


Fig.: Sex chromatin.

TASK 3: Mammal karyotype

PP: karyotype of rabbit, pig, sheep, horse, cattle and human - "karyotyp králík, prase, ovce, kůň, skot, člověk".

Observe permanent samples prepared from lymphocytes of different domestic animals or human (Note: In the samples, you can find round nucleus of lymphocytes and clusters of chromosomes = karyotype). Compare the numbers and types of chromosomes (rabbit 2n = 44, pig 2n = 38, sheep 2n = 54, horse 2n = 64 and human 2n = 46).

TASK 4: Karyotype of onion

NP: the rootlet of onion (Allium cepa) cultivated with 0.02 % water solution of colchicin and stained with acetorcein.

Prepare the compression sample from a stained onion rootlet and find the cluster of chromosomes (karyotype).


Fig.: Examples of karyotype: A – in cattle (Bos taurus), B – in onion (Allium cepa).

TASK 5: Karyotype records

Write following karyotypes:

  1. karyotype of healthy man and woman
  2. karyotype of bull (male cattle), mare (female horse), ram (male sheep)
  3. karyotype of man with Down syndrome and man with Klinefelter syndrome
  4. karyotype of woman with Edwards syndrome and woman with Turner syndrome