Chromosomes. Levels of chromatin organization. Human karyotype and its medical importance

1.

PRACTICAL CLASS №4
CHROMOSOMES. LEVELS OF CHROMATIN
ORGANIZATION. HUMAN KARYOTYPE AND ITS
MEDICAL IMPORTANCE.

2.

MORPHOLOGY OF CHROMOSOMES: CHROMOSOMES ARE THE ROD-SHAPED
,FILAMENTOUS BODIES PRESENT IN THE NUCLEUS, WHICH BECOME VISIBLE
DURING CELL DIVISION. THEY ARE CARRIERS OF THE GENE OR UNIT OF
HEREDITY.

3.

HOMOLOGOUS CHROMOSOMES ARE CHROMOSOMES THAT SHARE:
THE SAME STRUCTURAL FEATURES (E.G. SAME SIZE, SAME BANDING PATTERNS,
SAME CENTROMERE POSITIONS)
THE SAME GENES AT THE SAME LOCI POSITIONS (WHILE THE GENES ARE THE
SAME, ALLELES MAY BE DIFFERENT)

4.

DIPLOID IS A CELL OR ORGANISM THAT HAS PAIRED CHROMOSOMES, ONE FROM EACH PARENT.
IN HUMANS, CELLS OTHER THAN HUMAN SEX CELLS, ARE DIPLOID AND HAVE 23 PAIRS OF
CHROMOSOMES. HUMAN SEX CELLS (EGG AND SPERM CELLS) CONTAIN A SINGLE SET OF
CHROMOSOMES AND ARE KNOWN AS HAPLOID.

5.

AN AUTOSOME IS ANY OF THE NUMBERED CHROMOSOMES, AS OPPOSED TO
THE SEX CHROMOSOMES. HUMANS HAVE 22 PAIRS OF AUTOSOMES AND ONE
PAIR OF SEX CHROMOSOMES (THE X AND Y). AUTOSOMES ARE NUMBERED
ROUGHLY IN RELATION TO THEIR SIZES.

6.

EACH CHROMOSOME IN ITS NON-REPLICATED STATE CONSISTS OF A SINGLE
CHROMATID, WHICH IS SIMPLY A VERY LONG DNA MOLECULE TO WHICH ARE
ATTACHED A GREAT MANY HISTONE PROTEIN MOLECULE COMPLEXES.

7.

CENTROMERES WERE FIRST DESCRIBED BY WALTHER FLEMMING IN 1882. ALTHOUGH
THE WORD “CENTROMERE” IS DERIVED FROM THE GREEK WORDS “CENTRO” (CENTRAL)
AND “MERE” (PART), CENTROMERES ARE NOT ALWAYS FOUND IN THE CENTER OF
CHROMOSOMES.

8.

THE CHEMICAL COMPOSITION OF A CHROMOSOME IS DNA AND HISTONE PROTEINS.
THE DNA MOLECULES ARE VERY LONG, YET THEY ARE PACKED WITH THE HELP OF
POSITIVELY CHARGED HISTONES INTO A SMALLER DIAMETER. HISTONES ARE RICH IN
ARGININE AND LYSINE (AMINO ACID RESIDUES), WHICH FORM THE CORE AROUND
WHICH A DOUBLE-STRANDED DNA FRAGMENT IS WOUNDED.

9.

POLYTENE CHROMOSOMES ARE LARGE CHROMOSOMES WHICH HAVE
THOUSANDS OF DNA STRANDS. THEY PROVIDE A HIGH LEVEL OF FUNCTION IN
CERTAIN TISSUES SUCH AS SALIVARY GLANDS OF INSECTS.

10.

THE 22 AUTOSOMES ARE NUMBERED BY SIZE. THE OTHER TWO CHROMOSOMES,
X AND Y, ARE THE SEX CHROMOSOMES. THIS PICTURE OF THE HUMAN
CHROMOSOMES LINED UP IN PAIRS IS CALLED A KARYOTYPE.

11.

THE TERM KARYOTYPE REFERS TO A DISPLAY OF THE CHROMOSOMES OF A CELL
BY LINING THEM UP, BEGINNING WITH THE LARGEST CHROMOSOME AND WITH
THE SHORT ARM ORIENTED TOWARD THE TOP.

12.

A CONDENSED MASS OF CHROMATIN THAT IS OBSERVED IN THE NUCLEUS OF NONDIVIDING SOMATIC CELLS OF FEMALES. IT IS NOT
OBSERVED IN THE SOMATIC CELLS OF NORMAL MALES. THE SUBSTANCE REPRESENTS MATERIAL WITHIN THE X CHROMOSOME THAT IS NOT
INVOLVED IN SOMATIC-CELL METABOLISM. THE PRESENCE OF SEX CHROMATIN IN SOMATIC CELLS IS GENERALLY REGARDED AS PROOF OF
THE SEXUAL IDENTITY OF FEMALES. ALSO CALLED BARR BODY.

13.

THANK YOU FOR YOUR ATTENTION!