Transcript Reading a karyogram

Karyotypes
Chromosomes in a cell are visible only when
the cell is dividing
 At metaphase stage chromosomes are fully
condensed and easy to see.
 Metaphase spreads are selected and
photographed in order to analyze
 The chromosomes are then arranged in
homologous pairs.

 The
homologous pairs are placed in order
of descending size. The sex
chromosomes are placed at the end.
A
picture of chromosomes arranged in
this way is known as a karyotype.
A
“normal” human carries 23 PAIRS of
chromosomes (1 set came from the mother, 1
set came from the father)

22 of these sets are called autosomes (or “self
chromosomes”)

1 set are the sex chromosomes


A female carries two X chromosomes (XX)
A male carries an X chromosome and a Y
chromosome (XY)
Mazen Zaharna Molecular Biology 1/2009
 To
label a karyotype correctly, first list the
number of chromosomes found in the
karyotype. Ex. 46
 Secondly, list the type of sex chromosomes
found in the karyotype. Ex. XX
 Lastly, list the any abnormalities at the
appropriate chromosome number.
Normal
Human Female:
Normal
Human Male: 46,
46, XX
XY
 Size
Human chromosomes range in length from 51
million to 245 million base pairs. They are
numbered from largest to smallest
Position of centromere
metacentric
submetacentric
acrocentric
 Banding
pattern
each chromosome has a unique banding
pattern Chromosomal bands are alternating
light and dark segments that result from
various staining procedures.

Numerical



Monosomy
 one member of a chromosome pair is missing
Trisomy
 one chromosome set consists of 3 copies of a
chromosome
Structural
-Translocations
-Inversions
-Deletions
-Duplications
Mazen Zaharna Molecular Biology 1/2009
Translocation
Deletion
Derivative
chromosome
Inversion
Insertion
Isochromosome
Ring
chromosome
47,XY+5(Del)9