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Karyotypes
What are they??
How do we use them?
Normal Karyotype--male
Normal Karyotype--female
Is this person female or male?
How are DNA samples obtained for
karyotypes?
What to look for?

Are there 46 chromosomes?

Are there 2 identical pairs of each
autosome and 2 sex chromosomes?

Are there any rearrangements between
chromosomes or large deletions?
Trisomy 21 or Down Syndrome
1 in 700 births
47 chromosomes
XY or XX
#21 Trisomy
Nondisjunction
3
Correlation between mother’s age
and Trisomy 21 incidence
Turners syndrome
caused by
Nondisjunction
Monosomy
Male or Female?
Is this a normal karyotype??
XXY Male (Extra X)
Klinefelter syndrome
XXY on 23rd pair
 Male with some female characteristics
 small testes that do not produce as much
testosterone as usual
 Delayed puberty
 Reduced body hair
 infertility

Deletion—18 Q Deletion Syndrome
If there are chromosomal number
abnormalities, how do they form?

Meiosis: the process of creating sperm or
egg from a diploid cell

If there is a mistake when chromosomes
are separating, then the resulting sperm
or egg will have too many or too few
chromosomes.
Nondisjunction
What we can’t see

Individual DNA strands or genes

The number of genes in any given area of
a chromosome.

The presence or location of small
mutations. (Scientists cannot predict
diseases caused by small mutations within
genes.
Other chromosomal
disorders that can
arise?
Problems with chromosomes

Duplication: copied parts of chromosome
A
A
B
B
C
B
D
B
C
D
Problems with chromosomes

Deletion: missing parts of chromosome
A
A
B
D
C
D
Problems with chromosomes

Inversion: parts of chromosome tched
A
A
B
C
C
B
D
D
Chromosomal mutations
Deletion
Duplication
Inversion
Translocation
Human genetic disorders from
deleterious genes

Sometimes the alleles inherited contribute to
disorders and not from the number or shape of
the chromosomes.
Sex-linked: genes found on X or Y
chromosome
2. Recessive: requires 2 allele copies to express
disorder
3. Dominant: requires only 1 allele copy to
express disorder
1.
Recessive disorders
Dominant disorder