Karyotypes
Different organisms have different numbers of chromosomes
• Autosomes: Any
chromosome that is not
a sex chromosome (X or
Y chromosome)
– Humans have 22 pairs of
autosomes
• Karyotype: a
photograph of the
complete diploid set of
chromosomes grouped
in homologous pairs and
arranged in order of
decreasing size.
Karyotypes
How to make a karyotype:
1. Photograph a cell going through
mitosis.
– Why couldn’t you photograph a
cell during interphase to make a
karyotype?
2. Match up the chromosomes in
homologous pairs.
– What do a pair of homologous
chromosomes have in common?
– How are the chromosomes in a
homologous pair different?
3. Arrange the chromosomes from
largest to smallest
Karyotypes
• What can be learned from making a karyotype?
– The number of
chromosomes in the
organism
– The gender
– The presence of
chromosomal disorders
• What does the karyotype
to the right tell you about
the organism?
Chromosomal Disorders
• Chromosomal mutation: mutation
that changes the number or
structure of chromosomes (entire
genes not just bases are changed).
– Deletion: The loss of all or part
of a chromosome
– Duplication: A segment of the
chromosome is repeated
– Inversion: part of the
chromosome is reverse from its
usual direction.
– Translocation: one chromosome
breaks off and attaches to
another chromosome.
Chromosomal Disorders
Many chromosomal disorders are
caused by a mistake in meiosis
called nondisjunction.
• Nondisjunction: homologous
chromosomes fail to separate
during meiosis
– Abnormal number of
chromosomes find their way
into gametes
– Causes chromosomal
disorders.
– Which of the sperm cells have
an extra chromosome, which
are missing a chromosome?
Chromosomal Disorders
Disorders caused by
nondisjunction.
Down Syndrome
• Caused by an extra 21st
chromosome.
• Also known as trisomy 21
• Trisomy: having three
copies of a chromosome.
Chromosomal Disorders
Turner’s Syndrome
• Females are born with only one
X chromosome
• Monosomy X: having only one
X chromosome.
Klinefelter’s Syndrome
• Males born with two X
chromosomes and a Y
chromosome.
• Y chromosome determines if
the individual is male or female.