Karyotypes
SBI3U@RHSA
Key terminology
 A karyotype is a picture of the particular




set of chromosomes that an individual
has.
A karyotype can be used to diagnose
specific genetic disorders.
Gene - part of a chromosome that
controls the expression of a particular
trait.
Allele - is a variation of a gene
Examples of hair colour alleles include
black, brown, blond and red.
Alleles on Homologous Chromosomes
•The gene for hair colour has 4
alleles and this person inherited a
blond allele and a brown allele
•Homologous chromosomes
pairs of chromosomes that are
identical in their length,
centromere location and banding
pattern.
•Alleles are always found on the
same gene of homologous
chromosomes.
Karyotype – Somatic Cell Example 1
-Found in somatic cells during
the beginning of interphase
-Chromosomes are diploid
and unreplicated (single
stranded)
-The first 22 pairs of
homologous chromosomes
are called autosomes
-The 23rd pair of
chromosomes are the sex
chromosomes
-The sex chromosomes are
only homologous in females
Karyotype – Somatic Cells Example 2
-These chromosomes are
diploid and replicated
(double stranded)
-This occurs in somatic
cells during prophase
-Also found in the
precursor cells required to
make gametes in the
testes (spermatogonium)
and ovary (oogonium)
Karyotype of a gamete (sex cell)
 Chromosomes are haploid
and unreplicated (single
stranded)
 After fertilization occurs the
zygote will have a diploid
number of chromosomes
Summary
Haploid,
unreplicated
(n)
Diploid,
Replicated
(4n)
Diploid,
unreplicated
(2n)
What is n?
- n indicates the number of
haploid chromosomes in a
organism
- Fruit flies have n=4
- A dove has n = 39
Karyotype Charts
• A karyotype is an organized profile of a person's
chromosomes.
• Chromosomes are arranged and numbered by size, from
largest to smallest.
• This arrangement helps scientists quickly identify
chromosomal alterations that may result in a genetic
disorder.
• To make a karyotype, scientists take a picture of
someone's chromosomes, cut them out and match them
up using size, banding pattern and centromere
position as guides.
Now you try your hand:
http://www.biology.arizona.edu/human_bio/activities/karyotyping/karyotyping.html