A genetic disorder is caused by a mutation to a
gene, group of genes, or entire chromosome.
Remember, genes carry instructions to build proteins.
When these instructions are mutated, proteins can’t
get build correctly.
Genetic disorders generally occur in two different
a) Chromosomal defect (chromosomal mutations)
b) Gene defect (gene mutations)
Gene defects occur when an individual gene is
mutated on a chromosome.
Since only one gene is affected, usually only one
protein is affected. Ex.) hemophilia
Many gene defects can be inherited, however, many of
them can occur spontaneously (without being
inherited) through being exposed to mutagens like
chemicals or radiation.
Inheriting a Gene Defect
There are generally three different patterns of
a) Autosomal recessive
b) Autosomal dominant
c) Sex linked recessive
Autosomal Recessive Inheritance
Ex.) Cystic Fibrosis
Caused by a recessive allele on chromosome #7.
FF – normal Ff – carrier (normal) ff – disease
Two parents that are both carriers for CF, want to know
the chance of having a child with CF?
Autosomal Dominant Inheritance
Ex.) Huntington’s Disease
Caused by a dominant allele on chromosome #12.
HH – lethal in embryo
Hh – Huntington’s disease
hh – normal
One member of a couple has Huntington’s, what is the chance of
their children having the disease?
Sex Linked Recessive Inheritance
Caused by recessive allele on the X chromosome
XHXH - Normal female
XHXh - Carrier female
XhXh - Hemophiliac female
XHY - Normal male
XhY - Hemophiliac male
Cross a carrier female with a
normal male? What are the
possibilities in their children?
Some genetic disorders are caused by defects to an
Ex.) Monosomy – a chromosome is missing.
Trisomy – having an extra chromosome.
Sometimes only pieces of chromosomes are affected.
Ex.) Inversion, deletion, translocation.
Chromosomal defects generally affect many proteins
because so many genes are affected on the
Many of these defects lead to miscarriages.
How are chromosomal
A set of chromosomes
46 chromosomes in a human
karyotype (23 pairs).
What can be determined
from looking at a karyotype?
1. Sex of the individual.
2. Chromosomal mutations (abberations)
a) Monosomy (missing a chromosome)
b) Trisomy (extra chromosome)
c) Deletions (section of chromosome missing)
***Depending which chromosome has the
mutation, this determines the disorder…