1. 27:3 Genetic Disorders
• Objectives:
• Describe genetic disorders in humans
• Give examples of how genetic counseling
can help families

2. Errors in Chromosome Number
• Some people can be born with more or
fewer than 23 chromosomes
• This is caused by the chromosomes not
pulling apart during mitosis phase of
meiosis
• It can happen to any chromosome but when
it happens on the sex chromosomes certain
traits show up.

3. • If a male is conceived and has only a Y
chromosomes, that child will die before it is
born
• If a XXY male or an XO female is
conceived they will live but are unable to
make new sex chromosomes
• If a child is born with an extra chromosome
then the child is said to have Downs
Syndrome, which means they will learn at a
slower rate, have heart problems and have
different physical traits.

4. Genetic Disorders and
Autosomes
• Some genetic disorders can be found on
autosomes. These are the genes that are not
sex genes
• These result if a chromosome does not pull
apart during meiosos
• Dyslexia, which is a reading and writing
disability, is caused by a dominant gene

5. • PKU is a genetic disorder where the body
does not break down some chemicals
properly
• This can cause brain damage
• Today all babies are tested for PKU at birth
and if it is found then a special diet is
started with very few of these chemicals
and the baby can develop normally
• Hemophilia, Cystic Fibrosis are other
genetic disorders

6. Genetic Counseling
• Genetic counseling is the use of genetics to predict
and explain the traits in children
• A genetic counselor can tell if a problem is cause
by genes
• The counselor looks at the parents pedigree and
determine if they are at risk of having a child with
a genetic disorder
• A pedigree is a diagram which shows how a
certain trait is passed along in a family