1. Human Genetic Disorders
A genetic disorder is an abnormal condition that a person inherits through genes or chromosomes.
Genetic disorders are caused by mutations, or changes in a person’s DNA.

2. Human Genes and Mutations
Mutations happen when an error occurs while copying the DNA sequence
Not all mutations are harmful, some are beneficial and others have no effect at all
Certain chemicals, x-rays and radioactive substances can cause mutations

3. Chromosome Disorders
Individual, or point, mutations can occur, but an error can occur with the number of chromosomes that should be inherited
These mistakes usually occur in meiosis
Chromosome number is too many or too few
Results from Non-disjucntion
An incorrect number of chomosomes is often fatal to an unborn embryo or fetus, or the baby dies shortly after birth
Down Syndrome-3 copies of Chromosome #21

4. Common Genetic Disorders
Cystic Fibrosis
Body produces abnormally thick mucus in the lungs and intestines that can lead to bacterial infections
Causes difficulty breathing and digesting
It is a recessive allele (both parents must carry it) and has no known cure
Sickle-cell disease (Sickle-cell Anemia)
Caused by abnormal hemoglobin (protein that carries oxygen) causing pain and weakness
The allele for it is co-dominant.
People with two sickle cell alleles have it
People with one sickle-cell allele produce
both normal and abnormal hemoglobin but
don’t usually have symptoms. There are
treatments but no cure.

5. Common Genetic Disorders cont.
Hemophilia
Disorder that causes the blood to clot slowly or not at all. One of the proteins needed for normal clotting is not produced.
It is caused by a recessive allele on the X chromosome and thus is sex-linked.
Occurs more often in males than females.
Can develop after birth but usually genetic.
Down Syndrome
Due to an extra copy of chromosome 21
Occurs when chromosomes fail to separate during meiosis
Down Syndrome patients have a distinct appearance and some degree of mental retardation but many lead full active lives

6. Modern Approach to Genetic Disorders
Doctors can detect genetic disorders using amniocentesis and karyotypes
Amniocentesis: chromosomes from fluid surrounding the baby are examined
Karyotype: a picture of the chromosomes revealing whether the baby has the right number or whether it is a boy or girl
Couples with family histories of disorders must weigh the chances of children having a disorder. Karyotypes, pedigrees and Punnett squares can help with determining the potential risks