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.

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

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

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.

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. http://www.sciencecases.org/hemo/hemo.asp 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

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