Genetic disorders and pedigrees

Video-Down Syndrome http://www.sosq.vcu.edu/videos.aspx

Work with a partner and answer the following question: The image you see is called a karyotype and there is a chromosome missing. How do you think this happens?

Turner Syndrome, not on exam-just example Turner syndrome is a chromosomal condition that affects development in females. The most common feature of Turner syndrome is short stature, which becomes evident by about age 5. An early loss of ovarian Many affected girls do not undergo puberty unless they receive hormone therapy, and most are unable to conceive (infertile).

Example: Down syndrome (trisomy 21 ) Nondisjunction Nondisjunction is the failure of chromosome pairs or sister chromatids to separate properly during cell division. Example: Down syndrome (trisomy 21 )

Karyotype picture of a person's chromosomes. Autosome- Any chromosome except for the sex chromosomes. Humans have 44 autosomal chromosomes

Introduction: A genetic disorder is an illness caused by one or more abnormalities in the genes Especially when a condition is present from birth (congenital) Genetic disorders may or may not be inherited non-heritable genetic disorders, defects may be caused by new mutations or changes to the DNA. We can use pedigrees to study how a genetic disorder is inherited

Pedigrees Used to study human genetics A pedigree helps us determine genotypes of the family members

1st Example: Albinism Occurs frequently in nature. Disorder caused by a recessive allele, a faulty version of the melanin gene. Albinos do not have the right “recipe” to make melanin pigment. White hair, pale skin, red or pink eyes. Causes some forms of blindness.

1st Example: Albinism Generally the result of the biological inheritance of genetically recessive alleles (genes) passed from both parents of an individual

2nd Example: Sickle Cell Anemia Red blood cells take the shape of a sickle and stick to small capillaries. Caused by a recessive allele which results in abnormal hemoglobin.

The sickle-cell allele makes people who carry it resistant to malaria a serious illness carried by mosquitos. The disease has a recessive pattern of inheritance:

2nd Example: Sickle Cell Anemia This genetic condition is a recessive trait. “Co dominant” When an individual has only one allele for the sickle cell trait, the person is a carrier. What is the genotype of individual Z? What are the parent genotypes of individual Z?

3rd Example: Huntington’s Disease Huntington disease (HD) is a disorder affecting nerve cells in the brain. Mild symptoms, which include forgetfulness, clumsiness and personality changes first appear in middle age (~40/50). Over the next 10-20 years, a person with HD gradually loses all control of their mental and physical abilities. There is no cure.

3rd Example: Huntington’s Disease The gene for HD is dominant. “Dominant Heredity” Each child of an affected parent has a chance of getting the mutant gene, and therefore has a chance of inheriting the disease.

4th Example: Cystic Fibrosis A genetic disorder which causes excess mucus to build up inside respiratory passages and digestive passages. People who suffer from this disease have shorter life span (~30-40) years and might have reproductive problems.

4th Example: Cystic Fibrosis Recessive Heredity, caused by recessive allele. No known cure, yet.

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