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One gene is able to express itself regardless of the presence of the other gene
- Parents of individual may have not have the trait
- Tends to skip a generation
- May see consanguinity (blood relatives
- It is possible that:
- Neither parent has the characteristic of child, but both parents are carriers of one recessive faulty gene
- Or one or both parents have two faulty genes and all offspring have disease
the genes of the individual
the physical appearance of the individual
Carrier of a Recessive Trait
- An individual who has a recessive gene but is unaffected.
- They have the genotype, but not the phenotype
- They are able to pass the trait to their offspring
Genetic disorders of interest
Autosomal = non-sex chromosome
- Autosomal Recessive Disorders:
- Tay-Sachs disease: lack of the enzyme
- Cystic fibrosis: abnormal protein in cell membrane
- Phenylketonuria (PKU): lack of an enzyme
- Sickle-Cell disease: Abnormal RBCs
- Autosomal Dominant Disorders:
- Marfans Syndrome: defect in elastic connective tissue;
- Huntington disease: too many amino acids
Recessive: Tay Sachs Disease
- Tay Sachs Disease – missing or decreased amounts of an important enzyme (Hex A) –
- Absence of Hex A allows lipids to build up in lysosomes of cells.
Tay Sachs Disease
- More common in Jewish populations
- Lipids accumulate in brain cells
- Child’s development slows around 4-8 months old
- Progressive neurological problems
- Blind, seizures, paralyzed, death
Cystic Fibrosis - Genetic disease causing lung and digestive problems
Cystic Fibrosis (CF) and Heredity
- Body produces thick, sticky mucus that clogs the lungs, leads to infection, and serious digestive disorders
- Most common, fatal genetic disease in US
- Mutations in a single gene, (CFTR) gene, causes CF
- More common in Caucasians
- Chloride ions can’t pass thru cell membrane
- Build up of thick mucus in lungs and pancreas
- Digestive and breathing problems
- Phenylketonuria (PKU) – lacks the enzyme to metabolize phenyalanine (protein levels increased in blood and urine)
- Normal development if placed on low phenylalanine diet (especially while brain is developing)
- Build up of phenylalanine affects nervous system
- Newborns routinely tested for phenylalanine level in blood
- Treatment is diet low in phenylalanine
Sickle Cell Disease and Heredity
- RBC are irregularly shaped
- Caused by a mutation in the hemoglobin-Beta gene found on chromosome 11
- Most common inherited blood disorder in the United States
- Because of irregular shape, blood cells get trapped in small blood vessels
- Disease causes great pain (“crisis”) and increased risk of infections and blockage of vessels
Test for Sickle Cell
- Blood test that checks for hemoglobin S, the defective form of hemoglobin
- Can also be detected in an unborn baby via amniocentesis
- Diagnosis is confirmed by visualizing “sickled” cells on a blood sample
Testing for Genetic Disorders:
- Testing for a protein
- •Tay-Sachs—lack the enzyme hex A.
- •PKU—a lot of phenylalanine in the blood.
- Testing the DNA
- •Use of a genetic marker to test for a genetic mutation.
- •Use of a DNA chip to test for mutated genes.
- Males and females equally affected
- Affected individuals have one affected parent
- Characteristics may be present in all generations
- Progressive degeneration of brain cells
- Mutated gene for protein (huntington)
- Often did not know had disease until middle age – already had kids and passed it to them.
- Death occurs 10-15 yrs after onset
- Now know defect is on chromosome 4 and can test for it
- --the study of our genes and the genes of other organisms.
- •The goal/purpose is to:
- –Learn about abnormal
- sequences that lead to illnesses. Develop drugs to combat these illnesses.
- –Learn about proteomics—knowledge of the structure and
- function of proteins in the cell.
- –Bioinformatics—the application of computer technologies to the study of the genome.
- Look at patterns &Multifactorial genes
Human Genome Project (HGP)
- Genes are the code for proteins that make up all of our traits (A,T,C,G)
- We have 20-25,000 genes!
- HGP was a 13 year project completed in 2003 to identify all our genes
- Positive outcomes
- –Diagnosing and predicting disease or susceptibility
- –Disease intervention (designing drugs to target specific sites in body for fewer side effects)
- –Gene therapy – using normal genes to replace or supplement defective genes
- Negative outcomes
- - Genetic discrimination – insurance or employment
- - Individual’s choice to want to know or not about a potential inherited dz.
How can we modify a person’s genome?
- Gene therapy - insertion of genetic material into human cells to treat a disorder
- –Ex vivo therapy – cells are removed from a
- patient, altered and then returned to the patient
- –In vivo therapy – a gene is directly inserted into an individual through a vector (e.g. viruses) or directly injected to replace mutated genes or to restore normal controls over gene activity
- Gene therapy has been most successful in treating cancer
Who should have genetic testing?
- If a family history of Cystic Fibrosis, genetic screening is recommended
- –Test Parents (80-90% of carriers identified), fetus or child at birth
- Early diagnosis does improve infant health and life expectancy
In Vivo Gene Therapy
- •Cystic Fibrosis – missing a gene that codes for the transmembrane carrier of Choride ion.
- •Normal gene can be sprayed into nose or delivered to lower respiratory tract (adenoviruses or other vesicles)
- •Working on improving uptake of normal gene
Genius sperm bank
- Repository for Germinal Choice, a sperm bank
- for Nobel Prize winners
- –It’s estimated that 230 children were born as a result