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Lecture 5

Lecture 5 - Mendelian Diseases

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Esteban Parra

Mendelian Diseases Mendelian Inheritance and Human Diseases - Thousands of simple Mendelian diseases (caused by mutations in one gene) have been described in humans. - Individually, these diseases are not frequent, normally affecting less than 1/1,000 births. However, their global impact is huge. - The role of genetic counselors is to give advice to individuals suffering from these diseases and to their families. - Transmission of diseases in families is usually depicted using pedigrees. - Carrier only makes sense when you are referring to a recessive allele Mendelian Diseases: Dominant Trait - Dominant traits are which a heterozygous (with both defective and normal allele), the individual will show the disease - If this person with a disease mates with a normal female, he can still pass the defective allele 50% of the time - 50% will be homozygote for the normal allele Autosomal Dominant Inheritance - Usually one affected parent o By definition these diseases are rare and infrequent - Homozygotes are rare - Affects either sex o Because this is autosomal, you can pass to either female or to male offspring - Transmitted by either sex Some Major Autosomal Dominant Disorders - Familial hypercholesterolemia - Familial breast cancer o The most common form is unable to follow through families o Familial breast cancer is where you can see in pedigree where it is passed on from generation to generation o BRCA1 and BRCA2  having this gene, you will have a higher risk of breast cancer - Familial Alzheimer’s disease - Neurofibromatosis type 1 - Huntington’s disease Mendelian Diseases: Recessive Trait - Recessive disease – if you are heterozygote, you will be a carrier and phenotypically normal - The individual will be a carrier, and able of passing on the affected allele to offspring Autosomal Recessive Inheritance - Parents usually unaffected - Parents usually carriers. Carriers may be common - There is a 25% chance that the offspring of two carriers will be affected - More frequent in consanguineous matings and genetic isolates. - Affects either sex - Affected are always homozygous Some Major Autosomal Recessive Disorders - Cystic fibrosis - Phenylketonuria - Tay-Sachs disease - Sickle
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