Genetic Disorders 2022 PDF

Genetic disorders  Chromosomes and Inheritance Since genes are carried on chromosomes, knowledge of chromosome number and structure has far- reaching implications for basic genetics, human health, and evolution. Karyotype Preparation Procedure Microscope view of specimen Ch...

Genetic disorders  Chromosomes and Inheritance Since genes are carried on chromosomes, knowledge of chromosome number and structure has far- reaching implications for basic genetics, human health, and evolution. Karyotype Preparation Procedure Microscope view of specimen Chromosomes cut out & arranged X-linked Inheritance – When Men and Woman Play by Different Rules Behind the ? ball? Colorblindness is an X-linked recessive trait.  X-linked Inheritance There are many X-linked recessive traits. Pedigree analysis is a key tool in human genetic A Pedigree of a Recessive Human Trait Note that the trait can appear in offspring of parents without the trait.  A Pedigree of a Dominant Human Trait Note that the trait appears in every generation and ½ the offspring of an affected heterozygote are expected to show the trait  Changes in Chromosome Number and Structure Changes in chromosome number and structure are important for health and evolution Down syndrome is caused by a change in chromosome number  Aneuploidy Aneuploidy occurs when one of the chromosomes is present in an abnormal number of copies Down Syndrome is Caused by Trisomy for Chromosome 21 Aneuploidy is remarkably common, causing termination of at least 25% of human conceptions. Aneuploidy is also a driving force in cancer progression (virtually all cancer cells are aneuploid). Chromosome Non-Disjunction in Meiosis Causes Aneuploidy The Frequency of Chromosome Non-Disjunction And Down Syndrome Rises Sharply with Maternal Age Sex Chromosome Aneuploid Conditions are Common Turner  Polyploidy Polyploidy occurs when all the chromosomes are present in three or more copies Polyploidy is common in plants and rare in animals.  Polyploidy is a Major Force in Plant Evolution Roughly 35% of flowering plants (the most familiar plant species) arose through polyploidization Chromosome Structural Changes There are 4 types of chromosome structural change – all of them associated with human disorders A Boy with Cri-du-Chat Syndrome – a Debilitating Disorder Caused by Chromosome Deletion Cri-du-Chat is Caused by the Loss of the Short Arm of One Copy of Chromosome 5  Translocations Lead to a Number of Human Cancers In Burkitt’s lymphoma, a chromosome translocation causes a cell cycle-promoting gene to always be active.  Searching for Chromosomal Defects - Amniocentesis and Chorionic Villus Sampling Many new techniques for learning about individual genes rather than whole chromosomes are available or under development.  Removing a cell for diagnosis from a human embryo. The diagnosis: trisomy 21 (Down syndrome). Searching for Chromosome and Gene Defects – Pre-Implantation Genetic Diagnosis (PGD ) What is Down Syndrome? Down Syndrome is the most common chromosomal abnormality. It occurs in 1:800 to 1000 live births Cause 92% to 95% of all causes of Down Syndrome are attributable to an extra chromosome 21. Children born with extra chromosome 21 are born to parents of all ages but greater risk for women 35 years and older  Intelligence This varies from severely retarded to low normal intelligence but is generally within the moderate range.  Social Development May be 2 to 3 years beyond the mental age, especially during early childhood  Sensory Problems Myopia ,Hyperopia, excessive tearing, head tilt, cataracts.  Physical Disorders Respiratory infections Leukemia is 10 to 30 times more frequent. Thyroid dysfunction. Therapy Mega doses of vitamins and minerals. Surgery. Drugs and thyroid hormones Prognosis Life expectancy for a one year old - 76% for child with Downs, 91% without Life expectancy for a 20 year old - 53% with, 82% without  Genetic Mutations Mutagens Mutations may result from Errors in DNA replication Physical or chemical agents called mutagens Mutations in germ cells (sperm or egg) are very harmful Mutations that happen in somatic cells (regular cells) can be harmful. Most mutations in somatic cells are often harmless and not passed on. Mutations Can Cause Genetic Disease Genetic Disease: is a disease that can be passed on or inherited. – They are caused by mutations. Two examples: Tay Sachs, Sickle Cell disease Why haven’t these diseases been eliminated by natural selection and survival of the fittest?  Although mutations are often harmful – They are the source of the rich diversity of genes in the living world. – They contribute to the process of evolution by natural selection.