Genetics and Genetic Diseases

Genetics  Study of inheritance and human disease  1860’s – Gregor Mendel  Gene = DNA  RNA  Proteins (enzymes)  permit specific biochemical reactions to occur  Genes determine the structure and function of the human body

Chromosome  Chromosomes are made of chromatin (DNA)

Human Genome Project  Genome – entire collection of genetic material in a cell  2001 – rough draft published 30,000 genes 1% carries genes, rest is filler  Genomics – analysis of genome  Proteomics – proteins encoded by genes, goal is to understand role of each protein

Ideogram  Simple cartoon of chromosome P-arm – shorter segment Q – arm – longer segment Bands – show landmarks

Chromosomes  46 chromosomes in a cell, 23 pair  22 pair – autosomes (body cells)  23 rd pair – sex chromosomes XX, XY Undergo meiosis, produce sex cells (gametes) Sperm meets egg = zygote

Genetic Variation  Independent assortment  Crossing over  Random fertilization

Gene Expression – Mendel Complete Dominance  Dominant – CC, trait seen  Recessive – cc, trait only seen if both alleles are recessive  CC – homozygous dominant  Cc – heterozygous  cc – homozygous recessive  Example: Albinism

Gene expression  Codominance – both alleles are dominant Ex – blood type A, B, O, AB  Incomplete dominance – hybrid Pink flowers  Sex linked – non-sexual trait carried on X or Y chromosome, sometimes called x- linked since X chromosome is largest Hemophilia, color blindness

Genetic Mutations  Change in DNA, genetic code Can occur spontaneously Mutagens – cause mutations Carcinogens – cause cancer, viruses Damage to chromosome, deletion  can be beneficial

Mitochondrial DNA  Powerhouse of cell with own circle of DNA  Inheritance occurs only through the mother sperm mitochondria do not survive during fertilization Codes for only a few important enzymes carry mutations that produce disease  Leber’s hereditary optic neuropathy  Parkinsons  Alzheimers

Mechanisms of Genetic Disease  Single gene diseases  Genetic predisposition – not solely caused by inheritance, but environmental  Non-disjunction – failure of chromosomes to separate Trisomy – triplet of chromosomes (Down syndrome) Monosomy – single chromosome only (Turner syndrome)

Single gene diseases  Cystic fibrosis Recessive Chromosome 7 CFTR gene regulates transfer of sodium ions across cell membrane and serves as chloride ion channel

Phenylketonuria - PKU  Recessive  Fail to produce enzyme phenylalanine hydroxylase Converts aa phenylalanine into tyrosine Lack of enzyme results in accumulation and presence of phenylketone in urine which destroys brain tissue. Identified at birth Diet restrictions

Chromosomal diseases  Down syndrome, Trisomy 21  Not inherited, result of nondisjunction  Characterized by Varying range of mental retardation Distinctive facial appearance Enlarged tongue…

Klinefelter syndrome  Nondisjunction of sec chromosomes – XXY  Characteristics Long legs Enlarged breasts Low intelligence…

Turner Syndrome  XO, monosomy female  Characteristics include: failure of sex organs maturing dwarfism or short stature cardiovascular defects…  Can be treated with hormone therapy, surgery

Prevention and treatment of genetic diseases  Genetic counseling – professional consultation Help to determine risk Help evaluate whether offspring have a genetic disorder Offer advice on treatment, care  Tools Pedigree Punnett square karyotype

Pedigree  Shows relationships in a family over several generations

Punnett square  Box used to determine the probability of inheriting genetic traits Monohybrid dihybrid

Karyotype  Used to find chromosomal disorders  Use a sample of cells (cheek, wbc)  Cells in metaphase are stained and photographed  Chromosomes cut and arranged according to size

Amniocentesis  Fetal cells floating in amniotic fluid are collected using a LARGE syringe

Chorionic Villus Sampling  Cell from chorionic villi are collected from area surrounding embryo  Cells are grown in petri dishes, then analyzed

Treating Genetic Diseases  No cure, but some can treat symptoms  Gene therapy Gene replacement – replace abnormal with normal Gene augmentation – normal cells are introduced and add normal proteins