Transcript Chapter 15
Chapter 15: Human Genetics • Karyotypes, Down Syndrome, sex chromosomes, abnormalities, autosomal genes, sex-linked genes, and polygenic inheritance are covered in this Chapter. Inheritance 0f Chromosomes • Somatic cells - 22 pairs of autosomes, 1 pair sex chromo • Karyotype - shows chromo’s paired by size, shape, & appearance in metaphase • members in a pair have same banding patterns Inheritance 0f Chromosomes • Nondisjunction occurs during meiosis, causing abnormal chromo # • Nondisjunction is the failure of one or more chromo’s to separate during MI or when daughter chromo’s fail to separate during MII. Inheritance 0f Chromosomes • Down Syndrome common autosomal trisomy • 3 copies of chromo 21 • 23% cases sperm had extra chromo 21 • chance of woman having down syndrome child increases w/ age. Abnormal Sex Chromosomal Inheritance • Turner (XO) syndrome - females have only one X chromo • Females are short, broad chest, folds of skin on neck • Ovaries never functional, never undergo puberty Abnormal Sex Chromosomal Inheritance • Klinefelter syndrome males have one Y and 2 X chromos • individuals have large hands and feet and long arms and legs. Abnnormal Sex Chromosomal Inheritance • Triplo-X females • Jacob syndrome (XYY) • Males w/Jacob’s syndrome are taller than average, have persistent acne, tend to have lower intelligence Abnormal Sex Chromosomal Inheritance • Fragile X Syndrome X chromo nearly broken, most often found in males • hyperactive or autistic children, delayed speech • Traced to excessive copies of CGG triplet Autosomal Genetic Disorders • Males=squares, females=circles • Carrier- Has no apparent abnormality but can pass on allele for recessively inherited genetic disorder Autosomal Dominant Disorders • Neurofibromatosis have tan skin spots at birth that turn to benign tumors • 1 in 3,000 people effected • Neurofibromas are lumps under the skin of nerves and other cells Autosomal Dominant Disorders • Huntington Disease effects 1 in 20,000 • leads to degeneration of brain cells • Death in 10-15 years from onset • Gene for disease on chromo 4; contains repeats of CAG Autosomal Recessive Disorders • Cystic Fibrosis - most common lethal genetic disease in Caucasions • 1 in 20 is a carrier, 1 in 2,500 has disorder • Production of mucus in lungs and pancreas • Gene on Chromo 7 Autosomal Recessive Disorders • Tay-Sachs Disease - in Jewish people • Symptoms not apparent, child becomes blind & helpless, develops seizures. • Death by 3-y yrs. • Lack of enzyme hexosaminidase Autosomal Recessive Disorders • Phenylketonuria(PKU) • 1 in 5,000 births • Lack of enzyme needed to metabolize aa phenyalanine • Mutated gene on chromo 12 • Child placed on low phenyalanine diet till age 7. Beyond Simple Mendelian Inheritance • Polygenic Inheritance - 1 trait governed by 2 or more sets of alleles • Includes diabetes, schizophrenia, allergies, and cancers • Beyond Simple Mendelian Inheritance Sickle-cell disease controlled by incomplete dominant alleles • Blood cells irregularly shaped (abnormal hemoglobin), clog vessels and break down • poor circulation, anemia, low resistnce to infection, jaundice... Sex-linked Genetic Disorders • Traits controlled on sex chromo are sexlinked • Y-chromo smaller, most sex linked are on the X-chromo • Males get X-linked traits from mom • Daughter must have a carrier mom and an expressed dad. Sex-linked Genetic Disorders • Color Blindness recessive disorder involving mutations of genes coding for green or red sensitive cone cells • Cannot see red or green respectively Sex-linked Genetic Disorders • Muscular Dystrophy characterized by wasting away of muscles, eventually leading to death • 1 in 3,600 births • fails to produce protein dystrophin • waddling gait, toe walking, frequent falls, difficulty rising. • Death by 20 yrs old Sex-linked Genetic Disorders • Hemophilia - impaired ability to clot • 1 in 10,000 males • Hemophiliacs bleed externally after an injury and also suffer internal bleeding around joints • Need blood transfusions or conc. of clotting protein