HLTH 335 1st Edition Lecture 6 Chapter 5 Heredity Cancer Objectives Describe DNA s composition and its role in heredity Describe general mechanisms of transmission of hereditary diseases and give examples Explain genetic diseases based on abnormal chromosome construction Discuss screening techniques and the concept of gene therapy Distinguish between congenital and hereditary conditions Heredity The Basics DNA the blueprint for directing cell activities Chromosomes assembled strands of DNA within the nucleus 44 autosomes 22 pairs 2 sex chromosomes Female XX Male XY Karyotype the complete chromosomal composition Chromosomes can be extracted from the nucleus photographed under a microscope in order to detect abnormalities Genetic Inheritance Genes for a particular trait e g hair color occupy a particular site on a chromosome Each person has 2 copies of each gene 1 from each parent Alleles alternate forms of a gene Homozygous the same e g BB or bb Heterozygous different e g Bb Dominant when only one allele is need to express a trait e g Bb results in brown hair Recessive when two are needed to express a trait e g the red hair allele is recessive Autosomal Dominant Diseases Occur through transmission of a dominant allele Offspring have 50 chance of being affected if one parent has normal karyotype Males and females have equal chance of being affected Examples of Autosomal Dominant Diseases Polydactyly having extra fingers or toes Achondroplasia autosomal dominant Abnormal cartilage formation Marfan syndrome autosomal dominant The connective tissue protein fibrillin is missing These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute people are tall and thin believe Lincoln had it Familial hypercholesterolemia Autosomal Recessive Diseases Disease manifests when individual is homozygous for the defective allele Heterozygous parents are carriers they do not have the disease Child has a 25 chance of being affected Recessive allele appears more frequently in close intermarriages Examples of Autosomal Recessive Diseases Sickle cell anemia The black population most at risk 1 in 12 are carriers Hemoglobin is abnormal results in deformed red blood cells Deformed cells lodge and block circulation SUPER INTERESTING FACT Heterozygous individual does not have the disease but will experience mild anemia BUT The defective allele confers increased resistance to malaria which kills 2 million people a year Watch this http www youtube com watch v 2CsgXHdWqVs More Examples Galactosemia Tay Sachs disease Albinism Be able to tell everything you know about one of these Ex incidence rate who is most affected etc Sex Linked Inheritance Defective gene on X chromosome Y chromosome is small and carries few genes Defective X on male is unmasked so the trait is expressed less common for women to develop X related diseases Far less common for females to inherit x linked diseases Heterozygous female is carrier for the disease Male transmits the defective allele to his daughters Examples of Sex Linked Diseases Color blindness inability to distinguish colors specifically between red and green Rare in women Occurs in 1 out of 10 men Hemophilia Inactivation of an intrinsic clotting factor causes bleeding for longer period of time than normal NOT faster or more profuse bleeding just bleeding for longer periods of time Abnormal Chromosome Diseases as opposed to diseases caused by defective genes like we ve discussed so far Potential problems Altered number or structure of chromosomes Failure of chromosome to separate during cell division Complete loss of autosome usually incompatible with life leads to spontaneous abortion Down Syndrome Trisomy of small chromosome 21 have 3 rather than 2 Many fetuses are aborted early in pregnancy 70 75 spontaneously miscarriages Incidence 1 out of 800 Higher with advancing maternal age 1 in 50 if mother is 40 years old Characteristic appearance mild to moderate mental retardation Down Syndrome Common Complications Heart defects half of all with DS Leukemia more likely to develop in young children with DS Infectious Diseases more susceptible due to abnormalities in immune system Dementia often begins before age 40 Sleep Apnea soft tissue skeletal abnormalities lead to obstruction of airways Obesity Other gastrointestinal blockage thyroid problems early menopause seizures hearing loss premature aging skeletal problems poor vision Down Syndrome Life Expectancy 70 75 of DS babies will die in utero Of live births 15 die before one year of age 35 die before 50 years of age 50 live beyond 50 years of age FACT In 1929 50 only lived to age 10 More Examples of Abnormal Chromosome Diseases Cri Du Chat Syndrome Turner Syndrome Klinefelter Syndrome Hermaphrodites Pick one of these or one out of the previous 3 to know about for the test Genetic Counseling A genetic counselor usually begins with a complete family history of both prospective parents A complete detailed family history is called a pedigree Pedigrees demonstrate the pattern of inheritance of a genetic disease within a family When the pedigree is complete the genetic counselor can inform prospective parents of the possibility of having genetically abnormal offspring and they can make an informed decision Diagnosis of Genetic Diseases Early diagnosis is critical to prevention and treatment of genetic diseases During amniocentesis a small amount of amniotic fluid is withdrawn after the 14th week of pregnancy Amniocentesis can detect approximately 200 genetic diseases Gene Therapy A procedure that involves identification manipulation and transference of genetic segments into a host to replace defective genes and to perform desired genetic activities The genetic material used is compatible with human DNA that may be cultured in a microbe and delivered in a viral package or by injection Also referred to as genetic engineering Congenital Diseases Appear at birth or shortly after but they are not caused by genetic or chromosomal abnormalities Congenital defects usually result from some failure in development during the embryonic stage or in the first 2 months of pregnancy Therefore congenital diseases cannot be transmitted to offspring 2 3 of all newborn infants have congenital defects that are recognizable at birth Additional 2 3 defects NOT recognized at birth developmental defects demonstrated later as infants grow older 25 50 spontaneously aborted