Genetics Genetically Linked Diseases Chapter 22 Pages 469

Genetics & Genetically Linked Diseases Chapter 22 Pages 469 – 474

Page 469 v In Genetics sexual reproduction, a new individual is created from the union of the sperm cell & the egg. • This means that half the genetic material comes from mom & half comes from dad v Genetics = the branch of biology that studies how the genes are transmitted from parents to their offspring. v Mutation = the appearance of a new & different traits caused by the inheritance of a mutated (or changed) gene or chromosome. v Human genome = complete set of nucleic acid sequence for humans (both coding & noncoding DNA)

Page 469 Types of Mutations v Gene Mutations occur occasionally at random in all cells v Somatic cell mutation = genetic alteration acquired by a cell that can be passed to the progeny of the mutated cell in the course of cell division. v Chromosomal mutation = change in the number of chromosomes found in the nucleus or a change in the structure of a whole chromosome.

Page 469 Lethal Genes Inherited mutations generally have negative consequences for individuals v An inherited gene that results in death is a lethal gene v The time at which lethal genes exert their deadly influence varies v Each person may carry 2– 3 different recessive lethal genes v Two similar recessive genes must be present in an individual for the gene to be expressed v People with common ancestry are more likely to share many genes v

Pages 469 – 471 Human Genetic Disorders Difference between genetic & congenital disorders v Phenylketonuria = a human metabolic disorder caused by an enzyme deficiency v Sickle cell anemia = a blood disorder common in individual of African descent. v Tay-Sachs disease (genetic disorder) = caused by a mutation resulting in a deficiency of a lysosomal enzyme. v Duchenne’s muscular dystrophy = muscles suffer a loss of protein & the contractile fibers are eventually replaced by fat & connective tissue, rendering skeletal muscle useless. v

Page 471 Human Genetic Disorders (Cont’d) Huntington’s disease = characterized by the degeneration of the CNS, which ultimately results in abnormal movements & mental deterioration. v Cystic fibrosis = a disease of the exocrine gland. v Thalassemia = disease found among those of Mediterranean descent (symptoms same as those of anemia) v Hemophilia = a sex-linked genetic disorder, which means it is only transmitted on the X chromosome. v Chromosomal aberrations (examples – Turner’s syndrome, Klinefelter’s syndrome, Down syndrome) v

Page 472 Mutagenic Agents v Mutagenic agents = agents that increase the occurrence of mutations v Examples: cosmic rays, ultraviolet rays from the sun, X-rays, radiation from radioactive elements, benzene, formaldehyde, phenol, & nitrous acid

Page 472 Genetic Counseling Involves talking with parents or prospective parents about the possibility of genetic disorders v Individuals who may benefit from counseling • Those who think they have a birth defect or who have a family member with a genetic disorder • Women who are pregnant after the age of 34 • Couples who have had one child born with a genetic defect • Women who have had two or more miscarriages or whose babies died in infancy v

Page 472 Genetic Counseling (Cont’d) Couples who need information about genetic disorders that occur frequently in their ethic group • Couples who are first cousins or other blood relatives v After careful analysis a genotype is determined v Diagnostic tests •

Pages 472 – 473 Advances in Genetics v Genetic engineering – Manipulation of genes • The aim is to introduce new characteristics or attributes v Gene therapy – Correcting defective genes