2PRE LECTURE QUIZ (TRUE/FALSE) Most genetic disorders are caused by an alteration in the deoxyribonucleic acid (DNA) sequence that alters the synthesis of a single gene product.Autosomal recessive disorders are manifested even if only one member of the gene pair is affected.A teratogenic agent is an environmental agent that produces abnormalities only during the first 4 weeks of embryonic or fetal development.Down syndrome, Turner syndrome, and Klinefelter syndrome are all examples of chromosomal disorders that occur from an alteration in chromosome number.Cleft lip and palate is an example of an autosomal dominant disorder.TF
3PRE LECTURE QUIZAutosomal dominant disorders involve a ______________ mutant allele that is transmitted from an affected parent to an offspring.Sex-linked disorders almost always are associated with the __________ chromosome and are predominantly recessive.An individual with ______________ syndrome would be female, short in stature, and lacking in breast development, and would not menstruate._____________________, an autosomal dominant disorder, is a condition involving neurogenic tumors that arise from Schwann cells and other elements of the peripheral nervous system.Neural tube defects are often the result of ______________ acid deficiency.NeurofibromatosisSingleFolicTurnerX
4Genes Are Found on Chromosomes X or Y chromosome: sex-linkedOther chromosomes: autosomal
8Alleles Alleles are copies of a gene If all your copies of a gene are alike, you are homozygousIf they differ, you’re heterozygousIf you are heterozygous for a recessive trait and do not show it, you are a carrierIf you have only one copy of a gene, you are hemizygous
9QuestionWhich of the following statements is true about an individual who is a carrier for the cystic fibrosis (CF) gene?Homozygous; suffers from CFHomozygous; does not suffer from CFHeterozygous; suffers from CFHeterozygous; does not suffer from CF
10AnswerHeterozygous; does not suffer from CFIf an individual is a carrier, they are heterozygous for the recessive trait (in this case, CF), but they do not display the trait (because the trait is recessive).
11Sometimes: It has intermediate penetrance Discussion:If you have the allele for a trait, do you display the trait?No: It is recessiveYes: It is dominantSometimes: It has intermediate penetrance
12Scenario: A Young Man’s Father Died of Brugada Syndrome … Unexplained sudden deathDue to mutation in the gene from the Na+ channel in cardiac muscleAutosomal dominant traitHis mother is alive and healthyBoth grandmothers are alive and healthyQuestion:What is the son’s chance of having the disease?
14PenetranceBrugada syndrome has only a 12.5% penetranceWhat does this mean for the young man whose father died of it?
15Sex-Linked Traits The gene is usually on the X chromosome If Brugada syndrome were sex-linked, what would the young man’s father’s genotype have been?What would his chances of inheriting the disease be?
16QuestionIf an unaffected mother carries one normal and one mutant allele on her X chromosome, what are the chances that she will transmit the defective gene to her sons?25%50%75%100%
17Answer50%Because a son receives the X sex chromosome from his mother (who has one normal and one mutant allele), there is a 50% chance that the mutant allele will be inherited.
19Mitochondrial DNA Codes for the proteins needed for aerobic metabolism Mitochondria all come from the motherShe has many more than two mitochondria,so she may pass several different mitochondrial alleles to the child(Mendelian Inheritance in Man. . Mitochondrial deafness modifier gene. Retrieved May 15, 2005, from dispomim.cgi?cmd=entry&id= )
20Chromosomal Damage Breakage and rearrangement Deletion Inversion Isochromosome formationRing formationTranslocation
21QuestionWhich type of chromosome alteration generally results in normal offspring?DeletionInversionTranslocationRing formation
22AnswerTranslocationTranslocation is the only chromosomal alteration where no genetic material is actually lost (chromosome parts are exchanged), so the offspring are usually normal. Offspring are translocation carriers, so their children may or may not be normal.
23Alterations in Chromosome Duplication MosaicismAneuploidyMonosomyPolysomyTrisomyDown syndrome
26Environmental Causes for Congenital Disorders Scenario:Mrs. K is a diabetic and is having trouble keeping her blood glucose constant during pregnancy…She works in a dry-cleaners store next to a gas station and drinks heavily.She is diagnosed with toxoplasmosis.Question:What kinds of stresses is her fetus experiencing?