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“You will never change your life until you change something that you do daily” - John C. Maxwell “There is nothing in the caterpillar that tells you it I going to be a butterfly” - Buckminster Fuller Units of Heredity Chapter 12 Understanding Genetic Disorders Down Syndrome is caused by an extra chromosome, but how does one pass on an extra chromosome? Why are color-blindness and baldness typically found only in men? Are diseases dominant or recessive like other traits? Do sex chromosomes only code for the sex of the offspring or are their traits associated with each sex chromosome? Discovery of Sex-Linked Traits Thomas Morgan at Columbia University, 1908 Fruit fly (Drosophila melanogaster) Discovered link between specific trait and ____________ Model organism X-linked trait Discovered crossing over Genetic recombination Reciprocal Cross Reciprocal cross: experiment to test the role of _____ on the inheritance of a trait X-Linked Inheritance X-linked disorders: genetic disorders caused by genes found on the X chromosome Ex: color blindness __________ disorder: genetic disorder that does not exist in the presence of a functioning allele Presence of a defective gene on one allele will result in the expression of the functional allele on the other chromosome ____________ recessive disorder: found on non sex chromosomes X-linked recessive disorders: found on X chromosome Spermatogenesis and the Sex of the Child Half of the sperm produced have X chromosome and half have Y chromosome 50% chance of having either a boy or a girl X-linked Recessive Disorders: Color Blindness Genes that code for red and green absorbing pigments are found close together on the X chromosome Females have a back-up X chromosome, males do not Check your Understanding X-linked recessive disorder Father’s genotype Hemophilia In this situation the mother does not suffer from hemophilia, but her father had hemophilia. The father does not suffer from hemophilia. Predict the chances of having a son with hemophilia. Mother’s genotype Ex. X X X Y Check you Understanding X-linked dominant disorder Father’s genotype Rett syndrome In this situation the mother’s father had Rett syndrome, while her mother did not. The father does not suffer from Rett syndrome. Predict the chances of having a daughter with Rett syndrome. Mother’s genotype Ex. X X X Y Linked vs. Sex Linked Linked traits: genes that are located on the ___________________ Sex linked or x-linked traits: genes that are located on the X-chromosome Linked Traits Almost always ________ ________ during meiosis Linked traits violate the principle of independent assortment Crossing Over and Linked Traits _______________ chromosomes: chromosomes with a combination of alleles that are different from that of the parent chromosomes Due to _____________ Linked Traits Genes that are located near each other on the chromosome have a tendency to be inherited together Ex. Red hair and freckles Autosomal Genetic Disorders Genetic disorders associated with non-sex chromosomes or autosomes Autosomal recessive disorder: a genetic disorder that occurs when ______ chromosomes in the pair contain a defective gene Ex. Sickle cell anemia, Albinism Autosomal dominant disorder: a genetic disorder that occurs when the offspring receives one defective allele from parent Typically one of the parents has the disease Genetic Disorders Type Name of Condition Effects X-linked recessive disorders Hemophilia Duchenne muscular dystrophy Red-green colorblindness Faulty blood clotting Wasting of muscles Inability to distinguish shades of red from green Autosomal recessive disorders Albinism Sickle-cell anemia Cystic fibrosis Phenylketonuria Tay-Sachs disease Werner syndrome No pigmentation in skin Anemia, intense pain, infection Impaired lung function, lung infections Mental retardation Nervous system degradation in infants Premature aging Autosomal dominant disorders Huntington disease Marfan syndrome Polydactyly Brain tissue degradation Ruptured blood vessels Extra fingers and toes Aberrations in chromosome number Down syndrome Turner syndrome Klinefelter syndrome Mental retardation, shortened life span Sterility, short stature Dysfunctional testicles, feminized features Aberrations in chromosome structure Cri-du-chat syndrome Fragile-X syndrome Mental retardation, malformed larynx Mental retardation, facial deformities Autosomal Recessive Disorder __________: a person who does not suffer rom the recessive genetic disorder but who carries an allele for it that can be passed along to their offspring Ex. Person heterozygous for albinism Autosomal Recessive Disorder Sickle-cell anemia: defective hemoglobin protein causes Both mother and father must have at least one allele for sickle cell anemia 25% chance that offspring will get the disease Sickle-cell anemia Autosomal Dominant Disorder Ex: Huntington's disease is Tracking Traits ___________: family history used to track genetic conditions Sample Problem A = Cystic fibrosis (cc) = Unaffected (CC or Cc) CC E B Cc F C G D = Polydactyly (PP or Pp) = Unaffected (pp) Sample Problem ? F A ? B C D E Polyploidy Polyploidy: a condition in which one or more ____________ of chromosomes have been added to the genome of a diploid organism Aneuploidy Aneuploidy: a condition in which an organism has ______________ chromosomes than normally exist in the species full set Possibly responsible for 30% of miscarriages 30% of pregnancies end in miscarriage Down Syndrome is the result of aneuploidy Down Syndrome Nondisjunction Nondisjunction: failure in the ___________ of homologous chromosomes (Meiosis 1) or sister chromatids (Meiosis II) during cell division Genetic Disorders in Sex Chromosomes Genetic disorders associated with sex chromosomes are not inherited but are the result of _______________ Turner Syndrome Female with single X chromosome Klinefelter Syndrome Male with extra X chromosome XYY Male Male with extra Y chromosome XXX Female Female with extra X chromosome Turner Syndrome Only one healthy X-chromosome Other chromosome is missing or altered Occurs in 1 of 2,500 human females Characteristics ____________ between neck and shoulders Short stature Often sterile, underdeveloped ovaries Klinefelter’s Syndrome Extra x-chromosome in human males Occurs in 1 of 1,000 human males Characteristics Underdeveloped testes Development of some female features ___________ and taller than average Lower testosterone, infertile Aneuploidy and Cancer Additional or fewer chromosomes in _________ cells Occurs during mitosis Not every cell in the body is affected, as in aneuploidy on sex cells Almost all _________ are aneuploidy Not sure if a cause of effect of cancer cells Structural Aberrations in Chromosomes ______________: deviation from the normal Can occur spontaneously, or as a result of exposure to radiation, viruses, or chemicals Structural Aberrations in Chromosomes Deletion: chromosome fragment breaks off and fails to reconnect with the chromosome Ex: Cri-du-chat syndrome = deletion of section from chromosome 5 ___________: chromosome fragment rejoins chromosome in an inverted fashion Translocation: exchange of pieces from two ___________________ chromosomes Duplication: section of DNA is duplicated during crossing over Can have negative effect, but can also be beneficial Cri-du-chat Syndrome Cri-du-chat Syndrome: results from a deletion of chromosome 5 Characteristics Mental retardation Improperly developed ______ Small head Low-set ears Missing section of chromosome 5 Pre-implantation Genetic Diagnostics (PGD) Screening of genotype of potential embryos prior to in-vitro fertilization (IFV) 1. 2. 3. 4. Hormones stimulate egg maturation Egg collection Fertilization Removal of embryonic cell during 8-cell stage Couples with family history of genetic disorders Parents can choose _____ of child Methods of Fetal Testing ___________________: cells obtained from amniotic fluid of 14-18 week old fetus Chorionic villus sampling (CVS): sample taken from placenta tissue at 8-10 weeks of development