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Mutations Copyright © McGraw-Hill Companies Permission required for reproduction or display Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Mutations and Genetic Disorders • • A mutation is a mistake in the DNA code. Genetic disorders are the harmful effects caused by mistakes in the DNA code. Most disorders are rare because affected individuals often die at a relatively young age, or cannot reproduce. Most, but not all mutations, are recessive. - Huntington’s Disease is dominant Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Mistakes during Replication • Frame shift mutation-reading frame is moved up or down depending on whether a base is added or removed from the sequence Base Insertion Base Deletion Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Substitution • • Substitutions result when the wrong nucleotide base moves in to the space May or may not result in a genetic disorder Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Genetic Recombination • • • Crossing Over If 2 genes are located far apart on a chromosome, crossing over is more likely to occur than if they are close together. Frequency of crossings can be used to construct a genetic map. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Abnormalities Due to Chromosome Number • Failure of chromosomes to separate correctly during meiosis I or II is called primary nondisjunction. Down Syndrome caused by trisomy 21. - 1 in 1700 for mothers < 20. - 1 in 1400 for mothers >20<30. - 1 in 750 for mothers >30<35. - 1 in 16 for mothers >45. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Nondisjunction in Sex Chromosomes • • X Chromosome XXX or XXY yields Klinefelter syndrome XO yields Turner Syndrome Y Chromosome XYY – Antisocial ? Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Gene Disorders Due to Protein Alteration • Sickle-Cell Anemia is a recessive inherited disorder in which afflicted individuals have defective hemoglobin, and thus are unable to properly transport oxygen to tissues. Homozygotes have Sickle-Cell. Heterozygotes usually appear normal, but are resistant to malaria. Copyright © McGraw-Hill Companies Permission required for reproduction or display Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Curable Defects • Cystic Fibrosis Body cells of affected individuals secrete thick mucus that clogs airways of lung and affects digestion. - Defect in cf gene. Researchers currently working on methods of transmitting a working copy of cf gene via viruses. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Pedigrees • Mutations are accidental changes in genes. Rare, random, and usually result in recessive alleles. - Pedigrees used to study heredity. Hemophilia - Inherited condition where blood is slow to clot or does not clot at all. Only expressed when individual has no copies of the normal allele. Royal Hemophilia - Sex-linked Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Genetic Counseling • • Genetic counseling identifies parents at risk of producing children with genetic defects and assesses the state of early embryos. High-Risk Pregnancies Couples with recessive alleles. Mothers older than 35 years. - Amniocentesis - Chorionic villi sampling Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Copyright © McGraw-Hill Companies Permission required for reproduction or display Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies