Mutations Chapter 9

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

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

Substitution Substitutions result when the wrong nucleotide base moves in to the space May or may not result in a genetic disorder

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.

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.

Nondisjunction in Sex Chromosomes XXX or XXY yields Klinefelter syndrome XO yields Turner Syndrome Y Chromosome XYY – Antisocial ?

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

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.

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

Copyright © McGraw-Hill Companies Permission required for reproduction or display