BIOLOGY 111 1st Edition Lecture 17 Outline of Last Lecture I Mendelian Genetics II Segregation of Alleles III Phenotype and Genotype IV Law of independent assortment V Probability Formulas Outline of Current Lecture I Epistasis II Pedigree Analysis III Inherited Disorders in Humans IV Chromosome Theory of Inheritance Current Lecture Epistasis a form of gene interaction where one gene effects the expression of the other masks the phenotypic expression of another o epistatic allele o hypostatic allele opposite of epistatic o ex B controls color E controls expression of B if a dog gets one dominant E allele EE or Ee the color expressed will depend on b allele BB or Bb black bb brown if a dog gets a homozygous recessive e allele ee the dog will be golden regardless of the b allele ee is epistatic to b allele b allele is hypostatic to e allele Pedigree Analysis if given genotypes we should be able to recognize type of trait o dominant AA or Aa traits are observed in each generation and are more common o recessive aa traits tend to skip generations and are less common Inherited Disorders in Humans o usually due to recessive inheritance must inherit both homozygous recessive alleles o Cystic Fibrosis o common lethal genetic disease one in 2500 These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute o recessive trait CFTR gene aa cystic fibrosis abnormal CFTR gene A AA or Aa normal normal CFTR gene homozygous aa pass on gene and have the gene homozygous AA do not pass on nor do they have the gene heterozygous Aa are carriers they carry the gene but do not show any of its affects and appear normal o modifier genes TGFB1 on chromosome 19 contribute to the severity of cystic fibrosis influences immune response to infection leading to more infection more scarring of lung tissue inherited as a recessive allele Sickle cell anemia disease o common affecting one out of 400 african americans o caused by a substitution of a single aa in the hemoglobin o aa have the disease Aa carriers AA do not have the disease o Pros are resistant to malarial disease o Cons experience physical weakness pain organ damage and sometimes paralysis o pleiotropic one gene affects more than one phenotype character ex phenylketonuria reduced hair pigmentation mental retardation Achondroplasia dwarfism o rare dominant allele lethal homozygous dominant alleles heterozygous dominant allele causes dwarfism two dwarf parents must each be heterozygous have 5 chance having a normal child 5 chance dwarf homozygous recessive alleles are normal Huntingtons disease o dominant allele disorder o it is a degenerative disease of nervous system Chromosome Theory of Inheritance transmission of chromosomes genes reside on chromosome within the nucleus Sex determination System o Humans X Y o Insects X O o Z Y o Haploid Diploid system Drosophila melanogaster o XX XY sex system Y not male determining factor o ratio between X chromosomes determines the number of sets of autosomes X A X A 5 male X A 1 female Wild Types are normal in regards to mutation Y Chromosome y liked genes mostly sex determining factors X Chromosome x linked genes o a phenotype determined by an allele on the x chromosome o recessive x linked genes a normal copy on one X masks the recessive disease allele on the other X female heterozygous carrier shows no effect o a male has a single X chromosome so he will show the effects of any recessive alleles located on the X chromosome males have only one X chromosomes they are hemizygous for x linked gene o dosage compensation maintains chromosome balance inactivating one Xchromosome at random in each cell inactivates by XIST gene Sex linked genes if genes found on one of the two chromosomes but not on both