GEN 3022 1st Edition Lecture 8 Outline of Last Lecture I Introduction a Simple Mendelian Inheritance b Complexity of Inheritance II Wild Type Alleles a Wild type i Definition ii Two explanations for the wild type phenotype iii Example b Genetic polymorphism c Mutant alleles i Definition ii Dominant mutants 1 Gain of function 2 Dominant negative 3 Haploinsufficiency III Incomplete Penetrance a Definition b Ex Polydactyly 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 c Degree of Penetrance IV Expressivity a Definition b Factors V Environmental Effects a Definition and examples i Coat color ii PKU b Temperature sensitive mutations i Example Siamese cats VI Incomplete Dominance a Definition b Example flower color VII Overdominance a Definition b Example Sickle Cell Anemia VIII Multiple Alleles a Definition b Example blood type c Codominance IX X linked Genes a Review b Reciprocal Cross X Lethal Alleles a Definition b Essential and nonessential genes c Conditional lethal alleles d Semilethal alleles XI Gene interactions a Gene interations b Epistasis c Note XII Complementation XIII Gene Redundancy a Definition b Gene knockout c Paralogs Outline of Current Lecture I Incomplete Penetrance a Two explanations II Blood types a Example 1 III Types of dominance a Loss of function recessive allele b Dominant negative c Incomplete dominance i Example 1 loss of function allele ii Example 2 probability d Overdominance e Complementation IV Environmental Effects V Penetrance VI Chromosomes a Homologous Chromosome b Chromatids c Sister Chromatids d Bivalents e Karyotype VII X linked recessive inheritance a Example 1 b Example 2 c Example 3 Current Lecture I Incomplete Penetrance a Two explanations for incomplete penetrance of a dominant allele are i Other genes may affect the phenotype gene interaction redundancy ii The environment may affect the phenotype environmental effects II Blood Types a Example 1 a female who is IBi has offspring with a male who is IAIA Which blood type s would not be possible for their offspring III IV i Type B and type O because the each offspring has an IA allele in his her genotype which makes IBi IBIB and ii impossible Types of Dominance a Loss of function recessive allele an allele affecting flower color in snap dragons shows simple Mendelian dominant recessive pattern of inheritance If the recessive allele is a loss of function allele a reasonable explanation for the phenotype of this trait is i 50 of the functional protein gives the same phenotype as 100 this means that a heterozygote will display the dominant trait b Dominant negative i Two proteins interact to form a complex When a gene that encodes one protein in the complex is mutated the complex suffers a substantial loss of activity This type of mutation is classified as dominant negative c Incomplete Dominance i Example 1 loss of function allele 1 A trait exhibits incomplete dominance If one of the two alleles is a loss of function allele a reasonable molecular explanation would be 50 of the functional protein is not enough to give the same phenotype as 100 a heterozygote will give an intermediate trait that is neither dominant nor recessive ii Example 2 probability 1 It has been demonstrated that flower color in four o clocks shows incomplete dominance When two pink flowered four o clocks are crossed to each other what are the following probabilities of the offspring a A plant will be red flowered 25 genotype RR b A plant will be either white or pink 75 genotype Rr or rr d Overdominance i An example of overdomiance would be two lines of true breeding tomatoes that are susceptible to verticillium wilt a fungal infection produce offspring that are resistant to verticillium wilt e Complementation i Two different strains of plant exhibit a recessive phenotype of white flowers When crossed they produce offspring with wild type flowers This phenomenon is called complementation and it indicates that the recessive alleles are in two different genes Environmental Effects a You are trying to develop true breeding blue hydrangeas but the plants in one corner of your plot consistently turn pink regardless of your mating strategy The V VI VII cause of this would be environmental effects because it the phenotype of the flowers is resulting from the physical location of the flowers in the plot Penetrance a What does is mean that a disease is 80 penetrant i This means that only 80 of the people who carry the dominant allele display the phenotype It is important to specify that it is the dominant allele that is not expressed Chromosomes a Homologous Chromosomes the two copies pair of the same chromosome in a diploid cell One is inherited from the mother and the other from the father They are similar but are not necessarily identical because they can contain different alleles b Chromatids these are the chromosomes after replication One chromatid has the same amount of DNA as a single chromosome c Sister Chromatids after the chromosomes have replicated the two chromatids remain attached at the centromere and are called sister chromatids Sister chromatids have twice the amount of DNA as a single chromosome d Bivalent formed when both pairs of sister chromatids associate with each other Bivalents have four times the amount of DNA as a single chromosome e Karyotype an organized representation of the chromosomes within a cell X linked recessive inheritance a Red green color blindness is inherited as an x linked recessive trait i Example 1 What is the probability that a woman with phenotypically normal parents and a color blind brother will have a color blind son with a man who is not color blind they have not yet had any children 1 Because the woman s brother is color blind but her father is not then the mother must have been a heterozygote She therefore has a 50 probability of inheriting the affected allele The probability that she would pass this on to a child would be 50 and the probability that she will have a son is 50 so the overall probability is 0 5 x 0 5 x 0 5 12 5 ii Example 2 What is the probability that a phenotypically normal woman who has already had one color blind son with a man who is not color blind will have a color blind son with the same man 1 Because she has already had one color blind son we know that she is a heterozygote The probability that she will pass it on to her children is 50 and the