Genetics Week Four
Genetics Week Four BIO310
Virginia Commonwealth University
Popular in Genetics
Popular in BIO
This 9 page Class Notes was uploaded by Jayda Abrams on Saturday September 24, 2016. The Class Notes belongs to BIO310 at Virginia Commonwealth University taught by Dr. Wu in Fall 2016. Since its upload, it has received 28 views. For similar materials see Genetics in BIO at Virginia Commonwealth University.
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Date Created: 09/24/16
Genetics Week Three Notes 9/19/2016 Information from the Power Point = Blue Verbal information = Light blue 3.7 Laws of Probability We use statics! This helps with breeding! Sum law: calculates probability of outcomes independent of each other Product Law- In a coin toss it’s the chance of head vs tails. Chance 1 head, 1 tails Binomial theorem: Calculates probability of alternative ways to achieve combination of events n Expression of binomial theorem: (a b) 1 (N= number of events) Monohybrid cross gives one to one. ***Know about Pascal’s Triangle*** 3.8 Chi Squared Chi-square analysis- Evaluates influence of chance on genetic data. Chi- Square analysis- Math conclusion of your conclusion and the expectation and how it matches the real world. Chance deviation- Chance events subject to random fluctuations. Expected outcome is diminished by larger sample size Two factors in analyzing or predicting genetic outcomes: 1. Independent assortment- Subject to random fluctuations due to chance deviations 2. Sample size- Average deviation decreases as sample size increases. Bigger samples are more accurate. Null hypothesis Assumes data will fit given ratio Assumes there is no real difference between measured values and predicted values Apparent difference attributed purely to chance Chi-square ( ) Goodness of fit of null hypothesis- Analysis used to test how well the data fit the null hypothesis. Analysis of observed vs. expected deviations Degrees of freedom (df) Equal to n 1 n number of different categories into which data points may fall (different outcomes) 3:1 ratio: n 2 df 1 9:3:3:1 ratio: n 4 df 3 2 When number of degrees of freedom is determined the value can be interpreted in terms of a corresponding probability value (p) 3.9 Pedigree A pedigree is a family tree with respect to given trait that reveals patterns of inheritance of human traits. Pedigree Key Circle female Square male Diamond unknown sex Parents connected by single horizontal line Offspring stem off vertical line from parent Double line related parents, such as two cousins (“consanguineous”) Twins= Diagonal lines stemming from vertical line connected to the sibship line Identical (monozygotic) twins= Diagonal lines are linked by horizontal line Fraternal (dizygotic) twins= Lack this connecting line 3.10 Mutant Phenotypes Mendel’s wrinkled peas: molecular explanation SBEI: Starch-branching enzyme Catalyzes formation of branched starch molecules as seed matures Wrinkled peas lack this enzyme Osmotic pressure rises wrinkled peas Chapter 4 Intro Genes are like people they don’t always go along with everything and they can interact with each other. When genes interact different outcomes occur. 4.1 Alleles Two postulates are basic principles of gene transmission Genes are present on homologous chromosomes Chromosomes segregate and assort independently Gene interaction: single phenotype is affected by more than one set of genes How alleles pair makes different phenotypes. Alleles: Alternative forms of a gene Wild-type (wt) allele: Occurs most frequently in nature and is usually, but not always, dominant Mutation: Ultimate source of alleles New phenotypes result from changes in functional activity of gene product Eliminating enzyme function Changing relative enzyme efficiency Changing overall enzyme function Change the function of other gene(s) Loss of Function Mutation Gain of Function Mutation New phenotype results from change Mutation enhances function of wild in activity type Mutation causes loss of wild-type Quantity of gene product increases function Genes are double stranded DNA Large = 100,000 Base pairs Small =Less than 1,000 pairs 4.2 Symbols for Alleles Dominant alleles indicated by either an italic uppercase letter (D) or letters (Wr) Recessive alleles indicated by either an italic lowercase letter (d) or an italic letter or group of letters with the superscript (Wr ) when the mutant type is dominant (upper case) 4.3 Types of Dominance Incomplete or partial dominance Intermediate phenotype Neither allele is dominant Two genes expressed the same amount is incomplete dominance/ partial dominance. Incomplete dominance in humans- Example: Tay-Sachs disease: Homozygous recessives affected by fatal lipid-storage disorder Disorder fatal for neonates Hexosaminidasem A activity absent Enzyme involved in lipid metabolism Normal heterozygotes: One copy of mutant gene 1/2 wt enzyme activity compared to homozygous normal non-carriers Threshold effect Normal phenotypic expression results Certain level (usually 50% or less) of gene product is attained In Tay-Sachs disease, 50% threshold 4.4 Codominance Codominance No dominant or recessive No incomplete or blending Joint expression of both alleles in a heterozygote Codominance- neither is dominant or recessive and more than one trait is shown at their full potential, there is no blending. (Example: Blood Type) MN Blood Group an individual may exhibit either one or both antigenic glycoproteins present on the surface of red blood cells. Both capitalized means both are dominant and completely expressed. 4.5 Multiple Alleles of a Gene May Exist in a Population Every gene can only have two forms, but many different forms exist. Alleles only allow two forms. Multiple alleles Three or more alleles of the same gene Resulting mode of inheritance unique Can only be studied in populations How Blood Types Are Created: Everything is free to segregate and recombine. 3 forms of a gene creates 4 different phenotypes: A, AB, B, and O. Human ABO blood groups Example of multiple alleles A and B antigens present on surface of red blood cells Three alleles of a single gene responsible for ABO phenotypes Three alleles designed: A o I allele B o I allele o i allele I and I allele: Produce their respective antigens i allele: Does not produce antigen I and I are dominant to i A B I and I are codominant to each other A and B antigens o Carbohydrate groups bound to lipid groups on red blood cells H substance o One or two terminal sugars are added o O blood types (ii) only have the H substance protruding from red blood cells 4.6 Essential Genes! Humans have about 21,000 genes but they are not all essential. Only 1/3 (7,000) of the genes are essential. How do we know what is essential? Something is essential if it is required for life and survival. Mutations can be tolerated if heterozygous One wild-type allele sufficient for survival Homozygous recessive will not survive Mutation behaves as recessive lethal allele Lethal allele Has potential to cause death of organism Alleles are result of mutations in essential genes Inherited in recessive manner You do not see people with lethal genes walking around, they are dead Dominant lethal allele Presence of one copy of allele results in death Huntington disease 50/50 from parents Dominant autosomal allele H Onset of disease in heterozygous delayed until adulthood Characterized by progressive degeneration of nervous system, dementia, and early death Knockout- Change base or delete it to stop gene from working to see what it does. Agouti gene in mice (coat color) Agouti allele A Mutant yellow allele A Y Mutant allele (A ) Behaves dominantly to normal allele to control coat color Behaves as homozygous recessive lethal allele Genotype A A does not survive 4.7 Two Modes of Inheritance Everything is free to segregate and recombine, this is not limited to dominant and recessive. Different modes of inheritance combined Results in many variants of modified ratios Example: Two heterozygotes mate Both autosomal recessive for albinism Both blood type AB Albinism inherited Mendelian style A B Blood types via three multiple alleles, I , I , and ii 4.8 …More than One Gene Several genes can interact and results in many things. Phenotypic characters are influenced by many different genes and their products Gene interaction Several genes influence a particular characteristic Cellular function of numerous gene products contributes to development of common phenotype Expression of one gene can affect the expression of another gene.= epistasis Epistasis Expression of one gene masks/modifies effect of another gene pair Gene masks phenotypic effects of another gene Each step of development increases complexity of organ Under control and influence of many genes Epistasis and multiple gene interaction: Hereditary deafness Ear forms as result of many genes Genes interact to produce common phenotype Mutations interrupt development hereditary deafness Mutant phenotype (heterozygous trait) Bombay Pedigree- For O both parents need to carry i. How can they combine? Where does the i come from? If the FUT1 given is broken or mutated you will get a mutation that cannot be added to anything. Bombay phenotype Type O female, yet… – one parent has type AB blood and B – female is I allele donor to two children Female found to be homozygous for FUT1 at the fucosyl transferase locus – Prevents her from producing normal H substance – No substrate to make A or B antigens – Results functionally in type O Bombay phenotype – Homozygous recessive condition – First locus masks expression of second locus A B – Mutant FUT1 gene masks expression of I and I alleles – A and B antigen forms only when individual has one wild-type allele Gene interaction reveals inheritance patterns Epistasis has effect on one or more of four phenotypic categories (Figure 4-7) Recessive epistasis – B allele: black pigment – A allele: agouti phenotype – aa genotype: all black – bb genotype: no black pigment, even if A or a alleles present Mouse is albino – bb genotype MASKS expression of A allele recessive epistasis Dominant epistasis – Dominant allele at one loci masks an allele at second loci Example: Summer squash fruit color Dominant allele A White fruit Regardless of second loci allele Absence of A allele Yellow fruit Genotypes aa, BB, Bb yellow fruit Genotype bb green Disc-shaped fruit (AABB) crossed with long fruit (aabb) F 1 all disc-shaped fruit F 2 includes parental phenotypes and spherical variants in 9:6:1 ratio 9/16 A-B- disc (dominant alleles at both loci) 3/16 A-bb sphere, 3/16 aaB- sphere(dominant allele at one/either locus) 1/16 aabb long (no dominant alleles)
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