Genetics Exam 2 Study Guide
Genetics Exam 2 Study Guide BSCI - 30156 - 002
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BSCI - 30156 - 002
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This 6 page Study Guide was uploaded by Jessica Brown on Monday March 7, 2016. The Study Guide belongs to BSCI - 30156 - 002 at Kent State University taught by Chi-hua Groff (P) in Fall 2015. Since its upload, it has received 58 views. For similar materials see ELEMENTS OF GENETICS in Biological Sciences at Kent State University.
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Date Created: 03/07/16
Genetics Exam 2 Study Guide Highlight= Vocab word Highlight= important information Highlight=formula Important Vocabulary Genetic Map: a diagram that describes the order of genes along a chromosome. Synteny: two or more genes are located on the same chromosome Genetic Linkage: phenomenon in which genes that are close together on the same chromosome tend to be transmitted as a unit Linkage Groups: physically linked genes on a chromosome Locus: the site where the gene is found on a particular chromosome Complex Traits: characteristics that are determined by several genes and are significantly influences by environmental factors Quantitative Traits: continuous traits that do not fall into discrete categories. Typically are complex traits. Heritability: the amount of a phenotypic variation within a group of individuals that is due to the genetic variation Pleiotropy: Multiple effects of a single gene on the phenotype Epistasis: Several genes interacting on a single loci Linkage Chromosomes consist of several genes (hundreds to thousands) o Position and order of these genes on each chromosome is retained throughout the entire species Blocks of genes that are ordered in the same way and are conserved across different species as a result of shared ancestry are known as syntenic groups Chromosomes are known as linkage groups o This is because genes on a chromosome are physically connected to each other Linkage violates Mendel’s law of independent assortment o Genes that are close together are transmitted from parent to offspring as a group This is the reason Mendel’s law is violated o Genes that are father apart tend to assort independently due to crossing over This is true to Mendel’s Law o Bateson and Punnett were the first to demonstrate that two traits do not always assort independently They discovered this by doing crosses with sweet pea flowers o Morgan and Sturevant discovered that some crosses did not match the expected phenotypic ratios of unlinked genes Maximum recombination frequency is 50% Linkage and Crossing Over Crossing over: an event that occurs in prophase 1 of meiosis 1 where sister chromatids of one pair cross over with the sister chromatid of the other pair. o Creates new combinations of alleles The combinations that are identical to the parents are called parentals The combinations that are different then the parentals are called recombinants Morgan studied X-Linked patterns of inheritance o He did this experiment using three traits; body color, eye color, and wing shape. o It expected there would be 8 equally proportioned phenotypic classes if the three traits sorted independently Results: A majority of offspring had the same combination of alleles as the parents (these are deemed parentals or nonrecombinants) Morgan suggested that these three traits are found on the X chromosome and are inherited together as a unit Results: offspring not containing the same combination of alleles as the parentals (recombinants) Morgan suggested that there was crossing over between homologous X chromosomes o Morgans 3 Hypotheses 1. All three genes are located on the same (X) chromosome 2. Crossing over produces a new combination of alleles (recombinants) 3. Crossing over is highly dependent on the distance between two genes on a chromosome The farther apart the genes the more likely they are to cross over The closer together the genes are the more likely they are to travel as a unit (following Mendel’s rules) Genetic Mapping Allows us to determine distances between genes thus allowing us to predict the probability of crossing over occurring o Genetic distance is different than physical distance Genetic and physical distance are related but different o Genetic distance and recombinant offspring amount is a directly proportional event To create a genetic linkage map a testcross must be utilized (see previous exam material if you are unsure of how to do a test cross.) o Test cross allows us to be able to distinctly distinguish recombinant and nonrecombinant offspring Recombinant offspring are typically the ones with the lowest number/amount of offspring number of recombinant offspring Map distance= x100 total numberof offpsring o Total=recombinant and nonrecombinant offspring o Units for map distance is either centimorgans (cM) or map unit (mu) o One mu/cM= 1% recombination frequency Trihybrid (three gene) Crosses Used to determine the order of genes and the distance (map units or centamorgans) the genes are from each other Producing a three gene cross o Cross two true-breeding strains that differ in their 3 alleles These are your parents o Perform a test cross from the F1 generation that you got from breeding the parents o Collect the data for the F2 generation The parental (nonrecombinants) should be the largest numbers These are good for genetic mapping because they’re easy to follow Single crossovers should be the second lowest numbers Double crossovers will be the lowest numbers Must use the double crossover and parents to determine which gene is in the middle Calculate the map distance Show your calculations in a map Interference: can influence the number of double crossovers that tend to occur in a short region o Map distances=recombination frequency This gives you the expected amount of double crossovers The probability of a double crossover = the recombination frequency between genes The probability when multiplied by the total number of offspring should equal the observed number of double crossovers However, it is rare that this actually occurs because of positive interference Positive interference: when a crossover occurs in one area of a chromosome , it decreases the probability that a second crossover will occur in that same area Be sure to practice 3 gene crosses and all the calculations that go along with that! Chi Square Statistic that helps us to understand if genes follow Mendelian inheritance or not Degrees of Freedom= (number of groups)-1 Null hypothesis: no different between expected and observed o Chi value > statistic Reject o Chi value < statistic Accept Be sure to understand the concept of this, don’t worry so much about calculating Quantitative Traits 1. Have continuous distributions a. This means the trait isn’t one or the other. It can have a ton of variation and in betweens. Think of height. 2. Affected by many genes 3. Many human diseases fall into this category a. Multifactorial Quantitative Trait Loci (QTL): a region of a chromosome containing one or several genes Mapping QTL’s is a strategy for identifying genomic regions that underlie trait(s) Some traits are controlled by just a few QTL’s but others can be under the influence of multiple QTL’s Phenotype Phenotypic traits are traits that can be observed and quantified. o Most of them are polygenic: influenced by more than one gene o Genetics isn’t the only thing that contributes to the phenotype, we must also account for environmental factors Phenotypic Plasticity: a single genotype that may produce different phenotypes in different environments. (ability to vary) Epistasis: interaction between two or more genes that influence the same phenotypic trait. o These traits can work together to be beneficial, go against each other to be deleterious or cause each other to be neutral Pleiotropy: one gene influences several different phenotypic traits o Master regulator genes are an example of a pleiotropic gene Be sure to know and understand the difference between epistasis and pleiotropy. This will be important for the exam!! Variance Phenotypic variance: (V oP V ) The sum of the differences of the genetic variance (VG)and the environmental variance (V ) E V =V +V P G E Genetic Variance (V )G split into additive genetic variance (V )Aand dominance genetic variance (V )D V GV +A D Additive variance is the variance in a trait that is due to each individual allele being added together, without interference or interaction from any other alleles. They are epistasis interactions Dominance Variance is the variance due to interactions between alleles o They can interact to make a trait greater or lesser then the sum of the two alleles acting alone o Not directly inherited from parent to offspring Therefore, we can infer V =PV +VA+V D E When it comes to these calculations—be sure to understand what it means and why you use that calculation. Dr.Chiu cares more about your concept understanding then your math skills! Heritability Heritability: the sum of how much variation of a trait is due to genetic factors as opposed to environmental factors Two specific types of heritability can be calculated o Broad Sense Heritability (H )2 H =V /GV P 2 o Narrow Sense Heritability (h ) The proportion of variability that can be passed on from parent to offspring 2 h = V A V p If h = 0 o The variance is due entirely to additive effects (environmental) and the offspring will not closely resemble parents (for the trait of interest) 2 If h = 1 o The variance is due entirely to heritable differences (genetics) and offspring closely resemble parents Values of 0 and 1 are extremely rare. Most often the number falls somewhere between these numbers Heritability describes the amount of phenotypic variation due to genetic variation for a particular population raised in a particular environment o The results for the given trait in a given population can (and will) change when tested in another population Correlated Selection: independent genetic variation in two or more traits. Out of these traits selection favors some combinations of character states over others This of the snake example o Color patterns of snake and their escape speed (pleiotropy) Norms of Reaction: a species with a similar genome that have different phenotypes Shows how a genotype acts to an environment Plasticity: Identical genomes acting differently to different environments If people react differently to different environments then other people we can safely assume that there is a genotype/environment interaction Selective Breeding Most common way of estimating narrow sense heritability (h ) 2 Can aid in predicting the outcome of selective breeding News and Views Article Experimented on yeast Environment can be set to zero for individual plates Larger spots progeny inherited genotype that is well suited to survive to adverse environment Smaller spots progeny inherited genotype that is NOT well suited to survive in an adverse environment This experiment showed that there was in fact “missing heritability” in humans If you have not read this article, it is advised that you do, she will ask about it on the exam! Epigenetics: external modifications of DNA Such as methylation and demethylation to silence and activate genes Heterochromatin: silent DNA and heavily methylated o The methylated nucleotide in DNA is cytosine o Methylated nucleotide in RNA is adenine Non methylated DNA= gene expression or activation (euchromatin) Methylated DNA= gene silencing (heterochromatin)
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