BIO207 - Introductory Genetics

Genetic discoveries timeline First discovered in 1865 by mendel Crystal structure known at 1940. Didn't know it was hereditary material yet Technique with which u crystallize molecules, x-ray them, and based on diffraction of different rays, you are able to infer structures After 1940 → watson and crick: figured out helix structure. In 1955 1960 discovered transcription and translation 2001 → able to publish sequence for human genome Testing the blending theory of inheritance Once get interme

Intro GG is because probability of obtaining G from Gg = Probability of getting yellow seeds is sum of all 3. + + Hypothesis test 1 To check if mendel's law of segregation applies or not - test cross Working with pure breeding round. Crossing them with pure breeding wrinkled Any time we cross a homozygous recessive → test cross This is the pattern that he say from test crossing: If alleles truly segregate, F1 must he heterozygous. The fat that F1 is heterozygous tells us segregation

Rejected blended theory Realized there was some ratio that kept occuring. It was the 3:1 ratio. Used it to formulate further explanations. Realized that 3:1 ratio could help him figure out whether segregation was occurring and how formulated random segregation and random union. Tested random segregation and union. Test cross - Start with pure breeding parents get F1 and followed by test cross. Test 2-Self fertilization - The only way that these observations would be explained is if random se

How does he know whether he got close enough to expected? Use chi square test Genotype determines phenotypes of whole plant. When planted, can look at phenotypes. Gametes are peas Parent x parent Those are gametes (unfertilized) of parent. Then they got fertilized-zygote. Those can planted and those are now fertilized gametes again Female and male gamete-fertilization-zygote-1 genotype How to produce full plant Through cell division. Making copies of cell and all have RR with one exceptio

Chi square test Used for comparing 2 groups together. Measure of global diff of everything we compared. Want to convert it to a prob that the diff arising from expected and observed is due to random fluke What is prob that they are very similar and diff is due to random chance? High prob → these diff are very little and are not significant. chi square increases as you move to the right side of the table. This means the bigger the diff (chi value), and P value decreases. Comparing 8 groups 90%

Genes and Chromosomes Genes Particles of inheritance Comes in diff forms Unit that is getting passed on from one generation to next Physical unit It is a DNA sequence, a molecule Not a stand alone molecule Alleles for the same gene Polymer is same, but building blocks are not identical in terms of sequence Ie in one allele AGGGG, in another allele, ACCCCC That sequence diff, gave 2 alleles for 1 gene More than allele for particular gene-differ in nitrogenous bases Genome - Complete set of g

1) This is one chromosome and have genes pointing in different directions. how can they be transcribed in diff directions? BRCA transcribed to left where's RPL transcribed to right. Is that possible? A template strand depends on which gene we are working with. For one gene on chromosome, template strand might be bottom, and for other gene, it might be upper one. Therefore, diff genes can be transcribed in opposite directions Is it possible now I can have another gene within that being transcrib

Genotypes Gametes is going to have 1 of the letters. Looking at whole genome-diploid. In gamete-haploid. Chromosome 21 have 1 paternal and 1 maternal. Every gamete → 1 chromosome 21. For every chromosome pair (maternal and paternal are homologs) → For every chromosome type → End up with half the number of chromosomes in gametes. It is n. Germ lines cells-precursor from which gametes are generated. Those precursors-diploid → The ancestors of gametes Undergo meiotic cell division and go haploid

Codominance When in heterozygous state, when phenotype of neither homo wildtype or homozygous new allele, have new phenotype don’t have full dominance relationship. Partial dominance intermediate phenotype Example of codominance-blood type Codominance → both phenotypes are present those of both allele In partial dominance (or intermediate) → see something in between In blood types → Type AB → codominance. Both coexist. Have more than one allele and don't have same dominance relationship. Wild-

Distortions in allelic rations Distortions are a result of mutations that are lethal. Expect appearance of certain phenotypic categories/classes at certain ratios. Sometimes don't see all of these categories Lethality of certain genotypes Looking at wild type phenotype whereas other as a result of 2 genotypes crosses together. e cross: 3:1 ratio. When plants, ¼ recessive. Have lethality of homozygous recessive genotype What is the evolutionary reasoning behind persistence of these lethal alle

Extensions of Mendelian inheritance Gene products work in interconnected pathways One gene can mask genotypes of another gene Epistasis - Seen through 2 individuals have same genotype at specific gene, their phenotype might be diff due to genotype at diff locus Variable expressivity - One genotype doesn't mean can produce 1 phenotype: can have varying degrees of intensity and variation depends on other factors such as other genes, environment, their interactions penetrance - Genotype might not p

Complementation analysis We have ability to mutagenize certain loci within genome and can do randomly because these mutagens don't have the specificity to go into certain areas of the choice Used genetic crosses to create pure breeding mutant lines Unknown mutation for 1 and 2 pure breeding mutant line Are they all in same or diff genes? Test is a diagnostic to figure out if 2 diff mutations are on same gene or not If mutations fall on the same gene: not gonna get complementation because both m

Genetic Linkage See multiple loci/genes and they contribute to diff phenotypes. Sometimes these phenotypes are related. Yellow region associated with certain shape of antenna in fruit fly. In mutant, see antenna looks diff. Another region (orange), when look at wild type and homozygous mutant, see diff phenotype of wings. Have multiple genes and gene products that can contribute to one phenotype, and in this case is wild type wings Point - Illustrating with which we have info chromosome each c

There are multiple configurations in meiosis that allow for crossing over When have syntenic genes Genes are located on same chromosomes that are fairly close together, crossing over will occur. But it involves a lot of machinery The closer 2 genes are, the more difficult for crossing over to occur but the machinery is more jammed Due to distance limitation, not a 50/50 chance whether crossing over happens or not. It is more unlikely for it to happen. That;s why see more chromosomes that have

Morgan's crosses Imp of genetic cross that can be done in order to uncover recombination frequencies. If a cross is designed in a specific way, the phenotype of offspring can give info about genotype of gametes. Recombinant gametes found at a lower frequency given certain conditions These are just gametes. In order to figure out genotype, we test cross. male hemizygous equivalent to test crossing Quantitative Look at observed number of progeny and see that if we were to look at all males and

Cross designed to illustrate crossing over between 3 genes If no crossing over, we would expect equal frequencies for each category, if mendelian laws were to apply. Why? Since we have random segregation and random union, there is no preference for any of the gametes and expect all of them to occur at equal frequencies. Another way, for each locus, a heterozygous x homozygous recessive. So if have Aa test crossed, would expect 50/50 for each phenotype. And same for next locus and so on. No pre

Phenotypic variation See variation This type of phenotypic variation is not discontinuous Before we had discontinuous, 3:1 ratio, 9:3:3:1 ratios. These concrete classes-discontinuous variations What we are seeing in image is continuous variation The size of tomatoes can vary have a continuous spectrum of phenotypes We call these continuous traits quantitative traits the reason why we don't see this discreteness and category is because we have so many genes doing the work to produce final ph

Quantitative traits - Additive effects We know we have quantitative traits that display continuous spectrum of phenotypes, rather than discrete. Why does this happen? Even though mendelian laws still apply, we see the increase in number of phenotypes because of the nature of these alleles and how they contribute to phenotypes Monohybrid crosses to itself and see usual 3 categories. 2 loci → and we automatically see number of phenotypes increasing We are seeing translation of discrete categorie

Heritability Looking for genetic variation that is contributing to phenotypic variation Giving idea how much genes is contributing to phenotype It differs from trait to trait 2 types of heritability we can measure Broad sense heritability - Total genetic contribution to phenotype Narrow sense heritability - Look at the additive component of genetic contribution. How much of the total phenotypic variation, how much is additive. Why additive? Additive genetic variance is of a lot of interest usual