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Cue card midterm 2.docx

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University of Ottawa
Colin Montpetit

Lecture1: Diploid: (2n)A condition in which each chromosome exists in pairs; having two of each chromosome called homologous chromosomes. Haploid: (n) A cell or an organism having one member of each pair of homologous chromosomes. Also referred to as the gametic chromosome number. Meiosis: (to halve the ploidy for gametes)The process of cell division in gametogenesis or sporogenesis during which the diploid number of chromosomes is reduced to the haploid number. Meiosis is associated with gamete formation. Cells produced by meiosis receive only one chromsomes from each chromosomes pair, in which case the resulting number of chrosmosomes is called the haploid number. Fusion—zygote. Stages of meiosis: In meiosis one, homologous chromosomes (1 strand) come together and join by cohesins (into 2 strands), which then duplicate to form tetrads (4 chromatid groups). At this point crossing over occurs, chromosomes are held together against tension. At the end of Stage 1, n = half. At end of meiosis II, the 2 sisters are split to 1 chromatid per cell (from the sister pair). Homologous chromosomes: Chromosomes that synapse or pair during meiosis and that are identical with respect to their genetic loci and centromere placement Gametes: A specialized reproductive cell with a haploid number of chromosomes Chiasma: (pl., chiasmata) The crossed strands of non-sister chromatids seen in diplotene of the first meiotic division. Regarded as the cytological evidence for exchange of chromo-somal material, or crossing over. The point of crossing over.SRY gene: The sex-determining region of the Y chromosome, found near the chromosome’s pseudoautosomal boundary. Accumulated evidence indicates that this gene’s product is the testis- determining factor. At 6-8 weeks it becomes active and releases TDF in embryonic development. With no SRY gene gonads develops as ovaries by default. Euploidy: it’s a defect in the chromosome number. It is the addition of loss of complete sets of chromosomes (1N missing, 2N, etc). Ex: evolutionary changes! Aneuploid: does not involve whole sets-nondisjunction. Incomplete (unbalanced chromosome sets ex: monosomy (2N-1): turner syndrome, trisonomy (2N+1): 21-down syndrome. May cause LOF if threshold isn’t reached by one 1 allele. Structural aberrations: Chromosomal rearrangements and deletions: translocations (part of the chromosome gets cut off and gets incorporated on another chromosome., inversions (a piece can break apart and when it gets repaired it gets repaired upside down), deletions (bits can get eliminated). They can happen during crossing over. Complete Gene linkage: two genes on a single pair of homologs: no change occurs. Assortment of genes not independent, genes on the same chromosome. Crossing over linkage: two genes on a single pair of homologs, exchange occurs between two non-sister chromatids. Produces recombinant gametes. (A-B on same chromosome for mom and a-b for dad, when crossing over occurs there will be 2 non crossed over (A-B and a-b) but also cross over where the linkage was on 2 sister chromatids from each) Frequency of CO proportional to distance between two genes. Nondisjunction: The failure of homologous chromosomes to separate normally during nuclear division. Two types: Meiosis I: homologous pairs do not separate and there you get an extra chromosome for the first two cells (trisonomy, minosomy). Meisosis II: meiosis I occurs normally but sister chromatids do not separate properly so you have 2 normal chrosomeos and 2 defective. Rate increases with age, more in women because less energy is used to maintain the egg cells. Lecture2: Forward genetic analysis: Investigators interested in studying the genetics of a trait but has no evidence that the trait is genetically based (therefore performing crosses would help resolve the question). This approach is also very useful if for a given trait, there is no variance in the population. You would induce mutations to create the variance. (Target gonads, need every cell to contain mutation in the offspring. After mutation, screen for mutants and get rid of wilds). As the interest is to study the genetic nature of the trait (if any), then the variance will help you design experiments to detect whether or not the trait is transmissible from one generation to the other, thus confirming the heritability of the trait and opportunities to map it in the genome.Reverse genetics: Typically, investigators have already a clue of the sequence for the trait they are interested in studying. Now the idea is to cause targeted mutations within that gene. By modifying the gene, one can then gain a sense of the role of the gene. is an approach to discovering the function of a gene by analyzing the phenotypic effects of specific gene sequences obtained by DNA sequencing. This investigative process proceeds in the opposite direction of so-called forward genetic screens of classical genetics. Simply put, while forward genetics seeks to find the genetic basis of a phenotype or trait, reverse genetics seeks to find what phenotypes arise as a result of particular genes.Putative geneinduce mutations (targeted)screen variantsgene function. Functional genetics: Model organism: is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the organism model will provide insight into the workings of other organisms. Good model organisms have fast reproduction, maturation, numbers, etc. Also cool traits because they are good to study. LOF: Mutations that produce alleles that encode proteins with reduced or no function mutations result in a protein that has little or no enzymatic activity. Most mutations are associated with LOF because many changes that affect the normal 3 surtde would disrupt the active site (even if the mutation affects an AA that is fra away from the active site) and most are recessive because half the amount of wilde type gene product is usually suffient to give a wild tppe phenotype GOF: A mutation that produces a phe- notype different from that of the normal allele and from any loss of function alleles. Gain of function of mutation change the gene product such that it gains a new function or enhanced function.Its mutations result in a functional protein that is made at the wrong place, time and has a new activity These mutations are usually dominant phenotypes. {loss of a regulatory Genetic markers: A variation (which may arise due to mutation or alteration in the genomic loci ) that can be observed. They are inherited variations that are used to test genetic hypothesis. By tracking marker, we are tracking chromosome. Visible markers: (outwardly expressd phenotypes)Biochemical markers: (e.g. protein variation)Molecular markers: is a fragment of DNA that is associated with a certain location within the genome. Molecular markers are used in molecular biology and biotechnology to identify a particular sequence of DNA in a pool of unknown DNA.Morphological markers: (score gender and differences in structures)Behavioural markers: (score behavioral traits) ex: mice visual inspection, wheel running etc..Lethal mutations: are mutations that lead to the death of the organisms which carry the mutations in recessive, often have a phenotypic expression in hetero condition (short cat tail). Conditional mutations: (score based restrictive and permissive conditions) mutation that has the wild type phenotype under certain conditions and a mutant phenotype under other conditions Ex: Siamese cats. Heat and other stresses can cause a complex molecule like DNA to denature, or lose its function due to the unfolding of its three-dimensional structure. In the denaturation of double-stranded DNA, the hydrogen bonds of the duplex structure break, the helix unwinds, and the strand separate. (midpoint = melting temp) and they single strands of nucleic acid can reform.Nutritional mutations: (score based nutritional needs) ex: prototroph vs. auxotroph’s. Humans are auxotrophic for vitamin c. auxotrophic mutants for adenine and leucine in E.coli. Resistance mutations: (score based on resistance to drugs) Mutations which confer resistance to a specific compound ex: bacteria, antibiotics such as penicillin. Phenotypic ratio: ratio of the physical appearance that show the different outcomes you can get in a cross Genotypic ratio: ratio of the combination of alleles Pure line: a population that breeds true for a particular trait. A homogenous line of descent. Reciprocal cross: hybridization involving a pair of crosses that reverse the sexes associated with each genotype. Its designed to test the role of parental sex on a given inheritance pattern. Test cross: A cross between an individual whose genotype at one or more loci may be unknown and an individual who is homozygous recessive for the gene or genes in question. (Aa/AA – unknown, cross with aa): If AA, all will be dominant phenotype, if not – ½ (1:1). Backcrosses: Performed for dominant mutations. First induce mutation (BB->Bb). Cross mutant (Bb) with a wild type (BB) for F1 generation of heterozygote (Bb), now keep crossing (Bb parent with Bb F1 until a bb is achieved). Bb and bb must have distinct phenotypes (grey mice and black mice). First reason is that you want to introduce an allele into a genetic background of another individual, it is easier and cheaper than crossing with another organism. Polymorphism: The existence of two or more discontinuous, segregating phenotypes in a population. (genetic basis for variation is not easy to determine, may be a protein and not an observable phenotype). If we are studying humans, we must use large families so we can see variations from the pedigree. Chromosome theory of inheritance: Genes are located on chromosomes and that the behavior of chromosomes during meiosis accounts for inheritance patents: the two laws biochemical polymorphism - the occurrence of the varieties attributed to biochemical difference, which are under genetic control. A population is said to exhibit genetic polymorphism when two or more distinct inherited varieties co-exsited in the same individuals. A genetic character is now to be polymorphic when the rearest phenotype has a frequency greater than one percent. (example sickle cell haemoglobin trait) Crosses: When doing crosses, always start with pure lines (AABB/aabb, or AAbb/aaBB to get heterozygotes in F1) Monohybrid cross: is a cross between F1 offspring of two individuals that differ in one particular trait. Ex: color of eyes. Ee x Ee. If you get a PR 3:1 ratio then you know you have dominant and recessive allels that are obeying the law of segregation and assortment. GR: 1EE:2:Ee:1:ee. Deviations :1:2(hetero):1 = codominance; 2(hetero):1 = lethat; 1:2(hetero):1 = incomplete dominance; sex linkage anything else dihybrid cross- is a cross between F off1pring of two individuals that differ in two traits of particular interest. Example ( Bb x Bb). It is often used to test dominant and recessive genes in two separate characteristics. (e.g., yellow, round * green, wrinkled peas). If you get a 9wildtype:3wildtype for one gene and mutant fr the other3:1: mutant for both genes. Deviations: 9:3:4 (recessive) or 12:3:1 (dominant) = epistasis; 13:3 supression; 15:1 duplicate gene, 9:7 complementary.trihybrid cross- the mating of two individuals, organisms, or strains that have different gene pairs that determine three specific traits or in which three particular characteristics or gene loci are being followed. genes- a unit of heredity that is transferred from a parents to offspring and is held to determine some characteristics of the proteins coded directly by genes. Distinct sequence of nucleotides forming part of DNA. chromosome- is an organized structure of DNA and protein that is found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosome may be circular or linear. alleles- are defined as a
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