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UNC-Chapel Hill BIOC 108 - Unit 3

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Introduction to Genetics: What is Genetics?o The study of genes, genetic variation, and heredity in all living organismso Gene = functional unit of heredity, a heritable traito Alleles = alternative forms of a gene at the same genetic locus (one from each parent)Terms to Know: Histone: protein spool that DNA is wound around to avoid tanglingand to maintain function Have a lot of positive charges that neutralize the negative charges of DNA backbone Chromatin: histone/DNA spools pack closely to form a larger coil that organizes with scaffholding proteins when a cell is not activelydividing  Chromosome: complex between proteins and DNA molecule that is visible during cell division when the DNA becomes highly compacted  Intron: non-protein coding portion of a gene not present in mRNA Exon: protein-coding portion of a gene present in mature mRNA Splicing: removal of introns from RNA to form mature mRNA Homozygous: 2 alleles of a gene/trait are identical Heterozygous: 2 alleles differ for a gene/trait Punnet Square Analysis: predicts probability of genetic events Dominant: visible or measurable traits are dictated by only one of the alleles of a heterozygous individual (allele is dominant) Recessive: a hidden allele  Phenotype: visible/measurable make-up or appearance of an organism Genotype: genetic make-up of that organism, determines the phenotypeMendel’s Principle of Segregation: - There are 2 alleles for each gene at homologous positions on a pair of chromosomes (one from each parent)- The 2 alleles separate to form haploid genesMendel’s Principle of Independent Assortment:- Genes on different chromosomes segregate independently of each other when gametes form, but genes on the same chromosome go together- This means there is random selection of which of the 2 chromosomes in a somatic pair are selected when gametes are formed - Beauty of human diversity!Polymorphism: - Single position in the genome sequence for which 2 or more alternative alleles are present at an appreciable frequency in the human population - Changes in single base pairs that lead to a change in traitHumans have 23 pairs of chromosomes: Most cells in our bodies are somatic cells which are diploido Contain 23 pairs of chromosomes = 46 totalo 22 pairs of autosomes and 2 sex chromosomes (XX or XY) Germ cells form gametes which are haploido Contain 23 chromosomes totalo 22 somatic and 1 sex chromosome (X in eggs or Y in sperm) Genes are located on chromosomesSplicing results in mature mRNA:o Splicing is mediated by small nuclear ribonucleoprotein particles (snRNPs) at splice sites in RNA sequence (can be in introns)o RNA must be spliced before it can leave the nucleus Gene Expression: - Our genome is full of “gene families”o Sequence similaritieso Protein structure similaritieso Protein function similaritiesHow is Gene Expression Regulated within the Human Body? Expression of thousands of genes must be carefully regulatedso the right amounts of the correct proteins are produced at the right time in the right tissues All cells within your body have the same genome Different cell types in multicellular organisms differ in structure and function Therefore, different genes are expressed different sets of mRNA are transcribed and translated into protein within each cell type Different cell types synthesize different sets of proteins:Protein expression is dynamic!Regulation of gene expression occurs at many levels:1. Transcriptional Control: How many copies of RNA are made from DNA Gene silencing – inhibition of transcription by methylation of C in specific CG pairs Transcription factors – proteins that bind to the promotor or enhancer sequences in DNA to promote or enhance RNA production 2. RNA Processing: Splicing, capping, poly-A tail addition3. Export of mRNA from nucleus to cytoplasm (only mature mRNA)4. Translational Control: How many copies of potein made from each mRNA5. mRNA Degradation Control: mRNA stability – how soon is it degraded 6. Post-Translational Control:  Proteins modified after syntheses (proteolytic cleavage) Functional activity is regulated (activators, inhibitors, phosphorylation/dephosphorylation)What makes us different… Polymorphisms!- Single nucleotide polymorphisms (SNP): different at 1 single nucleotide- Most SNPs occur in non-coding regions, so most will not lead to a disorder- If SNP occurs in coding region, protein could be alteredProbability of Inheritance: o 2 alleles: T and t (capital letter = dominant)o 2 phenotypes: Tall (dominant) and short oo Tall = TT and Tto Short = tt o Tall phenotype is produced by 2 different genotypes because T trait is dominanto Short phenotype is produced by 1 genotype o TT and tt = homozygouso Tt = heterozygous 3.2 – What Happens When It Goes Wrong???How can mutated proteins result in disease?» Protein not synthesized: mutation makes early stop codon » Mutant protein is inactive or inefficient = loss of function» Rogue protein – mutant protein does something bad, gain of abnormal function» Mutation protein misfolds – incorrect 3D shape, mistargeted, rapidly degraded Classification of Genetic Disorders: Monogenic Disorders (single gene)o Autosomal recessive  PKU Sickle cell anemia Cystic Fibrosis Tay-Sachso Autosomal Dominant Triplet-repeat disease Huntington’s disease X-linked dominant tooo X-Linked Recessive Hemophelia Color-blindness Lesch-Nyhan Multifactorial Disorders: (different systems combining to create disorder)o Influenced by many genes, environmental and gene-by-environment Diabetes mellitus II Cancer Artherosclerosis Hypertension Schizophrenia Addiction  Manic depression Chromosomal Disorders: (rearrangements of the chromosome, affects multiple genes)o Nondisjunction breakage (f) translocationo Down’s syndromeo Turner’s syndromeo Cancero Burkitt’s lymphoma Detection of Genetic Disorders: Monogenic Disorders: family pedigrees, RFLP (Comes from patient/fetus cells)o We get cells by amniocentesis or chorionic villus sampling Chromosomal Disorders: karyotyping (comes from patient/fetus cells)Amniocentesis: fetal cells are in amniotic fluid (sloughed off fetal skin) can be removed 14-20 weeks into pregnancy, tested for defective genes or chromosomes (RFLP, karyotyping)Chorionic Villus Sampling: fetal cells are removed from the developing placenta, examined andthe


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