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Biological Science
BISC 336
Dr.Sarah Liljegren

8/26/13 Genetics is the study of genes, inheritance patterns, and genetic variation among organisms.  Can affect diseases and mortality o i.e. Cancer progression can be related to genetic makeup  5 different single nucleotide polymorphisms (changes); 5 different DNA changes within different genes that can lead to aggressive prostate cancer A brief history of genetics…  Ex ovo Omnia (all from the egg) o William Harvey - 1651 o Epigenesis: substances present in egg differentiate into adult structures Preformation Theory:  1694: Nicholas Hartsoeker  Each sperm thought to contain a miniature adult o All structures were present and creature just got larger  Female was “dirt” for sperm to grow Cell Theory  1830: Theodor Schwann/Matthias Schleiden  Organisms are made of cells Darwin, Wallace, & Evolution  Natural selection: based on observation that populations consist of more individuals than can be supported  Those w/ heritable traits that enhance survival persist.  A theory without a mechanism until… Gregor Mendel  Experimented w/ pea plants in the monastery garden 1856 – 1863; published his studies in 1866  Determined that flower color (purple vs. white) and other traits were controlled by genes that occur as pairs o Observed that traits segregated in his experiments and concluded that they occur as pairs that could be separated during the act of reproduction Chromosomal Theory of Inheritance  Walter Sutton and Theodor Boveri (early 1900‟s)  Proposed that heritable features (genes) are carried on chromosomes Chromosomes  Eukaryotes are generally diploid (2n)  This means that 1 copy of each chromosome is received from each parent.  Karyotype: set of chromosomes within a eukaryotic cell Chromosomes are copied  Mitosis: replicating cells  Meiosis: making gametes A fertilized human egg has how many chromosomes?  A) 0  B) 11.5  C) 23 * if unfertilized  D) 46 *  E) 92 Structure of DNA  Structure described in 1953 by Watson & Crick  G: Guanine, A: Adenine, T: Thymine, C: Cytosine  DNA is made up of complimentary strands that wrap around each other to form a double helix What are genes made of?  Initial debate: Protein or DNA?  Chromosomes are composed of both! Read C1: debate of protein vs. DNA What is a Gene?  A unit of heredity that consists of a stretch of DNA that codes for protein or RNA chain that has function  (segment of DNA that does something) And Alleles?  Alleles are different variants of a gene.  A single gene can likely have multiple alleles. Genotype vs. Phenotype  Genotype: alleles (DNA sequences) that control a trait  Phenotype: observable features of an organism o i.e. thumb crossing o different phenotypes result from different genotypes First Described fly mutant  Thomas Hunt Morgan, 1910  Red is fly‟s natural eye color  White is a mutant color Why studying model organisms is important  Gene affected in white fly mutant encodes a membrane protein that transports red pigment precursor  This protein is related to CFTR protein that is affected in cystic fibrosis (CFTR is an ion channel that transports chloride) 8/28/13 Model organisms used to study genetics. Why is understanding genetics important?  Personalized medicine ie. pharmacogenetics: how does genetic variation impact a patient‟s drug response?  Commercial testing developed to detect variations in the gene (CYP2C9) that metabolizes warfarin (coumadin), an anti-coagulant used to prevent blood clots Chapter 2: Mitosis & Meiosis Transfer of genetic material  Mitosis: from cell to daughter cells  Meiosis: from parent to offspring Chromosomes: a metaphase preparation and resulting karyotype  Homologous chromosomes: one from dad & one from mom Chromosomes  Sister chromatids: duplicated set that will later separate  Centromere: condensed part of chromosome where sister chromatids are attached; placement is how chromosomes are classified Cell Cycle  Interphase (non-mitosis parts)= G1 + S (DNA synthesis) + G2 (cytoplasm has already doubled by end usually) o Intense metabolic activity for growth of cell o DNA replication occurs prior to mitosis o Chromosomes have duplicated during S phase but are not condensed in Interphase  Mitosis refers to the point where chromosomes are being distributed between the two daughter cells T/F Question DNA Synthesis occurs during mitosis. F Centrioles  Associated w/ spindle fibers used in mitosis and meiosis  Differentiated regions in cell (centrosomes) house pairs of centrioles o These organize the microtubules of spindle fibers to be able to pull the chromosomes apart Spindle Fibers  Microtubule arrays that attach to and move chromosomes during cell division (pull apart sister chromatids) Prophase  Centrioles migrate to opposite sides of cell o where they locate to controls the plain of division  Centrioles organize microtubules into spindle fibers that establish axis for chromosome separation  Chromosomes condense  Nuclear envelope disappears Metaphase  Chromosomes migrate to equatorial plane (=metaphase plate)  Kinetochore forms (protein complex that attaches centromeres to spindle fibers) End of Metaphase  Chromosomes are all lined up along metaphase plate Anaphase  Sister chromatids separate from one another and migrate to opposite poles  Separated sisters = “daughter chromosomes” Telophase & Cytokinesis  Cytoplasm is divided among the two daughter cells  Chromosomes uncoil  Nuclear envelope reforms  Spindle fibers disappear Read how process of mitosis is different for plant cells. Transfer of genetic material  Mitosis duplicate and distribute (2n to Functions of Meiosis  Allows haploid gametes to combine at fertilization so that genome size is maintained at 2n o If this doesn‟t happen properly, disorders can occur  Ie. Down syndrome ( trisomy 21 – 3 copies of chromosome 21)  Introduces GENETIC VARIATION o Unique combinations of parental chromosomes found in gametes o Crossing over (= genetic exchange) between homologous chromosomes pairs results in mosaic chromosomes Problem  17 (Chapter 2) A diploid cell has 3 pairs of homologous chromosomes, each heterozygous (C1, C2; M1, M2; S1 S2).  Q – what chromosome combinations could be present in haploid cells after meiosis? Understanding probability  20. Organism with n=10 (2n=20). What is the probability that a sperm will have all 10 maternal chromosomes?  The probability of getting a maternal chromosome for C1 = 0.5 (50%). What about for maternal C1-C10? Meiosis  (Example of 2 pairs of homologous chromosomes  Homologous chromosomes pair up (=synapsis) and crossing over occurs between non-sister chromatids (in reality, it is both pairs unlike the figure)  Tetrad of 4 chromatids  Meiosis 1: tetrads to dyads  Meiosis 2: dyads to monads 8/30/13 Understanding probability  20. Organism w/ n=10 (2n=20). What is the probability that a sperm will have all 10 maternal chromosomes?  The probability of getting a maternal chromosomes for C1 = 0.5 (50%). What about for maternal C1 – C10?  Answer: 0.5 ^ 10 Cell structure & genetic function  Eukaryotes have chromosomes in membrane structure o Nucleolus – region where rRNA is synthesized o Ribosomes  Complexes of proteins and RNAs  Site where mRNA are translated into proteins  Free in cytosol  Associated w/ ER  Prokaryotes have DNA (as one circular chromosome) just in the cell o No membrane bound organelles o Nucleoid – area where DNA is compacted Mitochondria  Found in plant and animal cells  Site of oxidative respiration  Generate ATP Chloroplast  Found in plant algal, protozoan cells  Produces energy through photosynthesis Chloroplast and Mitochondrial DNA  Each has its own genome separate from chromosomes in nucleus  Duplicate themselves, transcription & translation separate from the nucleus  Mitochondrial DNA entirely maternally inherited  Chloroplast DNA generally maternally inherited Mitochondrial inheritance  Who ingerited great-grandma‟s mitochondrial genome? o 1) D-F, G, L o 2) D –F, G –L o 3) A – C, G – I o 4) D – F, J – L o 5) B, D – F, G, L  Answer: 4 Chapter 3: Mendelian Genetics Gregor Johann Mendel  No knowledge of chromosomes or meiosis  Determined that units of inheritance exist  Was able to predict the behavior of these units: i.e. he was able to anticipate the results of his crosses Mendel followed 7 traits.  Each trait had 2 contrasting forms for these particular traits  Was able to obtain true breeding strains: plants that when self – fertilized produced offspring showing the same form of a particular trait (i.e. all offspring had purple flowers) Simplest experiments  Monohybrid crosses of true-breeding individuals differing in only one trait revealed how that trait is transmitted from generation to generation One of Mendel‟s monohybrid crosses…  F1 plants = 100% yellow o Therefore: yellow is dominant over green  F2 plants = 75% yellow 25% green o (3:1 ratio) Results of Mendel‟s monohybrid crosses:  F1 offspring identical to one parent  But 3:1 ratios observed in F2 generation Reciprocal crosses  Mendel tried his crosses in both directions: the results were not affected by which parent carried a particular form of a trait. o Sometimes that is not the case in more complicated genetics  For example, the yellow form of seed color always dominated the green form in the F1. Mendel‟s Conclusions  Proposed that unit factors (=genes) pass unchanged from one generation to the next and determine the traits expressed. Individuals have a pair (=2 alleles) of each unit factor.  One of the unit factors in a pair dominates the other, which is recessive.  The two unit factors segregate randomly during gamete formation. Wrinkled vs. round  The mutant gene affects a protein involved in starch synthesis o the defect in starch synthesis and if loss of water gives them wrinkled appearance DD x dd parents monohybrid cross Result: all F1 Dd heterozygous offspring are tall. Dd x Dd F1 self-fertilized monohybrid cross Results: F2 offspring are tall and short Genotypic ratio: 1:2:1 Phenotypic ratio: 3:1 Test crosses: can deduce an individual‟s genotype by crossing it to a recessive homozygote. The traits that Mendel studied segregate independently. If genes are considered to be linked, they are inherited together. If they are close to each other on the same chromosome, then Mendel‟s rule is not followed. They won‟t segregate independently. The traits that he studied were far enough away on the same chromosome or on different chromosomes. Read Chi – square Test and monohybrid and dihybrid tests 1000 F2 plants # Expected 750 250 #Observed 740 260 X^2 = sum (o-e)^2/e Number (n) of categories (3,1) in monohybrid cross = 2 therefore degrees of freedom (n-1) = 1 9/4/13 P = 0.48 can be thought of as a 48% probability that similar variation would appear again due to chance. If p less than or equal to 0.05, reject null hypothesis Problems  # 18 and 19 (Chapter 3) How can you tell that this pedigree depicts an autosomal recessive trait?  Recessive traits typically skip generations.  Either 1-3 or 1-4 must be heterozygous.  2-1 and 2-2 are carriers.  Recessive autosomal traits appear equally in both sexes.  Questions: how would this pedigree be drawn to show an affected individual in generation III who died from Tay–sachs disease? Do affected individuals reproduce? Read Tay-sachs on p 48 How can you tell that this pedigree depicts an autosomal dominant trait?  Dominant traits almost always appear in each generation.  Affected individuals all have an affected parent.  Dominant autosomal traits appear equally in both sexes.  Anyone with an affected parent has a 50 % chance that they do inherit the affected allele.  1-1is heterozygous for a dominant allele.  Ie. Huntington‟s disease o Appears generally middle age after they have reproduced o Neurogenitive disorder  Affects muscle and other functions  Ie. Familial hypercholesterolemia o Affects LDL receptors o If heterozygous, you can have heart heart in 40s or younger o If homozygous, you can have heart attack before five and usually will before 20 Chapter 4: Modifications of Mendelian Inheritance Genetic linkage  An exception to independent assortment  Genes that occur on the same chromosome in close proximity will exhibit linkage. Alleles will be more likely to be inherited together than separate. X-Linked traits  Heterogametic sex (e.g. human males XY) only have one copy of X chromosome.  Early example: inheritance of white (w) in Drosophilia*.  Segregation ratios not the same as normal monohybrid cross o can be different than that of autosomal  Males are hemizygous (only have one copy of a gene): lack white locus on Y chromosome X- linked inheritance in flies  All daughters are red-eyed heterozygotes  All sons are white-eyed hemizygotes X-linked diseases  Also Duchenne muscular dystrophy, hemophilia  Color blindness is X–linked recessive X-linked dominant disease  Trait never passed from father to son  All daughters of an affected male are affected Wild-type = allele that occurs most frequently in a population Mutation is the source of new alleles. It can affect a characteristic of an organism because it can affect the function of an encoded protein. There can be multiple alleles for a particular gene (not just 2). More than 100 alleles of the white locus! Types of mutations  Loss-of-function: allele that results in reduction or elimination of the functional activity of the protein or RNA encoded by the affected gene (total elimination = null allele) o Ie. If protein was enzyme that bound to a substrate, the mutation affected the part of the protein that binds to the substrate to where it cannot bind  Gain-of-function: allele that results in increased expression or activity or ectopic (activity is present when it shouldn‟t be) activity of the affected gene product o Ie. Mutation can cause inappropriate expression and affect when protein is present during development (such as transcription factor) in different tissue or different times  Neutral: allele that does not detectably change the function of the gene affected o Ie. triplet changed still encodes same amino acid or new amino acid is similar enough to old amino acid that there is no real change in protein Incomplete/partial dominance  Snapdragons; neither R1 nor R2 allele is dominant  F2 ratio= 1 R1R1: 2 R1R2: 1 R2R2 9/6/13 Codominance  When 2 alleles of a single gene express distinct, detectable proteins  Ie. M and N forms of a gl
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