Study Guides (238,612)
Canada (115,252)
Biology (440)
Joe Kim (3)

REVIEW for Midterm 1 - Quicknotes - Bio 2C03

7 Pages
Unlock Document

McMaster University
Joe Kim

BIO 2C03 2013 Quicknotes Lecture 1 – Chapter 3+6 Sickle Cell Anemia  1904; Walter Noel had severe anemia; discovered by Dr. Ernest Irons and James Herrick  Symptoms – fatigue, pain crises, swelling and inflammation (RBC blocking own and WBC transport; bacterial infections not being combatted), bacterial infections (spleen enlarging and filling with dying RBC), splenic sequestration, lung and heart injury (cut off from oxygen), leg ulcers, cellular death  Anemia can be temporary due to disease of nutrition (eg/ low iron levels)  Haemoglobin – binds oxygen; enables transport of oxygen from lungs to target tissues by RBC; 90% of RBC proteins are haemoglobin o Tetramer; α2 2 each subunit associated with one heme (oxygen binding molecule) o Two genes determine structure - α-globin gene on chromosome 16, β-globin gene on chromosome 11 (3 exons, 2 introns, 1.6 kb) o HbA = normal gene; HbS = mutant, sickle cell  Common Cause – single nucleotide base pair substitution (SNP) in β-globin sequence; Glutamic Acid (charged) Valine (hydrophobic)  Sickle cells (haemoglobin aggregate into long polymer instead of tetramer) form with release of oxygen at capillaries; changes shape; rigid and inflexible; blocks flow of cells and interrupts delivery of oxygen to the tissues  Normal RBCs release oxygen as they pass through capillaries and maintain shape  RBC normal lifespan ~120 days; sickle cell lifespan ~10-20 days  RBC not replaced fast enough, results in anemia  Recessive Trait – need two alleles to appear  sickle cell anemia β β o James Neel, 1949 – examined parents of children with SDC; parents all heterozygous carries – thus, autosomal recessive allele S A A A o β β  carrier; β β  normal  Linus Pauling – characterize structure of haemoglobin o Gel Electrophoresis - β β two bands; β β one band; travels furthest (positive); β β one band travels least (negative)  Consistent with charge difference  Protein amount in band can be quantified using densitometry  Vernon Ingram o Fingerprint analysis of Haemoglobin  Treatment – aimed at avoiding crisis, relieving symptoms, preventing complications (blood transfusions, supplemental oxygen) o LT Solutions – bone marrow transplant, induce expression of fetal haemoglobin, gene therapy  Common among people whose ancestors come from sub-Saharan Africa, Spanish-speaking regions, Saudi Arabia, India and Mediterranean countries o Affects 72,000 in the US – mostly people from Africa (1/500 African American, 1/1000 Hispanic, 1/12 African Americans carry trait)  Levels of Analysis o Physiological - β allele is dominant o Cellular - β β two alleles both expressed; blood smear has both normal and sickled cells o Molecular - β β two alleles both expressed – both protein variants detected on gel  Environment affects phenotype o Normal Altitudes - β β individuals do not show symptoms of sickle cell anemia o Elevated Altitudes - β β individuals show phenotype of incomplete dominance; intermediate between two homozygous genotypes Mendel  Principle of Segregation – the two alleles of an allele pair segregate apart during gamete formation  Probability o Sum Rule – probability of several mutually exclusive events occurring; sum of individual events o Product Rule – probability of two independent events happening simultaneously; product of individual events  Mendelian Ratio (monohybrid) – 3:1 (phenotypic ratio)  Test Cross – used to reveal genotype; a cross between an organism of unknown genotype with a homozygous recessive individual for that trait Pedigrees  Modes of Inheritance 1. Autosomal Recessive Trait o 2 same recessive alleles o Equal frequency in males and females o “Skips generations” (heterozygous parents) o Mating between family increases likelihood of recessive trait 2. Autosomal Dominant Trait o Equal frequency in males and females o Does not “skip generations” (unless acquired by mutation) o If rare  people displaying trait are heterozygous 3. X-Linked Recessive Traits o More frequent in males (males only need to inherit 1 copy; females need to inherit 2 copies) o “skips generations” (eg/ unaffected mother  affected son) o not passed from father to son (passes Y chromosome) o affected father  carrier daughters 4. X-Linked Dominant Traits 1 BIO 2C03 2013 o More frequent in females (inherit X chromosome from mother and father) o Does not “skip generations” (must have affected parent to be affected) o Affected men  affected daughters (passes X chromosome); unaffected sons (passes Y chromosome) o Affected women  ½ affected daughters; ½ affected sons  If male is affected – received gene from mother 5. Y-Linked Traits o Only in males – passed father to son (all male offspring affected) o Does not “skip generations” of males Lecture 2 – Chapter 25  Mendelian Population – an interbreeding group that share the same “gene pool”  Evolution – changes in “gene pool”; changes in the frequencies of different alleles Malaria  Symptoms – headache, nausea, high fever, vomiting, flu-like symptoms, kidney and brain complications (lead to delirium and coma)  chronic; susceptible to other infections; can lead to death  Cause – protozoan (like Plasmodium falciparum); begins in larval development in mammalian host, transferred by a vector (mosquito) that carries protozoan  Plasmodium larvae mature in liver of host and later in RBCs  β mutation appears in high frequency in areas where malaria is presen(observati; β confers a selective advantag(hypothesis) o Individuals with β β and β β genotypes are more resistant to malaria than individuals with β β genotype – sickled cells are fragile and have shorter lifespan than normal RBCs  interrupts life cycle of Plasmodium larvae, preventing proliferation of malaria  Natural selection maintains both alleles – both homozygous phenotypes are maintained = balanced polymorphism S S S o β β – malaria resistant; sickle cell anemia causes death (often before reproduction)  loss of β o β β – die from malaria at high frequency  loss of β o β β – malaria resistant; no sickle cell anemia  gain β and β (heterozygote advantage)  Balanced Polymorphism = the loss of an allele in one genotype is balanced by a selective advantage in another genotEvidence: S o Overlay of maps of malaria incidence and higher frequency of β allele o Molecular evidence that β allele independently mutated and evolved to a high frequency four times in separate populations o Frequency of carriers increases with increasing age in a population  Inherited variation of α-globin and β-globin genes is most common cause of single gene disease in hum(World Health Organization) o ~250-300 million people are heterozygous carries o β allele o β allele – Position 26 Glu  Lys; less severe anemia; β β malaria resistant; variant found frequently in Asia and Pacific Island C C A o β allele – Position 6 Glu  Lys; less severe anemia; β β malaria resistant; mutation found primarily in West African populations  Linus Pauling – screening techniques to prevent sickle cell anemia o Heterozygous individuals should not marry each other or have children o Heterozygotes that are married to homozygous individuals that are not affected should have few children o Selection against β allele  taking sickle cell anemia in isolation, not considering β as advantageous  May 1, 2009; Georgia, USA – blood tests required before a marriage license is issued and sickle cell test recommended  Sickle Cell Anemia Screening  identify carriers and homozygous individuals; identify SNP in β-globin gene o Blood smears – identify individuals through the presence of sickled cells o Protein electrophoresis – identify variant Hb proteins o Can be done in utero; in the case of in vitro fertilization, can be associated with pre-implant genetic diagnosis (PGD) Genotypic and Allele Frequency  Genotypic frequency  find to calculate allele frequency; f (AA) + f (Aa) + f (aa) = 1 o f (AA) = number of AA individuals/total number of individuals  Allele frequency – the frequency of a single allele of a gene within the whole population (f (A) = p) o p = f (allele) = number of copies of the allele / number of copies of all alleles for that gene o p = f(A) = (2nAA+ nAa / 2n = (nAA + ½n Aa/ n = f (AA) + ½ f (Aa) o q = f(a) = (2naa n Aa/ 2n = (naa ½n )Aa n = f (aa) + ½ f (Aa) o p + q = 1 Hardy Weinberg Equilibrium  Gene Pool = total number of alleles of a gene in a population  p = f (A) = frequency of one allele; q = f (a) = frequency of alternate allele; o p+q=1 2 2  p = fraction of population homozygous, AA; q = fraction of population homozygous, aa; 2pq = fraction of population heterozygous, Aa o (p+q) = p + 2pq + q = 1  Hardy-Weinberg Principle – allele frequencies, gene frequencies and genotype ratios maintained; certain conditions must be met o Related to a single locus (eg/ no population is completely free of natural selection for all traits) o Population cannot evolve under HWE  HWE Conditions 1. No mutations – the composition of the gene pool remains the same generation after generation o Mutations – change the composition of the gene pool; new alleles introduced and allelic frequencies change 2. No gene flow (by migration) – isolation of a population prevent changes in gene pool by migration 2 BIO 2C03 2013 o Gene Flow by Migration – new alleles and alteration of gene frequency by introduction of individuals from different populations (distinct gene pools; alleles and allelic frequencies); adds variation to population; makes populations more similar to each other 3. No genetic drift – in large populations, loss of a few individuals has little effect on gene pool composition o Genetic Drift – different populations diverge; frequencies of populations change in different ways; occurs more often in small populations, where loss of individuals has significant effect on gene pool composition o Founder Effect – establishment of population by small number of individuals o Bottleneck Effect – populations undergoes drastic reduction in population size o Fixation – when an allele frequency reaches 0 or 1; leads to loss of diversity 4. No sexual selection (must be random mating) – gene frequencies change if individuals exhibit a preference in mate selection 5. No natural selection – if fitness isn’t a factor, then gene frequencies do not change because no allele has an advantage o Natural selection – differential reproductive success for different genotypes; if a genotype increases reproductive potential, the frequency of alleles for trait will increase Fitness  Fitness (W) – the relative reproductive success of one genotype compared to other genotypes within a population; natural selection requires that there are differences in fitness within a population o W = fitness = offspring of genotype/offspring of most successful genotype; S = selection coefficient = 1 – W o W bar= average population fitness = p WAA+ 2pqW +Bb W 2 bb  Can use these values to calculate new allele frequencies after one generation of selection  Summary BB Bb Bb Initial genotype frequency p2 q2 2pq Relative frequency W BB W Bb W bb Contribution of genotypes to population p W BB q W Bb 2pqW bb 2 2 Relative genotype frequency after selection p W BBW bar q W BbW bar 2pqW /bb bar (Contribution/average fitness)  Types of Natural Selection o In selection against both homozygotes, both alleles are favoured in heterozygotes – neither allele is eliminated from the population Fitness Relation Form of Selection Result W BBW > Bb bb Selection against recessive b B ; b W = W < W Selection against dominant B B ; b BB Bb bb W BBW > Bb bb Selection against incompletely dominant b B ; b W BBW < Bb bb Selection against incompletely dominant B B ; b W BBW > Bb bb Overdominance = heterozygote advantage Stable Equilibrium Sickle Cell Anemia W BBW < Bb bb Underdominance = heterozygous has lower fitness Unstable Equilibrium Lecture 3 – Chapter 3+5 Multiple Alleles  Polygenic – traits encoded by genes at many loci  Pleiotropic – many genes affect one trait  Multifactorial – traits polygenic and influenced by environment  Frameshift Mutation – loss of a single nucleotide causes the reading frame to be read differently; results in a non-functional protein; allele is a loss of function allele  Loss of Functional Allele – an enzyme or other protein is a) no longer being produced b) produced at lower levels c) nonfunctional  Wildtype Allele – functional enzyme or other protein is produced; most common phenol/geno  Haplosufficiency – wildtype allele is dominant over the loss of function allele; in heterozygote half as much protein is synthesized, but is sufficient to achieve normal phenotype (dominant allele is not always normal; eg/ cystic fibrosis)  Haploinsufficiency – dominant allele is loss of function allele; in heterozygote half of much protein is synthesized, which is not sufficient for normal phenotype (eg/tailless cats; manx)  Gain of function mutations in dominant alleles – dominant mutant allele produces a protein that has increased function o Can de detrimental  eg/ Huntington’s disease  Genotype Number of Multiple Alleles # of Alleles # of Genotypes Kinds of Homozygotes Kinds of Heterozygotes n n(n+1) / 2 n n (n-1) / 2  Eg/ Fur Coloration in Cats o Five alleles: C = full color c = Burmese c = Siamese c = white, blue eyes c = albino, pink eyes o C > c = c > c > c o Full Color Gene ,C – codes for Tyrosinase enzyme o Albino Gene, c – results from a cytosine deletion in tyrosinase at position 975, exon 2 = premature stop codon 9 residues downstream from the mutation (due to frameshift mutation) o Haplosufficiency – C/c genotype; half as much tyrosinase is produces, but is sufficient to achieve full coloration # of # of Kinds of Kinds of Alleles Genotypes Homozygotes Heterozygotes n = 5 n(n+1) / 2 n = 5 n (n-1) / 2 = = 15 10 3 BIO 2C03 2013 F2 Ratios – P gen = homozygous; F1 = heterozygous  F2  Law of Segregation – allele pairs separate or segregate during gamete formation and randomly unite at fertilization  Law of Independent Assortment – the inheritance pattern of one trait will not affect the inheritance pattern of another trait  Mendelian Ratio – Cross two heterozygotes for two independent traits (AaBbxAaBb)  9:3:3:1 phenotype offspring  Number of pheno/genotypic classes expected from self-crosses of heterozygotes (all genes show complete dominance) # Segregating # Phenotypic # Genotypic Gene Pairs Classes Classes n n n 2 3  Eg/ Trihybrid – cross of heterozygotes results; n = 3; phenotypes; phenotypes = 8; genotypes = 64; ratio = 27:9:9:9:3:3:3:1  Overview of Ratios Monohybrid 3:1 Complet
More Less

Related notes for BIOLOGY 2C03

Log In


Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.