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5/23/2017 1 Who is the GREATEST BIOLOGIST EVER? 5/23/2017 2 Why Gregor Mendel is the GREATEST BIOLOGIST EVER… Even though he wasn’t really a biologist 5/23/2017 3 Ch 14 Mendelian Genetics 5/23/2017 4 Pre-Mendel Predominate belief in “blending”, child is a mix of parents problem with this was traits skipping generations Terms early genetic study Character = detectable, inherited feature, ex. color Trait = variant of an inheritable character, ex. green or red color True-Breeding = always produce plants with same traits as parents, self fertilization Cross-Breeding = cross parents with different traits to create hybrids 5/23/2017 5 Generations are named P = parental F1= results of PxP F2= results of F1 x F1 5/23/2017 6 Mendel’s experiment Mendel looked at 7 characteristics, each had 1 alternate form that did not “blend” when cross-bred His experiment– if a cross of purple & white P’s gives all purple, then a cross between F1’s, self-pollinating, would produce white again in F2 generation results – 3:1 ratio of purple to white flowers, conclusions – ? 5/23/2017 7 Mendel’s experiment Mendel looked at 7 characteristics, each had 1 alternate form that did not “blend” when cross-bred His experiment– if a cross of purple & white P’s gives all purple, then a cross between F1’s, selfpollinating, would produce white again in F2 generation results – 3:1 ratio of purple to white flowers, conclusions Heritable trait for whiteness is masked Purple trait is dominant Extension 5/23/2017 If 2 purple P’s were mated, what ratio of traits would you expect to observe? 8 The ratio does not match the ideal. Create a plan to test if this difference is acceptable. 5/23/2017 9 So… there are alternate forms of the same gene = alleles, p265 we inherit one allele from each parent if alleles are different, one is dominant (noted by capital letter), one is recessive (lowercase letter) When do alleles segregate? 5/23/2017 10 So… there are alternate forms of the same gene = alleles, p265 we inherit one allele from each parent if alleles are different, one is dominant (noted by capital letter), one is recessive (lowercase letter) When do alleles segregate? Anaphase I 5/23/2017 11 More Terms homozygous – 2 identical alleles for a trait, ex. DD, dd heterozygous – 2 different alleles for a trait, carrier, ex. Dd phenotype – organism’s expressed traits, ex. color, height genotype – organism’s genetic makeup, letters, ex. PP, Pp 5/23/2017 12 Testcross – a cross between a recessive and an unknown tells if it is homo or heterozygous monohybrid cross – dealing with 1 trait dihybrid cross – 2 traits Trihybrid – 3 traits 5/23/2017 13 Mendel’s first postulate: Law of Segregation = allele pairs separate randomly during meiosis, p. 266 There are 2 alleles for flower color, if 1 purple and 1 white: there is a 50% chance of getting either allele Punnett square used to predict the results 5/23/2017 14 Mendel’s secondpostulate: Law of Independent Assortment when dealing with 2 or more traits, each allele of the different genes segregates independently of each other WHY? If cross 2 dihybrid heterozygotes, get 9:3:3:1 ratio 5/23/2017 15 Probability = mathematical chance of an event happening Rule of multiplication- probability of 2 events occurring at the same time = product of their individual probabilities 5/23/2017 Ex: 2 coins both coming up heads = ? Ex: If DdRr x DdRr what is probability of getting DDRR is ? 16 Probability = mathematical chance of an event happening Rule of multiplication- probability of 2 events occurring at the same time = product of their individual probabilities 5/23/2017 Ex. 2 coins both coming up heads = ½ x ½ = ¼ Ex: If DdRr x DdRr what is probability of getting DDRR is ? chance of DD = ¼, chance of RR = ¼ so ¼ x ¼ = 1/16 17 Rule of addition –p.270, probability that either of two or more mutually exclusive events will occur is calculated by adding the individual probabilities. What are the chances you will get heads or tails when you flip a coin? Ex. cross of 2 heterozygotes, what are chances of result being hetero? Use → trihybrid AaBbCc x AaBbCc ? chance of AabbCC? 5/23/2017 18 Rule of addition –p.270, probability that either of two or more mutually exclusive events will occur is calculated by adding the individual probabilities. What are the chances you will get heads or tails when you flip a coin? ½+½ =1 Ex. cross of 2 heterozygotes, what are chances of result being hetero? Chance of recessive egg + dominant sperm = ½ x ½ = ¼ Chance of dominant egg + recessive sperm = ½ x ½ = ¼ chance of hetero child is ¼ + ¼ = ½ Use → trihybrid AaBbCc x AaBbCc ? chance of AabbCC? 5/23/2017 19 Extensions: Mendel’s laws were not perfect, in fact, he was lucky (or wise) that he choose peas which have simple inheritance (except pod shape) Incomplete dominance = 1 allele is not completely dominant over the other thus, there is a 3rd phenotype, intermediate, ex.Carnations/snapdragons p. 271 5/23/2017 20 Codominance = both alleles are expressed Level of expression varies at different levels ex: Tay-sachs 5/23/2017 at the molecular level – looks codominant – both alleles transcribed at the biochemical level – looks like incomplete→ a partial level of lipid-metabolizing activity at the organismal level – heterozygotes are symptom free, homoygote recessives express disorder 21 Multiple Alleles = genes that have more than 2 alleles Ex. blood groups A, B, AB, O (surface carbohydrates) blood type is the antigen present on the RBC, p. 273 also contains Rh factor, + or – with standard Mendelian rules 5/23/2017 22 5/23/2017 23 Pleiotropy = a single gene has multiple effects ex: sickle-cell 5/23/2017 24 Epistasis = one gene affects the expression of another gene, Ex. pigments in mice 5/23/2017 25 Polygenic inheritance = many genes affect the same trait Ex: skin color, very dark to very light, p. 274 5/23/2017 26 Environment plays an important part in gene expression, how much is dependent on the gene, nature vs. nurture argument Norm of Reaction = The phenotypic range for a genotype, p.275 5/23/2017 27 Humans Pedigree – family tree that shows inheritance over many generations, shows patterns = male, O = female, ●= affected, ○= non-affected 5/23/2017 28 Recessive human disorders - usually caused by a defective protein - heterozygotes are carriers Why more common than dominant disorders? Examples Cystic Fibrosis – most common amongst Europeans (4% carry), membrane protein that controls Cl⁻ traffic, causes increase mucus in lungs infections persist Tay-Sachs – higher in Ashkenazic Jews, can’t break down a type of lipid. How can it be high in a particular pop? Sickle cell – substitution in one hemoglobin, causes RBC to sickle and clog, carriers are immune to malaria, p. 278 In which pop. would sickle cell predominate? Consanguinity – mating with relatives, increases expression of recessive disorders. Why? 5/23/2017 29 Dominant inherited disorders – rarer than recessive. Why? Examples Achondroplasia – type of dwarfism Huntington's – late acting degeneration of nervous system, due to single allele on tip of chromosme #4 Knowledge of this makes disease detectable. Multifactorial disorders many different factors affect onset, but genetic predisposure present ex. Heart disease, diabetes, cancer 5/23/2017 30 Genetic testing and counseling 1) carrier recognition - help make decisions about whether or not to reproduce 2) fetal tests Can test for Tay-Sachs, sickle-cell, and cystic fibrosis, etc. amniocentesis – take amniotic fluid from around fetus, do karyotype chorionic villus sampling (CVS) – take villi, do karyoptype, fast, earlier, more risk, p. 280 ultrasound – imagery using sound waves, look for physical problems fetoscopy – fiber optics Culturing escaped fetal blood cells in mother’s blood 3) Newborn screening – ex. PKU 5/23/2017 31 5/23/2017 32 Big Picture of Inheritance… must be looked in integrated light…i.e. it is a product of genes working collectively and is influenced by environmental cues Must view emergent properties of organism as a whole, not a reductionist view of single genes acting in isolation So, why is Gregor Mendel the GREATEST BIOLOGIST EVER? Even though he wasn’t really a biologist 5/23/2017 34 Ch 15 Chromosomes and Inheritance 5/23/2017 35 Chromosome theory of inheritance: genes are located on chromosomes, they segregate and independently assort 5/23/2017 36 T.H.Morgan rediscovered Mendel’s work 1900’s, specific genes on specific chromosomes? work on fruit fly, why? fast repro., easy to handle, 4 pairs of chromosomes (1 pair are sex chromosomes) gene symbol is based on the mutant or recessive ex. curly is recessive = Cy, if normal then Cy+ wild type is the type seen in nature = + 5/23/2017 37 Experiment- p 289 white eyed male (♂)→ crossed with a red eyed female (♀)→ in F2 only males had white eyes ? how is no independent assortment possible? 5/23/2017 38 Experiment- p 289 white eyed male (♂)→ crossed with a red eyed female (♀)→ in F2 only males had white eyes ? → eye color and sex are linked Linked genes = when genes are on the same chromosome, so they are inherited together 5/23/2017 39 Sex linked traits = located on a sex chromosome, p. 290, ex. Hemophilia few genes on the Y, thus most sex-linked diseases are seen in males b/c on the X (not masked), females often carriers, p. 290 X-inactivation = females inactivate one of their X’s (see cat diagram) inactive X becomes a Barr body Typically both chromosomes’ genes are expressed 5/23/2017 40 Examining 2 genes: How could you determine if a two genes were “linked”? How could you tell distance between two genes? 41 Examining 2 genes: How could you determine if a two genes were “linked”? How could you tell distance between two genes? 5/23/2017 42 Recombination = offspring with different combinations of traits than the parents, caused by crossing over or mutations Parental types – same phenotype as a parent Recombinants – differ from parents, *p. 293-294 5/23/2017 What is % of recombination of the peas? 43 Recombination = offspring with different combinations of traits than the parents, caused by crossing over or mutations Parental types – same phenotype as a parent Recombinants – differ from parents, *p. 293-294 What is % of recombination of the peas? 50% - one-half of the offspring are expected to inherit either of the two phenotypes 5/23/2017 44 Recombination What would a recombination of 25% tell you about the chromosomal location of two given genes? 5/23/2017 45 Recombination What would a recombination of 25% tell you about the chromosomal location of two given genes? The genes’ loci are on the same chromosome Why is the recombination % not 0? What would a recombination of 0.5% tell you about their respective locations? 5/23/2017 46 Recombination What would a recombination of 25% tell you about the chromosomal location of two given genes? The genes’ loci are on the same chromosome Why is the recombination % not 0? Crossing-over separates them What would a recombination of 0.5% tell you about their respective locations? 5/23/2017 That their respective loci are in close proximity on the same chromosome 47 Sturtevant and gene mapping use recombination frequency to determine distance of genes The farther apart two genes are, the higher the probability that crossover will occur between them and ∴ the higher the recombination frequency made chromosome maps find relative distance between farthest genes, find distance of an end and a middle, fill in other genes double crossovers can occur too, throw # off a little Made distance unit: 1 map unit = 1% recombination 5/23/2017 48 5/23/2017 49 Final product: a genetic (linkage) map 5/23/2017 50 HUMAN GENETIC DISORDERS 5/23/2017 51 Nondisjunction –two chromosomes stuck together or not present Why and when would this occur? 5/23/2017 52 Nondisjunction –two chromosomes stuck together or not present Why and when would this occur? Aneuploidy = having an abnormal # of chromosomes Trisomy – 3 copies of 1 chromosome Monosomy – 1 copy of the chromosome Polyploidy = more than normal chromosome set Triploidy – 3 chromosome sets (3N) 5/23/2017 53 Nondisjunction –two chromosomes stuck together or not present Why and when would this occur? Aneuploidy = having an abnormal # of chromosomes Trisomy – 3 copies of 1 chromosome Monosomy – 1 copy of the chromosome Polyploidy = more than normal chromosome set Triploidy – 3 chromosome sets (3N) 5/23/2017 54 Basic Mutations Deletion – chromosome loses a piece, p. 298 Duplication – double of gene Inversion – chromosome is in reverse Translocation – gene moves to another chromosome →caused by UV light, chemicals or random →effects can be silent, lethal or in between 5/23/2017 55 Human aneuploid conditions Down Syndrome – trisomy 21, female age makes more frequent? Klinefelters – XXY, XXXY male, sterile, some female features XYY – male, usually normal, XXX- female, usually normal Turner syndrome – X, female, sterile, few sexual features Some effects of chromosomal abnormalities depend on what parent inherited by (genomic imprinting, p.300) - Prader–Willi disorder– deletion of part of #15 from dad - Angelman syndrome– deletion of same part of # 15 from mom, motor issues 5/23/2017 56 Genomic Imprinting is the activation or deactivation of a gene depending upon whether it was inherited from mom or dad Mechanism is typically methylation (adding of methyl group, –CH3 ). Methyl group acts as an on/off switch. 5/23/2017 Key player in epigenetics 57 Organelles and their genes Do not follow Mendelian rules of inheritance. 5/23/2017 Why? 58 Organelles and their genes Do not follow Mendelian rules of inheritance. 5/23/2017 Why? They do not undergo meiosis 59 Study tip of the day: always be able to explain text chapter concepts Concept 15.1: Mendelian inheritance has its physical basis in the behavior of chromosomes Concept 15.2: Sex-linked genes exhibit unique patterns of inheritance Concept 15.3: Linked genes tend to be inherited together because they are located near each other on the same chromosome Concept 15.4: Alterations of chromosome number or structure cause some genetic disorders Concept 15.5: Some inheritance patterns are exceptions to standard Mendelian inheritance 5/23/2017 60 Chapter 14 & 15 Quiz pedigree charts 5/23/2017 62 Pedigree Practice Problems: Identify each pedigree autosomal recessive, autosomal dominant, X-linked, or Y-linked 5/23/2017 as 63 Pedigree Practice Problems: Identify each pedigree autosomal recessive, autosomal dominant, X-linked, or Y-linked as ANSWERS a. autosomal recessive b. autosomal dominant 5/23/2017 64 5/23/2017 65 ANSWERS c. autosomal dominant d. autosomal recessive e. x-linked recessive 5/23/2017 66 5/23/2017 67 ANSWERS f. autosomal dominant g. autosomal recessive 5/23/2017 68 Chapter 14 1. 2. If a plant with purple flowers produces only the same variety as the parent plant over many generations, what is the plant said to be? What is Mendel’s law that states that the two alleles for a heritable character separate from each other during gamete formation? Chapter 14 1. 2. True-breeding plants Law of Segregation 3. If two heterozygous purple flowers produce offspring, what are the odds that the offspring will have white flowers? 4. The child’s mother has blonde hair, and their father is heterozygous and has brown hair. If blonde hair is a recessive trait, what are the odds that the child would have blonde hair? 5. When red snapdragons are crossed with white snapdragons their offspring is pink. What type of dominance is this? 5/23/2017 71 3. 25% 4. 50% 5. Incomplete 5/23/2017 72 Chapter 15 1. The law that states that alleles of genes on nonhomologous chromosomes assort independently during gamete formation is? 2. Who has a greater chance to receive Xlinked recessive disorders? Males or females? 3. Genes located near each other on the same chromosome tend to be inherited together in genetic crosses are called ? Chapter 15 1. Law of Independent Assortment 2. Males 3. Linked Genes 4. When the members of a pair of homologous chromosomes do not move apart properly during meiosis I they can alter the chromosome structure. What is this error called? 5. What are the four types of changes that can occur to chromosome structure? 5/23/2017 75 4. Nondisjunction 5. Deletion, duplication, inversion, translocation 5/23/2017 76 Try your luck at… practice pedigree problems Or more on following pages 5/23/2017 77 Dominant or recessive? autosomal, x-, or y-linked? 5/23/2017 78 5/23/2017 79 5/23/2017 80 A 5/23/2017 81 5/23/2017 82