HLTH 103 Biological Determinants of Health Genes & Genetics PDF

HLTH 103 – Biological Determinants of Health Genes & Genetics Health Sciences PART B Genes & Genetics  PART A:  Case Study: Sickle Cell Anemia & Malaria  Part B:  Gregor Mendel & Mendelian Genetics  Patterns of Inheritance Beyond Mendel  Part C:  Genes, Genetics, and Ge...

HLTH 103 – Biological Determinants of Health Genes & Genetics Health Sciences PART B Genes & Genetics  PART A:  Case Study: Sickle Cell Anemia & Malaria  Part B:  Gregor Mendel & Mendelian Genetics  Patterns of Inheritance Beyond Mendel  Part C:  Genes, Genetics, and Genomics  Nucleic Acids (Cellular Building Blocks)  Processing of Genetic Content Adapted From: Bozzone, Biology for the Informed Citizen, © 2014 by Oxford University Press Gregor Mendel Gregor Mendel, 1822-1884 Considered the father of genetics Entered monastery and became a priest He was interested in patterns of inheritance and began some experiments at the monastery where he resided in Austria Conducted historic experiments with pea plants Pea plants were ideal due to there multiple characteristics that could be clearly and easily observed His paper was ignored at the time, but his findings were independently rediscovered years later Adapted From: Bozzone, Biology for the Informed Citizen, © 2014 by Oxford University Press Gregor Mendel: Pea Plant (Pisum sativum)  Pea Plants have several advantageous properties making them ideal to use in these studies:  Several different and variable TRAITS that  self-fertilizing: Female gamete fertilized by male Stamen Stigma gamete from same plant  Easy to breed true-breeding lines (exhibit the same trait)  Large flowers make crosses easy when desired  Cross-fertilization or hybridization Ovule Ovary Adapted From: Bozzone, Biology for the Informed Citizen, © 2014 by Oxford University Press Gregor Mendel: TRAITS of Pea Plants  Seed Shape: round vs wrinkled  See Color: yellow vs green  Flower Color: purple vs white  Pod Shape: smooth (inflated) vs constricted  Pod Color: yellow vs green  Flower Pattern: axial vs terminal  Stem Height: tall vs short (dwarf) Source: Adapted From: Bozzone, Biology for the Informed Citizen, © 2014 by Oxford University Press https://opentextbc.ca/biology/wp-content/uploads/sites/96/2015/02/Figure_08_01_03.jpgcal Gregor Mendel: Cross Fertilization of Pea Plants Stamens Stigma 1Remove stamens 2Transfer pollen from from purple flower. stamens of white flower to the stigma of a purple flower. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Adapted From: Bozzone, Biology for the Informed Citizen, © 2014 by Oxford University Press Patterns of Genetic Inheritance: Gregor Mendel’s Experiments Experimental Results & Patterns of Inheritance 1. Mendel focused on one trait at a time. 2. Mendel followed the cross for more than one generation. 3. Mendel collected quantitative data and kept detailed records. 4. Mendel’s research revealed some basic rules of inheritance.  Genes can come in more than one form, or allele.  Alleles of a particular gene sort individually into gametes during meiosis.  Certain traits are dominant, while others are recessive.  The dominant trait is the one that is seen even when only one allele is present.  The recessive trait is the one that is not seen when only one allele is present. Adapted From: Bozzone, Biology for the Informed Citizen, © 2014 by Oxford University Press Patterns of Genetic Inheritance  Punnett square analysis  used to predict patterns of inheritance  alleles will be indicated as upper and lower case letters  In a Punnett square:  the possible alleles of one parent are placed on one axis Example: In a Punnett square, the possible combinations of male and female gametes  the possible alleles of the other parent are placed are placed on two axes, and then the possible combinations of the offspring are plotted in on the other axis the enclosed squares. This square shows that in a cross between two hetero-zygotes only  possible combinations of parental alleles are half the offspring will be heterozygotes. written in the squares within the grid Adapted From: Bozzone, Biology for the Informed Citizen, © 2014 by Oxford University Press  P Patterns of Genetic Inheritance generatio n PP X pp purple X Experimental Results & Patterns of Inheritance white P-generation: true-pure breeding parents Sperm from P-Parent (pp) homozygous dominant X homozygous recessive F1 plant generatio mating results in F1-generation n Eggs Pp Pp from P- Parent Pp Results: all F1-generation: offspring of P-mating cross (PP) Pp (purple) plant Pp all heterozygous dominant Pp mating results in F2-generation Sperm from F1 (Pp) plant F2 generatio F2 generation: offspring of F1-cross-fertilization n Results: (heterozygous dominant X heterozygous dominant)Eggs 1: PP from F1 results: 1: 2: 1 genotype; 3: 1 phenotype (Pp) (purple) plant 2: Pp recessive Adapted From: Bozzone, trait Biology for the re-appears Informed Citizen, © 2014 by Oxford University Press (purple) Testcross  Cross the unknown individual to a homozygous recessive individual  If some offspring display the recessive phenotype, unknown individual must have been heterozygous dominant  If all offspring display the dominant phenotype, unknown individual was homozygous dominant Adapted From: Bozzone, Biology for the Informed Citizen, © 2014 by Oxford University Press Patterns of Genetic Inheritance: Punnett Squares Adapted From: Bozzone, Biology for the Informed Citizen, © 2014 by Oxford University Press  KEY: Patterns of Genetic Inheritance Y = yellow peas y = green P Generation F1 Generation peas Cross cross Yellow pea Yellow pea YY Yy Green pea Yellow pea yy Yy Adapted From: Bozzone, Biology for the Informed Citizen, © 2014 by Oxford University Press Patterns of Genetic Inheritance Sperm (Father) gametes Bb ♂ B b ♀ BB Bb B Summary of Offspring/Progeny: Eggs 50% = Bb = Heterozygous Gametes Bb Bb bb Dominant b 25% = BB = Homozygous Dominant 25% = bb = Homozygous Adapted From: Bozzone, Biology for the Informed Citizen, © 2014 by Oxford University Press Patterns of Genetic Inheritance: Punnett Square Practice Sperm (Father) gametes _____ ♂ ♀ Egg (Mother) Gametes ____ Adapted From: Bozzone, Biology for the Informed Citizen, © 2014 by Oxford University Press Patterns of Genetic Inheritance: Mendel’s Results Characteris Contrasting P0 F1 Offspri F2 Offspring F2 Trait tic Traits ng Traits Traits Ratios 100% Flower color Violet vs. white 705 violet: 224 white 3.15:1 violet Flower Axial vs. terminal 100% axial 651 axial: 207 terminal 3.14:1 position Plant height Tall vs. dwarf 100% tall 787 tall: 277 dwarf 2.84:1 100% 5,474 round: 1,850 Seed texture Round vs. wrinkled 2.96:1 round wrinkled 100% 6,022 yellow: 2,001 Seed color Yellow vs. green 3.01:1 yellow green Pea pod Inflated vs. 100% 882 inflated: 299 2.95:1 texture constricted inflated constricted Pea pod 100% Green vs. yellow 428 green: 152 yellow 2.82:1 color green Adapted From: Bozzone, Biology for the Informed Citizen, © 2014 by Oxford University Press Patterns of Genetic Inheritance: Mendel’s Laws Mendel’s Law of Segregation The two copies of each gene segregate, or separate, during gamete formation and end up in different gametes. Adapted From: Bozzone, Biology for the Informed Citizen, © 2014 by Oxford University Press Patterns of Genetic Inheritance: Mendel’s Laws Law of Independent Assortment Alleles of different genes assort independently of each other during gamete formation (meiosis). Adapted From: Bozzone, Biology for the Informed Citizen, © 2014 by Oxford University Press Patterns of Genetic Inheritance: Mendel’s Laws Mendel developed two “laws” of inheritance based on analysis of his experimental data  Law of segregation: two alleles of each gene separate during gamete formation and end up in different gametes  Law of independent assortment: genes for different traits are separated from each other independently during meiosis (applies in most cases)  Certain traits are dominant, while others are recessive.  Dominant allele  The dominant trait is the one that is seen even when only one allele is present.  Masks or suppresses the expression of its complementary allele  Always expressed, even if heterozygous  Recessive allele  Will not be expressed if paired with a dominant allele (heterozygous)  Will only be expressed if individual is homozygous for the recessive allele  The recessive trait is the one that is not seen (masked) when only one allele is present. Adapted From: Bozzone, Biology for the Informed Citizen, © 2014 by Oxford University Press Patterns of Genetic Inheritance: Dominant Alleles  Dominant refers to how the allele behaves in combination with a recessive allele in a heterozygote  Dominant does not refer to the frequency of the allele in the population or to whether the allele encodes a “normal” phenotype  Some dominant alleles encode an abnormal or disease phenotype while the recessive counterparts encode the normal phenotype  Polydactyly (extra finger/toe): dominant allele (P) ▪ The vast majority of people are pp (homozygous recessive) with five digits on each hand/foot  Achondroplasia (dwarfism): Presence of one Adapted From: Bozzone, Biology for the Informed Citizen, © 2014 by Oxford University Press Patterns of Genetic Inheritance: Freckles Examples of Traits Influenced by Dominant and Recessive Alleles  Freckles: determined by the MC1R gene  Dominant allele (F): produces freckles  Recessive allele (f): no freckles  Genotypes FF and Ff will have freckles  Genotype ff will not have freckles Adapted From: Bozzone, Biology for the Informed Citizen, © 2014 by Oxford University Press Patterns of Genetic Inheritance: PTC (phenylthiocarbamide) Examples of Traits Influenced by Dominant and Recessive Alleles  Taster: gene determines ability to taste the chemical PTC (phenylthiocarbamide)  Dominant allele (T): taster, PTC is bitter  Recessive allele (t): non-taster, can’t taste PTC  Genotypes TT and Tt: can taste PTC, bitter sensation  Genotype tt: non-taster phenotype Adapted From: Bozzone, Biology for the Informed Citizen, © 2014 by Oxford University Press Patterns of Genetic Inheritance: Cystic Fibrosis (CFTR)  Cystic fibrosis: results from inheriting a recessive allele of the CFTR gene from each parent  CFTR (cystic fibrosis transmembrane conductance regulator gene): encodes a protein that transports chloride across the plasma membrane  Individuals with two copies of the defective recessive allele (homozygous recessive): functional CFTR protein is not produced ▪ Impaired chloride transport—very thick mucus accumulates in the lungs ▪ Interferes with breathing, frequent pulmonary infections  Heterozygotes (have one normal allele and one defective allele) produce the transport protein and have a normal phenotype Adapted From: Bozzone, Biology for the Informed Citizen, © 2014 by Oxford University Press Two-Trait Crosses: Independent Assortment of Genes for Different Traits  Outcome of two-trait crosses can be predicted by Punnett square analysis  Law of independent assortment  The alleles of different genes are distributed to gametes independently during meiosis  This law applies only if the two genes in question are on different chromosomes  Example of a two-trait cross:  Cross FFTT (homozygous freckles/taster) with fftt (no freckles, non taster)  All offspring are FfTt (heterozygous for both alleles)  Next, cross FfTt with FfTt Adapted From: Bozzone, Biology for the Informed Citizen, © 2014 by Oxford University Press Two-Trait Crosses: Freckles and PTC Independent Assortment of Alleles for Different Traits Adapted From: Bozzone, Biology for the Informed Citizen, © 2014 by Oxford University Press Two-Trait Crosses: Eggs Sperm Adapted From: Bozzone, Biology for the Informed Citizen, © 2014 by Oxford University Press Patterns of Inheritance beyond Mendel  Mendel’s rules do not completely explain inheritance  Inheritance can be much more complicated:  Alleles can interact, so can genes  Genes do not always affect just one characteristic  Gene expression depends on the environment  Example: Flowers of Hydrangea will vary depending on the acidity of the soil  Example: Carp are a slender fish if they develop in the absence of predators. If they are present, body shape changes. Adapted From: Bozzone, Biology for the Informed Citizen, © 2014 by Oxford University Press Patterns of Inheritance beyond Mendel  Complete Dominance (1 genotype; 1 phenotype)  Incomplete Dominance (both genotypes; blended phenotype)  Co-dominance (both genotypes; both phenotype both)  Sex-linked inheritance Examples:  Red-green color deficiency  Hemophilia A & Hemophilia B  Duchenne Muscular Dystrophy Adapted From: Bozzone, Biology for the Informed Citizen, © 2014 by Oxford University Press Patterns of Inheritance beyond Mendel: CO- DOMINANCE CO-DOMINANCE: Human Blood Groups  Codominance: heterozygotes express both inherited alleles equally  Example: Genes for ABO blood types ▪ A-allele and B-allele are co-dominant An individual heterozygous for the A and B alleles will be blood type AB, expressing both A and B antigens on red blood cells Adapted From: Bozzone, Biology for the Informed Citizen, © 2014 by Oxford University Press  Patterns of Inheritance beyond Mendel CO-DOMINANCE: Human Blood Groups  Codominance: heterozygotes express both inherited alleles equally  Example: AB blood type: A-allele and B-allele are co-dominant  an individual heterozygous for the A and B alleles will be blood type AB, expressing both A and B antigens on red blood cells Type O Type A Type B Type AB Antigen A Antigen B Antigen A Antigen B RBC RBC RBC RBC N-Acetyl- Galactose galactosamine Blood type: O A B AB Genotype: ii IAIA or IAi IBIB or IBi IA IB Surface antigen: Neither A nor B A B A and B Antibodies: anti-A and anti-B Anti-B Anti-A None Percentage: 45% 40% 10% 5% Adapted From: Bozzone, Biology for the Informed Citizen, © 2014 by Oxford University Press Patterns of Inheritance beyond Mendel: Biological SEX Sex Determination:  Sex determined by X & Y-chromosomes  XX = female; XY = male  Y-chromosome = 78 genes  X-chromosome = 900-1200 genes  X & Y chromosomes:  homologous portions  non-homologous portions  Y-chromosome non-homologous portion contain holandric traits Adapted From: Bozzone, Biology for the Informed Citizen, © 2014 by Oxford University Press  Patterns of Inheritance beyond Mendel: Biological SEX Female Sex-linked inheritance  Sex-linked genes are located on sex chromosomes Carrier  Recessive traits - X-linked inheritance Examples: Male  Red-green color blindness Normal femaleCarrier female  Hemophilia A & Hemophilia B Normal  Duchenne muscular dystrophy Hemophil Normal male iac male Adapted From: Bozzone, Biology for the Informed Citizen, © 2014 by Oxford University Press Patterns of Inheritance beyond Mendel: Biological SEX © OpenStax Biology Adapted From: Bozzone, Biology for the Informed Citizen, © 2014 by Oxford University Press Polygenic Inheritance: Phenotype Is Influenced by Many Genes  Inheritance of phenotypic traits that depend on many genes is called polygenic inheritance  Examples of polygenic traits:  Eye color, skin color  Height, body size, and body shape  Polygenic traits are usually distributed within a population as a continuous range of values Adapted From: Bozzone, Biology for the Informed Citizen, © 2014 by Oxford University Press Both Genotype and the Environment Affect Phenotype  Phenotype isn’t determined by genotype alone  Environmental factors can profoundly influence phenotype  Example: ▪ Nutrition affects height, body size  Genes carry instructions for making proteins, but environment influences how genes are expressed and how they contribute to one’s phenotype  Environment may produce epigenetic changes in D N A Adapted From: Bozzone, Biology for the Informed Citizen, © 2014 by Oxford University Press What Is Epigenetic Inheritance?  Refers to the modification and transmission of traits in ways that do not directly involve changes in the nucleotide sequence of a gene  Environmental factors can modify D N A without changing the sequence  Addition of methyl groups  These changes affect the frequency with which these modified genes are expressed, and in what cells they are expressed  Different methylation patterns explain why identical twins become more different as they age Adapted From: Bozzone, Biology for the Informed Citizen, © 2014 by Oxford University Press Adapted From: Bozzone, Biology for the Informed Citizen, © 2014 by Oxford University Press