Lecture Notes for General Biology BI 101 - Genetics
Nobel Prize Updates I Genetics - History A) Primitive civilizations - domestication of plants and animals, important demonstration of early genetic engineering, lead to agricultural development B) 1800's: 1)Mendel - laid down the foundation for the field of genetics C) early 1900's: 1) Morgan uses fruit flies, identifies chromosomes as region of cell where genes are stored in the cell 2) DeVries describes the first mutations in plants - rediscovers Mendel's work D) Modern Genetics - practical applications 1) Populations Genetics - Evolution 2) Oncology, oncogenes and Cancer 3) Genetic Disease and Gene Therapy 4) Recombinant Technology (e.g., crop resistance, animal breeding, etc...) 5) DNA Fingerprinting a) Human applications b) Wildlife Management and illegal importation of endangered species II Genetics - Mendelian Inheritance and beyond Mendel A) Definition 1) study of inheritance = transmission of traits from one generation to the next B) Mendel's experiments - experimental design 1) subject = pea plants 2) traits = flower color (purple, white), flower position (axial, terminal), seed color (yellow, green), seed shape (smooth, wrinkled), pod color (yellow, green), pod shape (inflated, constricted) 3) controlled breeding experiments a) paint brush and scissors (to remove stamens) = tools Stamen - male part of the plant that produces pollen Carpel - female part of the plant that produces eggs b) matings: pure x pure, like x unlike, offspring c) example - monohybrid cross C) Mendel's contributions 1) different morphological traits come in two's (e.g., smooth or wrinkled seed), must be 2 particles inside the cell that determine the morphological trait, alleles = alternative forms of a gene 2) always 2 particles in the adult (2N) = genes composed of 2 alleles 3) Relationships exists between alleles, most common is dominance 4) Law of segregation - alleles segregate on gametes 5) Law of independent assortment, two genes assort independently on the gametes 6) Modern terminology - Genes and Alleles a) two alleles = A (dominant), a (recessive) (A > a) b) three combinations of genes from two alleles = AA, Aa, aa AA = homozygote dominant aa = homozygote recessive Aa = heterozygote c) Phenotype = trait caused by the gene (two alleles) P = purple flower, p = white flower PP, Pp = purple flowers pp = purple flowers d) Punnett Square and making gametes 7) Mendel's experiments Results of various phenotypes and their corresponding genotypes Monohybrid cross - example of flower color (P - purple, p - white) 3 generations - P, F1, F2
Generation | Male | Female |
P | PP | pp |
Punnett Square for P | Female gametes | Female gametes |
Male gametes | p | p |
P | Pp | Pp |
P | Pp | Pp |
Results Offpsring of P | Males | Females |
Pp | Pp | |
Phenotypic Ratio | 100% Dominant, Purple flowers | |
Genotypic Ratio | 100% Pp | |
Generation | Male | Female | |
F1 | Pp | Pp | |
Punnett Square for P | Female gametes | Female gametes | |
Male gametes | P | p | |
P | PP | Pp | |
p | Pp | pp | |
F2 Generation | |||
Phenotypic Results - Offpsring of F1 | Purple flowers | White Flowers | |
Individuals | PP, Pp, Pp | pp | |
% | 3/4 = 75% | 1/4=25% | |
Phenotypic Ratio = 3:1 | 3 | 1 | |
Genotypic Results Offpsring of F1 | PP | Pp | pp |
PP | Pp, Pp | pp | |
1/4 | 2/4 | 1/4 | |
% | 25% | 50% | 25% |
Genotypic Ratio= 1:2:1 | 1 | 2 | 1 |
3 Types of Monohybrid crosses
Homozygous Dominant x Homozygous Dominant (similar results with recessive x recessive)AA x AA
Gametes A A A AA AA A AA AA Results Phenotypic Ratio 100% Dominant Genotypic Ratio 100% AA
Homozygous dominant x Heterozygote
AA x Aa
Gametes A a A AA Aa A AA Aa Results Phenotypic Ratio AA - dominant phenotype
AA - dominant phenotype
Aa - dominant phenotype
Aa - dominant phenotype
4 dominant phenotypes/4 offspring = 100%
100% Dominant
Genotypic Ratio 2 homozygous dominants (AA)/4 offspring = 50%
2 heterozygotes (Aa)/4 offspring = 50%
1 (AA):1 (Aa)
Homozygous recessive x Heterozygote
aa x Aa
Gametes A a a Aa aa a Aa aa Results Phenotypic Ratio Aa - dominant phenotype
Aa - dominant phenotype
aa - recessive phenotype
aa - recessive phenotype
2 dominant phenotypes/4 offspring = 50%
2 recessive phenotypes/4 offspring = 50%
1 dominant phenotype : 1 recessive phenotype
Genotypic Ratio 2 homozygous recessives (aa)/4 offspring = 50%
2 heterozygotes (Aa)/4 offspring = 50%
1 (aa):1 (Aa)
Heterozygote x Heterozygote
Aa x Aa
Gametes A a A AA Aa a Aa aa Results Phenotypic Ratio AA - dominant phenotype
Aa - dominant phenotype
Aa - dominant phenotype
aa - recessive phenotype
3 dominant phenotypes/4 offspring = 75%
1 recessive phenotype/4 offspring = 25%
3 (Dominant): 1 (recessive)
Genotypic Ratio 1 homozygous dominant (AA)/4 offspring = 25%
2 heterozygotes (Aa)/4 offspring = 50%
1 homozygous recessive (aa)/4 offspring = 25%
1 (AA) :2 (Aa):1 (aa)
Dihybrid cross - example
Generation | Y - yellow seed, y - green seed, R - round seed, r - wrinkled seed | ||||
P | YYRR x yyrr | ||||
F1 | YyRr x YyRr | ||||
F2 = ? | solution - break it up into two heterozygous crosses | ||||
Yy x Yy | Rr x Rr | ||||
Gametes | Y | y | Gametes | R | r |
Y | YY | Yy | R | RR | Rr |
y | Yy | yy | r | Rr | rr |
Results | |||||
Phenotypic Ratio for Monohybrid Crosses |
YY - dominant phenotype - yellow Yy - dominant phenotype - yellow Yy - dominant phenotype - yellow yy - recessive phenotype - green
3 dominant phenotypes (yellow)/4 offspring = 3/4 = 75% 1 recessive phenotype (green)/4 offspring = 1/4 = 25%
3 (Dominant) yellow: 1 (recessive) green |
RR - dominant phenotype - round Rr - dominant phenotype - round Rr - dominant phenotype - round rr - recessive phenotype - wrinkled
3 dominant phenotypes (round)/4 offspring = 3/4 = 75% 1 recessive phenotype (wrinkled)/4 offspring = 1/4 = 25%
3 (Dominant) round: 1 (recessive) wrinkled |
|||
Phenotypic Ratio for Dihybrid Crosses |
Possible Phenotypes (probability) |
Probabilities | |||
Yellow (3/4) round (3/4)
|
(3/4)(3/4)=9/16 | ||||
Yellow (3/4) wrinkled (1/4)
|
(3/4)(1/4)=3/16 | ||||
Green (1/4) round (3/4)
|
(1/4)(3/4)=3/16 | ||||
Green (1/4) wrinkled (1/4)
|
(1/4)(1/4)=1/16 |
E) Beyond Mendel
1) More than two alleles for a phenotype
a) Human blood groups - A, B, O
2) Relationships between genes -Epistasis
a) one gene masks the presence of another
b) hypothetical example of coat color B - black and dominant over b -brown C - color deposition and dominant over c - no color
Genotype | Phenotype |
BBCC | black coat |
BbCc | black coat |
bbCC | brown |
bbCc | brown |
Bbcc | brown (black turned off by cc) |
BBcc | brown (black turned off by cc) |
3) Expression of the phenotype is affected by the environment a) tanning, bleaching of hair, shaving, stunted trees near treeline 4) Codominance a) human blood groups (A, B, O) 5) Incomplete dominance a) snapdragons (Red x White = some red, some white, some pink plants) 6) Continuous variation and polygenic inheritance Distribution of data 7) Pleiotropy - one allele contributes information to 2 or more phenotypes III The Chromosomal Basis of Inheritance A) 3 Questions 1) Where are genes and alleles located? 2) How are they arranged? 3) How are they transmitted from one generation to the next? B) Search for genetic material - Genes on Chromosomes Morgan's study of Fruit Flies Eye color is sex-linked
Punnett SquareP Generation: X+X+ (pure wild) x XY (white eye males)
Gametes X Y X+ X+X X+Y X+ X+X X+Y Results Phenotypic Ratio 100% Dominant - wild/red-eye
F1 Generation X+X (wild heterozygote) x X+Y (wild males)
Gametes X+ Y X+ X+X+ X+Y X XX+ XY Results = F2 Generation Phenotypic Ratio X+X+, X+Y, XX+
3 wild/red-eye
XY
1 (white-eye) male
no white-eye females
C) Arrangement 1) Alleles are located on homologous chromosomes site of the allele is the locus D) Transmission of genes from generation to the next 1) Meiosis is the mechanisms, generates variation based on how the homologous chromosomes line up across from each other during Metaphase I 2) Other chromosome alterations occur during transmission a) inversions b) deletions c) crossing over E) Sex determination and Chromosomes
Organism | XX | XY | Other |
Human | female | male | |
Bird | male | female | |
Grasshopper | female | male X_ (no Y chromosome) | |
Bee |
diploid female haploid male |
F) Karyology - study of chromosome number process - karyotyping V Chemical Basis of Inheritance A) Makeup of Chromosomes Proteins - histones DNA coiling B) Genetics code in Proteins or DNA? 1) Griffiths Smooth and rough strains of bacteria 2) Hershey-Chase labeling radioisotopes and viruses 3) Watson and Crick (and Rosalind) describe double-helix Components of the Double Helix Nucleotide Phosphate, Sugar and Nitrogenous base Nitrogenous Bases Purines Adenine (A) and Guanine (G) Pyrimidines Cytosine (C) and Thymine (T) Bonds A bonds with T C bonds with G C) Arrangement of chemicals on the chromosome histones - proteins for DNA coiling non-coding DNA coding DNA introns and exons D) DNA replication semi-conservative model E) Making proteins/enzymes from information in DNA - Transcription and Translation Genes make proteins for biochemical reactions inside cell One gene one enzyme hypothesis Evidence - Garrod and alkaptonuria Evidence - Beadle and Tatum, neurospora mold Transcription in the nucleus extracting information with mRNA Translation at rough ER - uses codons from mRNA and anticodons from tRNA mRNA interacts with tRNA tRNA contains Amino Acids F) Transposons - jumping genes Barbara McLintock discovered them in corn VI Genetic Disease - Practical Applications A) Genetic diseases - occur at two levels 1) genic 2) chromosomes 3) Links to online resources on Genetic Disease Hereditary Disease Foundation Human Genetics: A Resource for Teachers Genetic Disorder Corner from the Genetic Science Learning Center at the University of Utah B) Diseases at the level of the gene (genic mutations) Recessive Disorders (homozygote recessive aa) 1) Hemophilia - blood clotting problems, victims bleed to death a) due to recessive allele - sex-linked 2) Sickle-cell anemia - lack proper blood proteins and RBC's are sickle shaped versus normal, unable to carry O2 efficiently, causes various symptoms a) due to recessive allele causes a simple substitution 3) Phenylketonuria - unable to produce enzymes to breakdown chemicals in diet soda, can lead to toxic buildup and death, check the warning on diet soda cans!! a) due to recessive allele 4) Galactosemia - unable to produce enzymes necessary for breakdown of galactose in milk, toxic buildup a) due to recessive allele b) Links to galactosemia web sites Galactosemia.com Information from the American Liver Foundation c) Galactosemia is not lactose intolerance (not a genetic disease, occurs over time and with aging) Information from NDDIC Information from NIH 5) Lesch-Nyhan disease - missing an enzyme necessary for purine metabolism, leads to hyperpuricemia, severe mental retardation, self-mutilation and renal failure X-linked recessive disease Dominant Disorders (homozygote dominant AA and heterozygote Aa) 6) Huntington's Disease - deterioration of nervous system a) due to dominant allele 7) Achondroplastic dwarfism - small stature, disproportionate limbs, short broad hands and feet, waddling gait a) due to dominant allele b) affects bone growth beginning at birth c) usually does not affect intelligence but psychological problems may occur when child realizes he/she is different 8) Familial hypercholesterolemia - causes severe elevation in total cholesterol and LDL, leads to high risk of CHD (coronary heart disease), problem occurs with malfunctioning LDL receptor proteins that affects LDL uptake 9) Mechanism - substitution of nitrogenous bases a) example: CAC mutates to CCC, A replaced by C, changes genetic information and results in production of ineffective proteins C) Syndromes and Chromosomal disorders Overview Extra chromosomes 1) Klinefelter's Syndrome - XXY sex chromosomes, sterile males, may show some female features 2) XYY Syndrome - extra Y in males a) individuals exhibit normal development and above average height,tendency to delayed mental maturation with an increased probability for learning problems 3) Metafemales - XXX, normal development and sexual characteristics, usually taller than other females with some learning difficulties 4) Down's Syndrome (Down Syndrome, Trisomy, Trisomy 21) - extra chromosome 21 , results in mental retardation, heart defects, more likely to occur in infants born to older women Missing chromosomes 5) Tuner's syndrome - X_, females lack one X chromosome, some mental retardation results in sterility, short in stature, never develop ovaries, increased incidence of thyroid problems 6) Mechanism a) Non-disjunction during meiosis, some gametes contain extra chromosome, other gametes are missing chromosome 7) Good link with summary of sex chromosome abnormalities D) Chromosomal rearrangements and Genetic Disease 1) Deletions a) Cri du Chat syndrome, broken chromosome results in retardation, malformed larynx and vocal problems b) Fragile X Syndrome - broken chromosome results in sterility mental retardation, oversized testes in males, double- jointedness E) Methods of Detection Pedigree analysis legend of terms actual pedigree Monitoring levels of chemicals in the blood CVS - chroionic villus sampling Amniocentesis V DNA Technology A) Recombinant Technology - genetic engineering 1) splicing genes from one organism into another organism B) Techniques 1) viral transfer - using viruses to transfer genes 2) restriction enzymes and plasmids in bacteria 3) gene gun and microprojectiles - small DNA coated pellets shot into the cell at high speed. 4) bacterial transformation and plants bacterial DNA plasmids bateria and transformation 5) Liposomes - small spheres with foreign DNA attach to and fuse with the cell membrane, DNA enters host cyptoplasm 6) Electroporation - host cell is shocked with small, rapid bursts of electrical currents which create gaps in the cell membrane and permit entry of foreign DNA 7) DNA injection with small micropipette (micromanipulator) used to inject DNA into host cell C) Why splice genes from one organisms into another - Treat Disease 1) Drugs and hormones produced by recombinant bacteria a) Using microbes to produce hormones or enzymes that individuals with genetic diseases can not make for themselves 1) Splice normal human genes into bacteria which will make the desired product, involves using restriction enzymes which cut the desired DNA sequence which is spliced on to bacteria chromosomes 2) examples - Human growth hormone, insulin, interferon, Factor VIII, vaccines 3) Summary table 4) Gene therapy/replacement a) defective genes are replaced with normal genes, works for some genetic diseases, in the experimental stages b) Cystic Fibrosis - defect in the CF transmembrane regulator (CFTR) gene that controls electrolyte (e.g., salts) transport in in the lung, pancreas, GI tract, current research on inhaling viruses with the genes to correct salt problem in lung cells, liposomes also used to transfer normal genes into cells c) SCID - WBC's are removed and cultured,infected with viruses containing normal genes, reintroduced back into the body d) Hemophilia - Greengard et al. (1997) reported success in dogs with hemophilia dogs missing clotting factor received new genes to produce clotting factor and were producing clotting factor 18 months later e) Familial hypercholesterolemia - working on LDL receptor protein, abnormal liver cells removed and exposed to viruses with genes for LDL recptor protein, new liver cells with gene from virus reintroduced into liver, LDL was lowered f) Gaucher's disease - inability to break down lipids that accumulate in the spleen, marrow, liver, and sometimes in the brain, high incidence in Ashkenazi Jews, autosomal recessive disorder, occurs in Macrophages (WBCs), stem cells are harvested and these cells receive new gene in cell culture from retroviruses, the new stem cells are put back into the patient where they go to the bone marrow and give rise to new macrophages with the new genes h) Application for treating cancer - suicide genes used to kill brain tumor cells, inject tumor cells in vivo with retrovirus containing suicide gene, then treat patient with acyclovir that kills cells D) Why splice genes from one organisms into another - Agriculture Various transgenic organisms: plants, mice, 1) Examples of transgenic plants with resistance to viruses a) Tomato, potato and tobacco 2) Examples of transgenic plants with resistance to insects a) cotton, corn 3) resistance to herbicides 4) retard spoilage in tomatoes 5) Supreme example - strawberry a) resistance to drought, salt tolerance, insects, viruses, cold and frost, taste VI Other Current Research in DNA Technology A) DNA analyses and Genetic Fingerprinting 1) DNA fingerprinting in the courtroom a) Comparison of variable fragment lengths (RFLP's), cut by restriction enzymes, comparisons are made by running electrophoretic gels stain DNA or proteins on the gels comparing the bands 2) PCR ability to make copies from small samples 3) DNA and Wildlife Management a) Protection of Endangered Wildlife and Poaching 1) Project to describe DNA of all big game species for comparison with suspicious meat from poachers or importers - genetic database 2) National Fish and Wildlife Forensics Laboratory 4) Identifying the remains of soldiers missing or killed in action a) Department of Defense web site B) DNA Sequencing - Human Genome Project Goals 1) Create a map of genes located on human chromosomes Examples - Chromosome viewer 2) identify all human genes (estimates from 30,000 - 100,000) ` 3) list the nucleotide sequence (A,T,C,G) for all human DNA 4) decsribe amount and degree of genetic variation among humans 5) consider and or illustrate ethical, legal, social issues concerning this information and how it should/can be used Current knowledge 1) We have about 30,000 - 40,000 genes 2) 95% of the DNA is non-coding DNA (repetitive sequences) 3) We share many genes with other organisms (from Yeast to Fruit Flies to Chimps) 4) Gene discovery - normal bodily functions, genetic diseases C) Cloning: Dolly a) First clones - tadpoles using embryonic cells and nuclear transfer b) Today - many organisms (sheep, cattle, mice, rabbits, pigs, goats, cats) using nuclear transfer and artifical twining c) Why clone 1) produce cloned animals to produce proteins to treat disease (milk in goats, sheep) 2) produce cloned and transgenic animals for organ transplantation 3) cloning extinct and endangered species Mouflon Lamb in Corsica and Sardinia 4) pet cloning 5) therapeutic human cloning and stem cells d) Cloning Webliography e) Overview of the process overview from the Roslin Institute endangered species model
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