III. Genetics & Genetic Engineering Presentation # 3 Ch. 11, 13, & 14 • Gregor Mendel - the ―Father of Genetics‖ • Was an Austrian monk • Worked in a monastery garden • Cross-pollinated plants, studied traits (characteristics) of offspring • Looked at true-breeding pea plants - if pollinated produced offspring identical to themself • Looked at hybrids - the offspring of crosses between parents of different traits
Some of Mendel’s crosses: Section 11-1 Seed Seed Seed Coat Pod Pod Flower Plant Shape Color Color Shape Color Position Height Round Yellow Gray Smooth Green Axial TallWrinkled Green White Constricted Yellow Terminal ShortRound Yellow Gray Smooth Green Axial Tall
III. Genetics– A . Terms to Memorize: • 1. Gene - units of DNA passed from parent to offspring. Each adult has two copies of each gene - 1 from each parent • 2. Allele - a specific form or expression of a gene trait – Example - brown eyes, Curly hair. • 3. Dominant - an allele that is always expressed or seen – Dark pigments are usually dominant • 4. Recessive - an allele that is can be hidden, it will not be expressed if present with a dominant allele • 5. Phenotype - actual gene expression - what is physically seen • 6. Genotype - the actual pair of alleles present – Homozygous = same 2 alleles in gene pair BB, bb (purebred) – Heterozygous= = different alleles present in gene pair Bb, Tt (Hybrid) • 7. Probability - the likelihood that a particular event will occur - Q:If you flip a coin 4 times in a row, what is the probability that it will land on tails every time? - A: 1/2 x 1//2 x 1/2 x 1/2 = 1/16 Each coin flip is an independent event. - Q: What is the probability of having 3 girls in a row?
III. GeneticsProbability can help us predict the outcomes of genetic crosses. – B. Genetic Crosses • 1. Monohybrid - 1 trait crosses – Studies 1 set of alleles from both parents – a) identify the trait and letters to be used - brown hair (B) or blond (b) – b) write the genotypes - i.e. Bb or BB or bb for both parents – c) separate the alleles into possible gametes b , B for each parent – d) draw a Punnett square and write one allele by each row and column – Join gametes together – Determine ratios of phenotypes and genotypes B B B b
III. Genetics– B. Genetic Crosses • 2.Dihybrid - 2 trait crosses – Studies 2 sets of alleles from both parents – Steps are the same but more complex because of more combinations – To identify # of possible gametes - look at how many different alleles there are for each trait then multiply. – Example - BbFf - 2 different b’s and 2 different f’s 2x2=4 – Use foil to get possible gametes f-firsts, 0-outer, i-inner, l-lasts – Use punnett square to determine offspring
III. Genetics– B. Genetic Crosses • 3. Incomplete Dominance – Two alleles are neither dominant or recessive – The two show a blending of their phenotypes – Example: red carnations crossed with white carnations produce all pink carnations – CRCR= red CW CW = white CRCW = pink • 4. Co dominance – Two alleles are both dominant or expressed at the same time – Example: hair color in cattle Red and White hair crossed = Roan – HRHR = red hair HWHW = white HRHW = roan (red and white hair)
III. Genetics– B. Genetic Crosses • 5. Polygenic traits – More than one gene will determine phenotype – Hair color in humans is controlled by more than one gene – Eye color in humans also is polygenic – Epistatic traits - one gene exerts control over another gene expression. - Ex: More than 12 pairs of alleles interact in various ways to produce coat color in rabbits. - Ex: 2 gene pairs interact together to produce 8 types of combs in roosters. • 6. Multiple Alleles – More than two alleles are possible for one gene – Example: Blood type » Type A = ―A‖ antigen on the blood cell IA = A allele » Type B = ―B‖ antigen on the blood cell IB = B allele
III. Genetics – C. Genetic Disorders/Diseases • 1. Detection - obtaining fetal cells to do karyotyping and biochemical tests – A) amniocentesis (see next slide) – B) Chorionic villus sampling (see next slide) • 2. Sex-linked traits - genes only found on the X or Y chromosomes – A) colorblindness – B) hemophilia – C) muscular dystrophy – Do a Punnett Square example:• Question: XC Xc•Can 2 normal parents havea colorblind child? If so, what isthe sex of that child? XC XCXC XCXc• A: Yes (If mom is a carrier). Male. Y XCY XcY
III. Genetics– C. Genetic Disorders/Diseases • 4. Gene mutations - changes in DNA sequence caused by exposure to radiation or chemicals, crossing over or genetic errors – Sickle-celled anemia - blood cells are misshaped due conditions of low oxygen » Recessive trait, no known cure – Cystic fibrosis - recessive allele, causes thick mucous build up in the lungs and intestines, can cause liver disease, diabetes » Recessive trait, no know cure – Tay-Sachs - slow degenerative disease of optic and mental function in young children » Recessive trait carried on chromosome 15, no known cure
D. How have humans created new breeds? • Selective Breeding - allowing only those animals with desired characteristics to produce the next generation. • Ex: breeds of dogs, horses, cats, farm animals, crops. • Hybridization - crossing dissimilar individuals to bring together the best of both organisms. Ex: daisies, crops • Inbreeding - continued breeding of individuals with similar characteristics. • Ex: Golden retrievers, Germanwww.vwgs.com/ shepherds • All of the above have been done for years, without altering the genetic code.
IV. DNA Technology– A. Genetic Engineering-making changes in the DNA code • Restriction Enzymes- proteins that ―cut‖ DNA at specific locations, looks for a certain nucleotide (base) sequence • DNA recombination – Cutting and splicing pieces of DNA into other strands of DNA » Plasmids - circular DNA molecules found in bacteria, separate from other bacterial DNA » Sticky ends - matching or complimentary segments of DNA that are produced by restriction enzymes » Human genes can be inserted into bacterial plasmids so the bacteria can produce human enzymes or proteins = recombinant DNA
How restriction enzymes are used to edit DNA:• Enzymes cut the DNA molecule at a certain site.• Different restriction enzymes recognize and cut different sequences ofDNA.• The cut ends are called sticky ends because they may ―stick‖ to othercomplementary bases by means of H bonds.• Can then take a gene from one organism and attach it to the DNA ofanother organism = Recombinant DNA. QuickTime™ and a Cinepak decompressor are needed to see this picture.
• Ex: Genetically Engineered Insulin - Produced by splicing the human gene for making insulin into the plasmid of E.coli host cells.• The genetically modified bacteria then produces insulin; it is collected and used for diabetics.• Was 1st recombinant DNA drug approved for use in humans.• Another Ex: Human Growth Hormone
Example: Steps in producing Human Growth Hormone
Example of Using DNA Technology:DNA Fingerprinting: Process of cutting apart DNA from two sources and comparing the results from gel electrophoresis. Utilized in criminal investigations and paternity/maternity cases. (No individual is exactly alike.) Weblink http://www.pbs.org/wgbh/nova/sheppard/labwave.html
DNA Fingerprinting Procedure:• A small sample of DNA is cut with13-6 Gel enzyme. Figure a restriction Electrophoresis (From sperm, blood, hair, or other material.) Section 13-2• The DNA fragments are separated by size using gel electrophoresis.• The shorter fragments move faster toward the + charge.• Patterns of bands are compared to see if suspect’s band pattern is the same as that of thecrime scene material. DNA plus restriction Power enzyme source Longer fragments Shorter fragments Mixture of DNA Gel fragments
Applications of Genetic Engineering: • Transgenic Organisms - they contain genes from another species • Examples: • tobacco plant which glows in the dark (see top photo)www.mun.ca/.../Luciferase_ reporter_gene.htm • corn which produces a natural pesticide • mice with similar immune systems as humans - are used study effects of diseases • sheep which carry a gene for a human blood protein. They secrete it in their milk - helps patients with cystic fibrosis. (See GM sheep, bottom photo)
More applications of Genetic Engineering: Cloning. Section 13-4 Steps of cloning: A donor cell is taken from a sheep’s udder. Donor Nucleus These two cells are fused using an electric shock. Fused Cell Egg Cell The nucleus of the egg cell is removed. An egg cell is taken The fused cell from an adult begins dividing female sheep. normally. Cloned Lamb Embryo The embryo The embryo is placed develops normally in the uterus of a foster into a lamb—Dolly Foster mother. Mother
Decision Making - Safety and Ethical Issues of DNA Technology: • Can DNA technology create hazardous new pathogens? Could they escape from the lab? • Is genetically modified food safe to eat? • Can transgenic plants pass their new genes to other plants in wild areas? • Who should be allowed to take Human Growth Hormone? • Should we try to eliminate genetic defects in our children? • Should everyone get a DNA fingerprint ID? • Can the Human Genome Project result in human health
Chromosomal Abnormalities and Nondisjunction• Nondisjunction in meiosis results in gametes with abnormal chromosome number• Most cases produce gametes that are not viable
Down Syndrome – Trisomy 21• Extra 21st chromosome• Causes physical and mental abnormalities