* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Part 5 Intro to Genetics:
X-inactivation wikipedia , lookup
List of types of proteins wikipedia , lookup
Promoter (genetics) wikipedia , lookup
Nucleic acid analogue wikipedia , lookup
Gel electrophoresis of nucleic acids wikipedia , lookup
Genome evolution wikipedia , lookup
Silencer (genetics) wikipedia , lookup
Deoxyribozyme wikipedia , lookup
Point mutation wikipedia , lookup
Molecular cloning wikipedia , lookup
Cre-Lox recombination wikipedia , lookup
Non-coding DNA wikipedia , lookup
Plant breeding wikipedia , lookup
Transformation (genetics) wikipedia , lookup
Endogenous retrovirus wikipedia , lookup
Molecular evolution wikipedia , lookup
Vectors in gene therapy wikipedia , lookup
Community fingerprinting wikipedia , lookup
Part 5 Intro to Genetics: Mendel and his Peas Genetics • Every living organism has traits that they inherit from their parents. • Genetics is the branch of biology that studies heredity. Father of Genetics: • Gregor Mendel was an Austrian monk born in 1822. • After studying math and science, Mendel worked at a monastery as a high school teacher. • In addition to teaching classes, he was responsible for the school’s vegetable garden. Mendel • Mendel knew that pea plants reproduce sexually, meaning the plant contained male parts that made pollen (plant sperm) and female parts that made an ovum (egg.) • When the pollen and ovum unite in fertilization a new plant is produced. • Mendel was curious about the different traits that pea plants Mendel produced. • Pea plants can be tall or short, have purple or white flower, have wrinkled or round peas, and several other noticeable characteristics. • Since peas plants are easy to grow, Mendel used them make observations to study genetics. • The genetic work that Mendel did on pea plants would become the foundation of modern genetics Mendel • Many of the pea plants in the pea garden were true-breeding meaning that if they self pollinated they would produce offspring with the same traits. • Mendel prevented self-pollination by cutting out the male part of the flowers which contained the pollen. Then he would take pollen from a specific flower and apply it to the female part of another pea plant so he knew which plants had been pollinated. Mendel • Mendel fertilized a true-breeding tall plant with a truebreeding short plant. He called these the P generation for parent generation. All of the pea plants that were produced were tall. He called these plants the F1 generation because the Latin words for son and daughter (filius and filia) starts with the letter F. He assumed that the tall trait must be dominant over the short trait. Mendel • Mendel took 2 of the F1 tall plants and fertilized them. The referred to these plants as the F2 generation because they were the 2nd generation produced, or the grandkids. • He expected all tall plants in the F2 generation, but ¼ of the plants produced were short. Although all of the F1 plants were tall, they must have held the information to make a short plant. trait (phenotype) alleles (genotype) P generation F1 generation F2 generation Tall x short all tall 3 tall plants & 1 short TT x tt Tt, Tt, Tt, Tt TT, Tt, Tt, and tt Mendel • Scientist now know that each trait is controlled by the combination of genes we possess. • For each gene, we have 2 versions known as alleles. Some genes are dominant and hide the recessive allele. This explains why there were no short plants in the F1 generation but they reappeared in the F2 generation. Mendel F1 cross: TT x tt • An offspring will get one allele from each parent, so the F1 pea plants received a T from one parent and a t from the other. Together the Tt will make a tall plant, but the plant is a carrier of the short gene t, so it can be given to an offspring to make a short plant in the F2 generation. Genetics Vocabulary • Allele - different form of the gene. There are 2 different types of alleles: (a) Dominant - trait being expressed (capital letter: T = tall) (b) Recessive - trait being masked by the dominant allele (lower case letter: t = short) • Geneotype - what the gene/alleles (“letters”) are. Remember that one allele comes from mom and the other allele from dad. • Autosome - chromosome that determines traits but not gender (in humans, chromosome pairs 1-22) • Sex Chromosome - determines gender (in humans, 23rd pair; XX for females and XY for males) Genetics Vocabulary Continued • Genotype - what the genes/alleles (“letters”) are. The genetic makeup. Genotypes may be either: (a) Homozygous - when an individual has 2 copies of the same allele (ex: TT or tt) (b) Heterozygous - when an individual has different alleles (ex: Tt) • Carrier - individual who is heterozygous for an inherited disorder but does not show symptoms. Carriers can pass the allele to their offspring. • Phenotype - physical expression. The characteristic that you see (ex: tall vs. short; green eyes vs. blue eyes) Punnett Squares Punnett Squares can be used to predict the probability of a trait being passed to an offspring. • Genotype: the combination of letters that represent the alleles • Example: TT, Tt or tt • Results are recorded as probabilities or ratios (homo dominant : heterozygous : homo recessive) • Phenotype: the inherited traits of the offspring that are visible • Example: tall or short • Ratios are reported as (dominant : recessive) Punnett Squares • Monohybrid Cross - involves one trait (ex: Tt x tt). For example, crossing a plant with purple flowers with a plant with white flowers • Dihybrid Cross - involves two traits (ex: TtRr x ttrr) Let’s Practice 1. One cat carries heterozygous, long-haired traits (Ss), and its mate is homozygous for the shorthaired traits (ss). Use a Punnett square to determine the probability of one of their offspring having long hair. P generation: ______ x ______ Genotypic ratio: Phenotypic ratio: Let’s Practice 2. One flower is heterozygous red (Rr) and it is crossed with a homozygous white (rr) plant. Use a Punnett square to determine the probability of one of their offspring having a white color. P generation: ______ x ______ Genotypic ratio: Phenotypic ratio: Let’s Practice 3. In a certain species of pine trees, short needles (S) are dominant to long needles (s). According to your Punnett square, what is the probability of an offspring having short needles if the P generation is true-breeding? P generation: ______ x ______ Genotypic ratio: Phenotypic ratio: Dihybrid (2 factor) Punnett Squares: • Punnett squares can also be used to determine the likely inheritance of multiple traits. Mendel used dihybrid Punnett squares to discover independent assortment; alleles randomly sort into gametes independent of other traits. Dihybrid (2 factor) Punnett Squares: • Steps to complete a dihybrid cross: 1. Create all the possible allele combinations that could be in a gamete RrYy _______________ 2. Place the created gametes on the top and side of square and fill in the squares 3. Label and count each phenotype Dihybrid (2 factor) Punnett Squares: • You could do a tri-hybrid cross to determine the probability of 3 traits at once, but the Punnett square would have 64 boxes. Typically determining the inheritance of any more than 2 traits at once are calculated mathematically without the use of Punnett Squares. Mendel’s Principle’s • Inherited traits are determined by genes which are passed from parents to their offspring. 1. Principle of Dominance: There are 2 forms of each gene, known as alleles. Dominant alleles will be expressed over recessive alleles. 2. Law of Segregation: Gametes (sex cells) only contain one gene for each trait. This means that the offspring will receive one gene from each parent for any characteristic. Example: when F1 plants were crossed to produce the F2 generation, each plant could give either a tall gene or a short gene to the next generation. Mendel’s Principle’s Continued 3. Independent Assortment: Each trait is transmitted separately to the offspring. For example: if a parent pea plant gives a gene for tallness to an offspring, it does not give a gene for green pea color. The gene for color of the pea is inherited independently from the gene for height. • Genes that are on different chromosomes are always independently assorted to the offspring. [Scientist now know that some alleles do move together if they are on located close to each other on the same chromosome]. Beyond Dominant and Recessive: Mendel’s work explained a great deal about inherited traits but it did not explain everything. For many years, scientist have realized that not everything we inherit follows Mendel’s discoveries . Some things are inherited differently. • Incomplete Dominant: neither allele is completely dominant so the heterozygous individual is a blending of the 2 traits: • White flower X Red Flower Pink Flower Beyond Dominant and Recessive: • Codominant: both alleles are dominant, so both are expressed • If the white and red flower were codominant they would produce offspring with both red petals and white petals. • Cat fur on calico cats and human blood type are common examples of codominance. Beyond Dominant and Recessive: • Multiple alleles: some genes have more than 2 alleles. Each individual can only have 2 alleles for each gene, but multiple alleles make more combinations of 2 possible. • Rabbit fur is on 1 gene, but there are 4 alleles that code for fur color. • Polygenic Trait: traits that are based on the interaction of many different genes. Many human genes, including skin, eye, and hair color, are polygenetic. Polygenetic inheritance allows for a greater variety of traits. Human Blood Type: • Human blood type is inherited by codominant alleles and multiple alleles. This lead to confusion for many years. People didn’t understand how a person with type A blood and a person with type B blood could have a baby with type O blood. • Blood type is determined by the presence of an antigen on the surface of red blood cells. A cell can have an A antigen making the person type A, a B antigen makes the person type B, both antigens on the cell makes the person type AB, or if neither antigen is present the person is type O. Human Blood Type: • It is important to only get blood transfusions from an appropriate match, because your immune system will attack any cells containing antigens that it doesn’t recognize. • The genotype of blood is written with an I, not an A and B. This shows that the different alleles are on the same gene. • Type O blood = universal donor • Type AB blood = universal recipient Sex-Linkage • If a trait is autosomal, it will appear in both sexes equally . If a trait is sex-linked, it is usually seen only in males. • Genes that are carried on the X chromosome are called Sex-linked genes because they are inherited with the chromosome that determines gender. • Traits determined by sex-linked genes are called sex-linked traits and can be predicted with Punnett squares using X and Y. Sex-Linkage • Female- (XX) She must have two recessive alleles to express the recessive phenotype. • Male- (XY) He only needs one recessive allele to express the recessive phenotype. Colorblindness X C = Normal X chromosomes Xc=X Chromosome with colorblind gene Y = Normal Y chromosome http://critiquewall.com/2007/12/1 0/blindness Possible Combinations: • XC XC - Woman w/ normal vision • XC Xc - Woman w/normal vision & Carrier for colorblindness • Xc Xc - Colorblind woman • XC Y - Man w/normal vision • Xc Y - Colorblind man *Carrier - Heterozygous for a recessive trait. Colorblind mother Normal Father C Y X X c c X C c C c X X X X Results: c X Y c X Y Colorblind mother Normal Father C X Y X c c X Results: C c C c X X X X c X Y c X Y Female Carriers/ Male colorblind Try the following problems on your paper. Be sure to give the genotypic and phenotypic ratios. Carrier mother Normal Father Y X X X Results: Carrier mother Colorblind Father Y X X X Results: Colorblind mother Colorblind Father Y X X X Results: Normal mother Colorblind Father Y X X X Results: SEX-LINKED DISEASES 1. HEMOPHILIA 2. COLOR BLINDNESS 3. DUCHENE MUSCULAR DYSTROPHY 4. MALE PATTERN BALDNESS Part 6: Genetic Engineering Making changes in the DNA How can a sheep that is 12 years old have an identical twin that is only 4 years old? How many different dog breeds are featured in a dog show? How are new varieties of plants and crops produced? Genetic Engineering • For hundreds of years humans have been manipulating the genetic traits of organisms. This manipulation is called genetic engineering – a technology in which the DNA of a living cell is modified • The oldest form of genetic engineering is selective breeding, where people only allow animals or plants with desired characteristics to reproduce. Through selective breeding, humans have produced many different dog breeds. Dog breeds which are better hunters, companions, etc. Uses of Selective Breeding • Nearly all domestic animals – including horses, cats, dogs and farm animals & most crop plants have been produced by selective breeding. Types of Selective Breeding 1. Hybridization: the selective breeding of 2 dissimilar individuals, so you can have the good traits of both. • Example: freeze resistant plants can be crossed with fruit bearing plants to create fruit plants that can better survive the winter. • Example: combine the disease resistance of one plant with the greater food-producing ability of another to create desirable characteristics a farmer needs to increase food production Types of Selective Breeding 2. Inbreeding: the selective breeding of 2 similar individuals to continue their desired traits. • Example: purebred dogs • Inbreeding will ensure that the characteristics that make each breed unique will be preserved. However, inbreeding will also increases a breed’s susceptibility to diseases and deformities as a cross between these two individuals will more likely bring together 2 recessive alleles for a genetic defect - Example: hip dysplasia in labs and German Sheppards Hip Dysplasia Types of Selective Breeding 3. Inducing mutations through the use of radiation or chemicals. • Bacteria have been mutated to digest oil - used to help clean up oil spills. • Plants have been mutated to produce greater vegetation or to resist insects, cold and drought. • In plant breeding, chemicals have been used to prevent chromosomes from separating during meiosis. As a result, these chemicals have produced cells that have double or triple the number of chromosomes. Plants grown from these cells are called polyploid because they have many sets of chromosomes. Types of Selective Breeding • Polyploid is usually fatal but for some unclear reason, plants can tolerate the extra set of chromosomes. Polyploid can produce a new species of plant that is larger and stronger than their diploid relatives. Many crops such as bananas and citrus fruit have been improved this way. Manipulating DNA Since DNA was first discovered, scientists have learned a lot about DNA and now they are working on ways to change it. We will study a few of the tools scientist use to study DNA but first….. Human Genome Project The Human Genome project first began in 1990 with scientists in the United States and around the world. It had two goals: • Identify and map every gene to its chromosome • Determine the entire DNA sequence for the human gneome. In 2000, all 3.2 billion base pairs of the DNA that makes up the human genome was identified. One of the surprising things about the human genome was the large amount of DNA that does not code for proteins called introns. Scientist discovered that human cells contain only about 30,000-40,000 genes ( that is only double the number of a fruit fly!) Gene Therapy • Information from the human genome is being used to try to find a cure for genetic disorders by gene therapy. In gene therapy, an absent or faulty gene is replaced by a normal gene. Scientists have attempted gene therapy with the use of viruses because of their ability to enter a cell’s DNA. First the virus particles are modified so that they cannot cause disease. Then a fragment of DNA containing the replacement gene is spliced onto the viral DNA. The patient is then infected with the modified virus particles which should carry the gene into the cells to correct genetic defects. To date, gene therapy has not been successful. It still remains as an experimental procedure for diseases such as cystic fibrosis, muscular dystrophy, diabetes and hemophilia. Genetic Research Tools: DNA Fingerprinting: It is a quick and accurate procedure of comparing the DNA sequence of any two organisms. Remember that other than identical twins, no two individuals have the same genetic information. Steps to DNA Fingerprinting: 1. DNA Collection: your DNA is the same in every cell of the body, so it can be gathered from spit, blood, hair follicles, blood, semen, skin or any other substance containing cells. 2. Cutting the DNA: DNA is too long to analyze in one piece, so it needs to be cut up by restriction enzymes. There are hundreds of restriction enzymes and each will cut at a specific place on the DNA sequence. Steps to DNA Fingerprinting: 3.Separating the DNA Pieces by a Process Called GelElectrophoresis: fragments of cut DNA are placed into a special gel which is then placed into an electrophoresis chamber. DNA is a negatively charged molecule so it moves towards the positive end of the chamber when electricity is turned on. Since the gel is thick, the large DNA fragments have a difficult time moving through the gel. At the completion of the gel electrophoresis process, the larger DNA pieces will be near the start and the smaller DNA fragments will have traveled the farthest. Each individual will have a unique pattern of the DNA banding (except identical twins). Gel Electrophoresis The resulting DNA fingerprint (bands) looks like the bar codes used by scanners in stores Uses of DNA Fingerprinting 1. Identify the genes to diagnose inherited disorders. 2. Develop cures for genetic disorders. 3. Criminal cases – forensics 4. Paternity cases 5. Personal identification – used by the U.S. armed forces to identify causalities or persons missing in action. This is better than dog tags or dental records used in the past. Copying DNA with PCR PCR (Polymerase Chain Reaction) is a process where scientists can copy DNA before testing it. Why? A detective finds a single hair as the only evidence of left at the crime scene. Will this hair provide enough DNA to analyze with DNA fingerprinting? More DNA will be needed. It must be replicated and then stored. The DNA is heated to separate the double strand, then cooled to allowed replication to occur. Every cycle of the PCR doubles the amount of DNA. Steps to PCR 1. The double-stranded DNA sample to be copied is heated which separates the strands. 2. When the DNA cools, short pieces of artificially made DNA called primers are added. 3. An enzyme called DNA polymerase and free nucleotides bind to places on the DNA where the copying can begin. The result is two strands of DNA that are identical to each other and the original strand. 4. The heating and replication process is repeated over and over again. Every 5 minutes the sample of DNA doubles again to make many copies in a very short period of time. Copying DNA with PCR: Transgenic organisms: Transgenic Organisms What do you get when you take a sequence of DNA in jellyfish and add it to the DNA of a pig? A transgenic organism! Transgenic organisms: Transgenic Organisms Glowing Pigs! Transgenic organisms: Genetic Engineering allows scientists to transfer DNA from one organisms to another. When an organism contains genes (foreign DNA) other than their own, they are called transgenic. Transgenic plants: one of the 1st transgenic organisms was a tobacco plant that had the gene of a firefly inside. The plant glows in the dark. Many plants now are changed so that they contain pest or drought resistant genes. Transgenic organisms: Transgenic animals: some livestock have been transformed with extra growth hormones so they grow bigger and faster ex: beef cattle, poultry Transgenic bacteria: bacteria can be transformed to make many different human chemicals ex: insulin, human growth hormone, clotting factors Cloning • A clone is an organism that is genetically identical to another. Bacteria naturally clone themselves, but scientists have developed techniques to clone plants and animals. Dolly the sheep was the first mammal successfully cloned in Scotland in 1997 • Dolly was created by transferring genetic material from the nucleus of an adult sheep’s udder cell to an egg whose nucleus (and therefore, its genetic material) had been removed. • Dolly, therefore, carried the DNA of only one parent • Dolly died in 2003, about four years short of a normal’s sheep’s life span • One question that still remains about cloning is how the genetic changes in cells used to obtain the nucleus, might affect the cloned animal’s health Cloning Cloning humans could be possible, but it has not been done yet. Due to ethical and religious concerns, cloning humans is illegal in the United States and most other countries in the world. Stem Cells Humans are made up of trillions of cells, but we each start out as one cell, a zygote, or fertilized egg. The first cells made during development are called stem cells because they can develop into many types of cells; nerve, muscle, skin, blood, or bone. When a stem cell is changed into a specialized cell is called differentiation. Scientist use stem cells in labs to create various tissues to try to cure diseases. Stem Cells In the beginning, stem cells came only from embryos or umbilical chords. Now scientists can use chemicals to create stem cells from other specialized cells by reversing the differentiation process.