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Major Concepts for 4th 6 weeks • Mendel Genetics – Slides 2-25 • Pedigrees – Slides 26-36 • DNA and RNA (protein synthesis) – Slides 3773 • Genetic Disorders – Slides 74-78 • Mutations – Slides 79-101 • Genetic Engineering – Slides 102 -117 Mendel Genetics • Objectives: • Predict the outcome of a cross between parents of know genotype. • Determine the probability of a particular trait in an offspring based upon the genotype of parents and the particular mode of inheritance. • Incomplete dominance, co-dominance, multiple alleles, polygenic, complete dominance, and sexlinked Word Wall True-breeding Homozygous Phenotype Physical Trait Tall Gamete Sex Cells – Egg and Sperm Heterozygous Tt Hybrid Genotype The actual genetic make-up Gene TT:Tt:tt Allele 2 Alleles (one from each parent that code for trait) Form of gene (T or t) Big Eyes are dominant = BB or Bb Small eyes = bb Punnett square example Alleles for male Alleles for Female Both parents are heterozygous Yy x Yy Possible Genotypes of Offspring 1 YY:2 Yy: 1 yy Phenotype – 3:1 Cross a homozygous Round with wrinkled R In a Punnett square, the Alleles always move to squares as shown. R r Rr Rr r Rr Rr The actual alleles Physical description of trait Genotype = Phenotype = Probability = RR or Rr= round rr = wrinkled Parents are RR which is same (homozygous) alleles for dominant and rr which are same for recessive trait 4 Rr (heterozygous) 4 round 100% round Cross a hybrid with a hybrid R In a Punnett square, the Alleles always move to squares as shown. r R RR Rr r Rr rr The actual alleles Physical description of trait RR or Rr= round rr = wrinkled Parents are Rr which is heterozygous CLASSIC – Mendel Hybrid Cross Dominant – 75% Recessive – 25% *Determine recessive trait by small number showing the trait Genotype = Phenotype = Probability = 1 RR:2Rr:1rr 3 Round, 1 wrinkled 75% round, 25% wrinkled Independent Assortment • Alleles separate independently during the formation of gametes. The dihybrid cross EeTt x EeTt Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Mendel’s Peas Dihybrid Cross Cross: TtYy x TtYy TY Ty tY ty TTYY TTYy TtYY TtYy Tall, yellow Tall, yellow Tall, yellow Tall, yellow TTYy TTyy TtYy Ttyy Tall, yellow Tall, green Tall, yellow Tall, green TtYY TtYy ttYY ttYy Tall, yellow Tall, yellow TtYy Ttyy Tall, yellow Tall, green TY Notice Phenotype Ratio 9:3:3:1 Ty tY Dwarf, yellow Dwarf, yellow ttYy ttyy ty Genotypes: Phenotypes: 1 TTYY : 2 TTYy Dwarf, yellow Dwarf, green : 4 TyYy : 2 TtYY : 1 TTyy 9 tall plants with yellow seeds : 2 Ttyy : 1 ttYY : 2 ttYy : 1 ttyy 3 tall plants with green seeds 3 dwarf plants with yellow seeds 1 dwarf plant with green seeds Incomplete Dominance Japanese four-o-clock flowers • Red flower plant genotype = RR • White flower plant genotype = WW • Pink flower plant genotype = RW Appear blended. Incomplete, not Full Strength. Cross a Red flower with a White Flower R In a Punnett square, the Alleles always move to squares as shown. R RR = Red WW = white RW = Pink W RW RW W RW RW The actual alleles Physical description of trait Genotype = Phenotype = Probability = 4 RW 4 Pink 100% Pink Parents are RR for red and WW for white. Both are homozygous or true breeding. Co Dominance NOTE: Alleles can be represented different ways. RR for Red, WW for White,RW for Roan or RR for Red, R’R’ for white, and RR’ for Roan. Let’s look at a Punnett Square with both examples. FULL Strength RR x WW = RW or RR X R’R’ = RR’ Roan Cow Cross a Roan cow with white cow. Co-Dominance R In a Punnett square, the Alleles always move to squares as shown. W RR = Red cow WW = white cow RW = Roan Cow W RW WW W RW WW The actual alleles Physical description of trait Genotype = Phenotype = Probability = Parents are RW for Roan which is heterozygous WW which is homozygous for White 2 RW, 2 WW 2 Roan, 2 White 50% Roan, 50% White Cross a Roan cow with white cow. Co-Dominance R In a Punnett square, the Alleles always move to squares as shown. R’ RR = Red cow R’R’ = white cow RR’ = Roan Cow R’ RR’ R’R’ R’ RR’ R’R’ The actual alleles Physical description of trait Genotype = Phenotype = Probability = Parents are RW for Roan which is heterozygous WW which is homozygous for White 2 RR’, 2 R’R’ 2 Roan, 2 White 50% Roan, 50% White Multiple Alleles • When more than two alleles (form of gene) contribute to the phenotype. • Human blood types are an example • There are three possible alleles: A,B, and O • Both A and B are dominant over O. • O is recessive • AB is an example of Co-Dominance 6 different genotypes, 3 different Alleles • • • • • • I AI A I Ai I AI B I BI B Ibi ii Type A - 2 possible genotypes Type AB Type B – 2 possible genotypes Type O Cross a heterozygous type A with homozygous type B Punnett square the Alleles always move to squares as shown. A I i B I A B II B Ii B I A B II B Ii The actual alleles Physical description of trait Genotype = Phenotype = Probability = A = IAIA, IAi B= IBIB, IBi AB =IAIB O = ii IAIB, IBi 2 AB, 2 B 50% AB, 50% B Polygenic traits • Traits controlled by two or more genes. • Lots of variation in trait. • Examples: –Human height, eye and skin color Figure 11.17 Skin Color Autosomal and Sex-Linked Traits • Autosomal - Traits controlled by genes on chromosomes 1 -22. • Sex-Linked – Traits controlled by the X chromosome or the Y chromosome. • Most often sex-linked traits are on the X chromosome. • Let’s look at some of examples and work together. Cross a heterozygous female with a colorblind male n X Y Female = XX Male = XY Normal = N, colorblind = n N X N n X X N X Y Xn n n XX n XY The actual alleles Genotype = Phenotype = Physical description of trait Probability = Work like any other Punnett Square. Remember no letter on the Y. The trait is connected to the X! XNXn,XnXn,XNY,XnY 2 Females, 1 Normal, 1 Color-blind 2 Males, 1 Normal, 1 Color-blind 50% Colorblind Test Your Knowledge of Punnett Square • http://www.biology.clc.uc.edu/courses/bio10 5/geneprob.htm Sex Cells (Gametes) from Meiosis 1N EGG Pedigrees • Apply pedigree data to interpret various modes of genetic inheritance. A pedigree is a chart of the genetic history of family over several generations. Scientists or a genetic counselor would find out about your family history and make this chart to analyze. Symbols in a Pedigree Chart • Normal Female • Affected female Female carrier Not all Female is represented by a circle pedigrees show carriers Normal Male Affected Male Male carrier – Not possible in Sex-linked traits (if you see carrier male, it is autosomal) Male is represented as a square What does a pedigree chart look like? X NY X NX n 1st X NX N generation X nY 2nd generation 3rd generation •Does this pedigree show a sex-linked trait? •Yes, males are affected more than females, and females are carriers. •How many children were born in generation 2 to couple with affected male? •3, 2 boys and a girl. •What is the genotype of the female in generation 3? •XNXN •What are genotypes for generation 1? If carriers are not shown, genotype could be homozygous or heterozygous even though trait is not shown. X NY XNXN or XNXn XNXN or 1st generation X NX n X nY 2nd generation 3rd generation This is the same pedigree without female carriers being shown. The large affect it has on males, tells us it is sex-linked and since it is not showing up in females, it is recessive. NOT all pedigrees will show carriers, so be careful with analyzing! Interpreting a Pedigree Chart 1. Determine if the pedigree chart shows an autosomal or X-linked disease. – If most of the males in the pedigree are affected the disorder is most likely X-linked – If it is a 50/50 ratio between men and women the disorder is most likely autosomal • When interpreting a pedigree chart of a family with a disease like muscular dystrophy, it is important to consider two steps. The first is to determine if the disorder is autosomal or X-linked. • If the disorder is X-linked most of the males will have the disorder because the Y-chromosome cannot mask the affects of an affected X-chromosome. A female can have the disorder, but it would be a very low percentage. For a female to be affected, she would have had to receive an affected gene from both the mother and the father. This means that the father would have the disorder and the mother was a carrier. • In an autosomal disorder, the disorder is not found on the X or Y chromosome. It is found on the other 22 chromosomes in the human body. This means that men and women have an equal chance of having the disorder. Is it Autosomal or X-linked? Autosomal because it affects males and females equally Interpreting a Pedigree Chart 2. Determine whether the disorder is dominant or recessive. – If the disorder is dominant, one of the parents must have the disorder. – If the disorder is recessive, neither parent has to have the disorder because they can be heterozygous. It is important to find out if a disorder is dominant or recessive. For example, Huntington’s disease is a dominant disorder. If you have only one dominant gene you will have Huntington’s disease, which is a lethal disorder. The disorder does not show up until a person is in their middle ages such as 45. It will quickly decrease their motor skills and the brain will begin to deteriorate. • If a disorder is dominant, one parent must have the disorder (either homozygous dominant (TT) or heterozygous recessive (Tt). Both parents do not have to have the disorder. One parent might not have the disorder or be a carrier. If a disease is dominant, it does not skip a generation unless one parent is heterozygous dominant (Tt) and the other parent is homozygous recessive (tt). In this case the child has a chance of not receiving the dominant gene. • If the disorder is recessive, a parent does not have to have the disorder, but could still pass it to their offspring. This would happen when a parent is heterozygous recessive (Tt) and passes on the recessive (t) gene. This means this disorder can skip generations. An example of a recessive disorder would be sickle cell anemia. Dominant or Recessive? It is dominant because a parent in every generation has the disorder. Remember if a parent in every generation has the disorder, the disorder has not skipped a generation. If the disorder has not skipped a generation, the disorder is dominant. Practice Analyzing Pedigrees • http://www.zerobio.com/drag_gr11/pedigree /pedigree_overview.htm Dominant or Recessive? It is recessive, because a parent in every generation does not have the disorder. If a disorder Skips a generation, then the disorder is recessive. If a carrier is shown, it is recessive also. Scientists call this the: DNA RNA Protein DNA Nucleotide Deoxyribose Nucleic Acid Phosphate Group O O=P-O O 5 CH2 O N C1 C4 Sugar (deoxyribose) C3 C2 Nitrogenous base (A, G, C, or T) Watson and Crick constructed a Model of DNA showing the double helix. • James Watson and Francis Crick worked out the three-dimensional structure of DNA, based on work by Rosalind Franklin Figure 10.3A, B DNA Double Helix “Rungs of ladder” Nitrogenous Base (A,T,G or C) “Legs of ladder” Phosphate & Sugar Backbone Chargaff’s Rule • Adenine must pair with Thymine • Guanine must pair with Cytosine • Their amounts in a given DNA molecule will be about the same. T A G C DNA Nucleotides joined together DNA Double Helix 5 O 3 Notice base pairing A+T G+C 3 P 5 O C G 1 O P 5 3 2 4 4 2 3 P 1 T 5 A P 3 O O P 5 O 3 5 P The Code of Life… • The “code” of the chromosome is the SPECIFIC ORDER that bases occur. Proteins are built from the code. A T C G T A T G C G G… DNA Replication • DNA must be copied so new cells will have complete instructions for making the RIGHT proteins. • The DNA molecule produces 2 IDENTICAL new complementary strands following the rules of base pairing: A-T, G-C •Each strand of the original DNA serves as a template for the new strand Each DNA molecule contains one original and one new complementary strand DNA Replication • Complementary base pairs form new strands. • …DNA control cell functions by serving as a template for PROTEIN structure. • RNA uses base pairing, but the T is replaced with U for Uracil. A + U, G + C • 3 Nucleotides = a triplet or CODON (which code for a specific AMINO ACID • AMINO ACIDS are the building blocks of proteins. • Proteins regulate cell activity and express traits controlled by genes. DNA – Blueprint for Life DNA RNA – Ribosome – Amino Acid Protein Trait Expresses Trait Protein Synthesis – Building Proteins DNA contains the instructions for the proteins that are needed for life. If the DNA does not replicate correctly, the wrong protein could be made. DNA and RNA Comparison Double Strand Single Strand A+T G+C A+U G+C Both have Phosphate Deoxyribose Ribose DNA always STAYS in Nucleus RNA is in nucleus during transcription, moves in cytoplasm, and on ribosome during translation. Table 14.2 Types of RNA Type of RNA Functions in Messenger RNA (mRNA) Nucleus, migrates to ribosomes in cytoplasm Transfer RNA (tRNA) Cytoplasm Provides linkage between mRNA and amino acids; transfers amino acids to ribosomes Ribosomal RNA (rRNA) Cytoplasm Structural component of ribosomes Function Carries DNA sequence information to ribosomes DNA makes RNA during Transcription • DNA can “unzip” itself and RNA nucleotides match up to the DNA strand. • Both DNA & RNA are formed from NUCLEOTIDES and are called NUCLEIC acids. • The information constituting an organism’s genotype is carried in its sequence of bases – The DNA is transcribed into RNA, which is translated into the polypeptide DNA TRANSCRIPTION RNA TRANSLATION Protein Figure 10.6A Transcription produces genetic messages in the form of mRNA RNA polymerase RNA nucleotide Direction of transcription Template strand of DNA Figure 10.9A Newly made RNA RNA polymerase • In transcription, DNA helix unzips – RNA nucleotides line up along one strand of DNA, following the base-pairing rules – single-stranded messenger RNA peels away and DNA strands rejoin DNA of gene Promoter DNA Initiation Elongation Terminator DNA Area shown in Figure 10.9A Termination Growing RNA Completed RNA Figure 10.9B RNA polymerase Eukaryotic RNA is processed before leaving the nucleus • Noncoding segments, introns, are spliced out • A cap and a tail are added to the ends Exon Intron Exon Intron Exon DNA Cap RNA transcript with cap and tail Transcription Addition of cap and tail Introns removed Tail Exons spliced together mRNA Coding sequence NUCLEUS CYTOPLASM Figure 10.10 RNA builds Proteins from Amino Acids during Translation • The cell uses information from “messenger” RNA to produce proteins mRNA leaves the nucleus to go to ribosome Amino Acids tRNA Anti-codon Proteins – Express Traits codon rRNA and tRNA translate The message to make proteins Translation of nucleic acids into amino acids • The “words” of the DNA “language” are triplets of bases called codons • The codons in a gene specify the amino acid sequence of a polypeptide • RNA Transcription copies the DNA onto mRNA. • Translation takes place in the cytoplasm on the ribosomes. • tRNA picks up the correct amino acid and builds a protein on the rRNA from the mRNA. Types of RNA • mRNA contains codons which code for amino acids. 3 Letter Code for amino acids What amino acid will the code CAU make? His Virtually all organisms share the same genetic code “unity of life” Second Base C U UUU UUC UUA UUG C CUU CUC CUA CUG A AUU AUC ile AUA AUG met (start) ACU ACC ACA ACG G GUU GUC GUA GUG GCU GCC GCA GCG phe leu leu val UCU UCC UCA UCG CCU CCC CCA CCG A ser UAU UAC UAA UAG pro CAU CAC CAA CAG thr AAU AAC AAA AAG ala GAU GAC GAA GAG G tyr stop stop his gln asn lys asp glu UGU UGC UGA UGG CGU CGC CGA CGG AGU AGC AGA AGG GGU GGC GGA GGG 64 possible combinations – 20 specific amino acids cys stop trp arg ser arg gly U C A G U C A G U C A G U C A G Third Base First Base U What signals the ribosome to start translating the mRNA Into a new amino acid sequence and signals it to stop? An initiation codon marks the start of an mRNA message AUG = methionine Start of genetic message End Figure 10.13A • An exercise in translating the genetic code Transcribed strand DNA Transcription RNA Start codon Polypeptide Translation Stop codon Figure 10.8B Gene 1 Gene 3 DNA molecule Gene 2 Proteins are built from chains of amino acids DNA strand TRANSCRIPTION RNA Codon TRANSLATION Polypeptide Amino acid Ribosomes build polypeptides (chain of amino acids) Next amino acid to be added to polypeptide Growing polypeptide tRNA molecules P site A site Growing polypeptide Large subunit tRNA P A mRNA mRNA binding site Codons mRNA Small subunit Figure 10.12A-C • mRNA, a specific tRNA, and the ribosome subunits assemble during initiation Large ribosomal subunit Initiator tRNA P site A site Start codon mRNA 1 Figure 10.13B Small ribosomal subunit 2 Amino acid Polypeptide A site P site Anticodon mRNA 1 Codon recognition mRNA movement Stop codon New peptide bond 3 Translocation 2 Peptide bond formation Figure 10.14 Overview of Protein Synthesis • Let’s look at it ONE more time! TRANSCRIPTION DNA mRNA RNA polymerase Stage 1 mRNA is transcribed from a DNA template. Amino acid TRANSLATION Enzyme Stage 2 Each amino acid attaches to its proper tRNA with the help of a specific enzyme and ATP. tRNA Initiator tRNA mRNA Figure 10.15 Anticodon Large ribosomal subunit Start Codon Small ribosomal subunit Stage 3 Initiation of polypeptide synthesis The mRNA, the first tRNA, and the ribosomal subunits come together. New peptide bond forming Growing polypeptide Codons Stage 4 Elongation A succession of tRNAs add their amino acids to the polypeptide chain as the mRNA is moved through the ribosome, one codon at a time. mRNA Polypeptide Stop Codon Figure 10.15 (continued) Stage 5 Termination The ribosome recognizes a stop codon. The polypeptide is terminated and released. DNA – Blueprint for Life DNA RNA – Ribosome – Amino Acid Protein Trait Expresses Trait 1. Why is transcription necessary? Transcription makes messenger RNA (mRNA) to carry the code for proteins out of the nucleus to the ribosomes in the cytoplasm. 2. Describe transcription. RNA polymerase binds to DNA, separates the strands, then uses one strand as a template to assemble mRNA. 3. Why is translation necessary? Translation assures that the right amino acids are joined together by peptides to form the correct protein. 4. Describe translation. The cell uses information from mRNA to produce proteins. The tRNA brings the right amino acid to ribosome, rRNA to produce a specific amino acid chain that will later become an active protein. 5. What are the main differences between DNA and RNA. DNA has deoxyribose, RNA has ribose; DNA has 2 strands, RNA has one strand; DNA has thymine, RNA has uracil. 6. Using the chart on page 303, identify the amino acids coded for by these codons: UGG CAG UGC tryptophan-glutamine-cysteine Genetic Disorders Autosomal Recessive Normal = N Genetic Disorders nn = cystic fibrosis Both parents Must be Carriers Nn X Nn Sickle Cell Anemia Autosomal recessive Both parents must be carriers To pass to children. Nn X Nn Or one is carrier and other has condition. Nn x nn Would not show in parents if Carriers Tay-Sachs Autosomal Recessive Huntingdon’s Disease Autosomal Dominant What Are Mutations? • Changes in the nucleotide sequence of DNA • May occur in somatic cells (body cells,aren’t passed to offspring) • May occur in gametes (eggs & sperm) and be passed to offspring • May be chromosomal or gene mutations. DNA – If there is a mutation in the DNA strand, then the RNA strand will be changed DNA If the mRNA brings the wrong instructions, may result in Gene wrong protein – Ribosome – Amino Acid Protein Many mutations do not change the amino acid, so NO mutation will occur. Trait Expresses Trait Mutation – wrong protein Protein Translation • Modified genetic code is “translated” into proteins • Codon code is specific, but redundant! – 20 amino acids – 64 triplet (codon) combinations Which is why some mutations don’t matter! Gene Mutations • Change in the nucleotide sequence of a gene • May only involve a single nucleotide • May be due to copying errors, chemicals, viruses, etc. Point Mutation • Change of a single nucleotide • Includes the deletion, insertion, or substitution of ONE nucleotide in a gene • Sickle Cell disease is the result of one nucleotide substitution • Occurs in the hemoglobin gene Frameshift Mutation • Inserting or deleting one or more nucleotides • Changes the “reading frame” like changing a sentence • Proteins built incorrectly Normal hemoglobin DNA mRNA Mutant hemoglobin DNA mRNA Normal hemoglobin Sickle-cell hemoglobin Glu Val Example of Sickle Cell mutation • Illustration of mutations NORMAL GENE mRNA Protein Met Lys Phe Gly Ala Lys Phe Ser Ala BASE SUBSTITUTION Met Missing BASE DELETION Met Lys Leu Ala His Figure 10.16B •Chromosomal changes can be large or small Deletion Homologous chromosomes Duplication Inversion Reciprocal translocation Nonhomologous chromosomes Figure 8.23A, B Chromosome Mutations • May Involve: – Changing the structure of a chromosome – Can cause abnormal development of offspring. of part Deletion • Due to breakage • A piece of a chromosome is lost Inversion • Chromosome segment breaks off • Segment flips around backwards • Segment reattaches Duplication • Occurs when a gene sequence is repeated Translocation • Involves two chromosomes that aren’t homologous • Part of one chromosome is transferred to another chromosomes Nondisjunction • Failure of chromosomes to separate during meiosis • Causes gamete to have too many or too few chromosomes • Disorders: – Down Syndrome – three 21st chromosomes – Turner Syndrome – single X chromosome – Klinefelter’s Syndrome – XXY chromosomes Normal Male Karotype 2n = 46 96 Normal Female Karotype 2n = 46 97 Male, Trisomy 21 (Down’s) Can you spot the problem? 2n = 47 98 Female Down’s Syndrome 2n = 47 99 Klinefelter’s Syndrome 2n = 47 100 Genetic Engineering • Evaluate the scientific and ethical issues associated with gene technologies. • Genetic Engineers refers to the alteration of an organism’s genes for practical purposes. • Recombinant DNA • Transgenic Organisms • Cloning • Stem Cell Research • Gel Electrophoresis/DNA fingerprinting Recombinant Bacteria 1. Remove bacterial DNA (plasmid). 2. Cut the Bacterial DNA with “restriction enzymes”. 3. Cut the DNA from another organism with “restriction enzymes”. 4. Combine the cut pieces of DNA together with another enzyme and insert them into bacteria. 5. Reproduce the recombinant bacteria. 6. The foreign genes will be expressed in the bacteria. Benefits of Recombinant Bacteria 1. Bacteria can make human insulin or human growth hormone. 1. Bacteria can be engineered to “eat” oil spills. Recombinant DNA • The ability to combine the DNA of one organism with the DNA of another organism. • Recombinant DNA technology was first used in the 1970’s with bacteria. Genetically modified organisms are called transgenic organisms. TRANSGENIC ANIMALS 1. Mice – used to study human immune system 2. Chickens – more resistant to infections 3. Cows – increase milk supply and leaner meat 4. Goats, sheep and pigs – produce human proteins in their milk Transgenic Goat Human DNA in a Goat Cell Carries a foreign gene that has been inserted into its genome. . This goat contains a human gene that codes for a blood clotting agent. The blood clotting agent can be harvested in the goat’s milk. How to Create a Transgenic Animal Desired DNA is added to an egg cell. The DNA of plants and animals can also be altered. PLANTS 1. disease-resistant and insect-resistant crops 2. Hardier fruit 3. 70-75% of food in supermarket is genetically modified. How to Create a Genetically Modified Plant 1.Create recombinant bacteria with desired gene. 2. Allow the bacteria to “infect" the plant cells. 3. Desired gene is inserted into plant chromosomes. DNA Cloning • Transfer of DNA fragment from one organism to a selfreplicating genetic element such as bacterial plasmid Reproductive Cloning • Generate an animal that has the same nuclear DNA as another existing animal. Therapeutic Cloning • Also called “embryo cloning”, is the production of human embryos for use in research. • Stem Cell Collection: • Are unspecialized cells capable of renewing themselves through cell division. • Under certain experimental conditions, they can be induced to become tissue or organ specific cells with special functions. What do you think about eating genetically modified foods? Polymerase Chain Reaction PCR • PCR allows scientists to make many copies of a piece of DNA. 1. Heat the DNA so it “unzips”. 2. Add the complementary nitrogenous bases. 3. Allow DNA to cool so the complementary strands can “zip” together. Steps Involved in Gel Electrophoresis 1. “Cut” DNA sample with restriction enzymes. 2. Run the DNA fragments through a gel. 3. Bands will form in the gel. 4. Everyone’s DNA bands are unique and can be used to identify a person. 5. DNA bands are like “genetic fingerprints”.