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Take out a blank sheet of paper On the paper write : 1. your name (first and last) 2. The date today 5/7) 3. The letter of the correct answer to the following question 1. A parent homozygous for Type B blood marries a person with Type AB blood. What is the probability they will have a child with type A blood? A. 0% C. 50% B. 25%. D. 100%. Multiple Alleles Often each allele has its own effect and the alleles are considered codominant. Human ABO Blood type Type Type Type Type A individuals only galactosamine B individuals add only galactose AB individuals add both sugars O individuals add neither sugar Rh Blood Group Rh cell surface marker Epistasis Epistasis - Interaction between products of two genes where one gene modifies the other gene’s phenotypic expression. Emerson - To produce pigment, a Zea mays plant must possess at least one functional copy of each enzyme gene. Epistasis Sex Linkage A trait determined by a gene on the sex chromosome is said to be sex-linked. – In Drosophila, sex is determined by the number of copies of the x chromosome. Eye color gene is carried on the X chromosome What alleles will the sperm have? What alleles will the eggs have? XR XR Y X RX R X RY Xr X RX r X rY Heterozygous for red eye color Offspring phenotypes All females have red eyes ½ of the males have white eyes and ½ the males have red eyes Mutations in Human Heredity Mutations are accidental changes in genes. – Rare, random, and usually result in recessive alleles. Pedigrees used to study heredity. – Hemophilia - Inherited condition where blood is slow to clot or does not clot at all. Only expressed when individual has no copies of the normal allele. Royal Hempohilia - Sex-linked Sickle-Cell Anemia Sickle-Cell Anemia is a recessive inherited disorder in which afflicted individuals have defective hemoglobin, and thus are unable to properly transport oxygen to tissues. Heterozygotes usually appear normal. Homozygotes have Sickle-Cell, but are resistant to malaria. Copyright © McGraw-Hill Companies Permission required for reproduction or display Other Disorders Tay-Sachs – Incurable heredity disorder which causes brain to deteriorates. Nonfunctional form of hexosaminidas A enzyme. Huntington’s Disease – Inherited condition caused by dominant allele causing progressive brain deterioration. Symptoms usually develop late in life. Genetic Counseling and Therapy Process of identifying parents at risk of producing children with genetic defects and assessing genetic state of early embryos. – Amniocentesis – Ultrasound – Chorionic Villi Sampling Pedigree Analysis Mendel’s laws allow us to analyze the genetic information in family records (pedigrees) From this we can determine the nature of alleles that control traits. From this we can: deduce whether the trait is dominant or recessive deduce whether the trait is sex linked deduce the genotypes of members of the family predict the phenotypes of future offspring deduce the genotypes of parents from their offspring phenotypes In a pedigree, each individual is represented by a symbol The shape, color, and location of the symbol carry information about the sex and phenotype of the individual A dominant allele has a different pattern of inheritance: Aa Aa Trait A dominant Only a a for recessive trait expression so both parents have to have a recessive allele Enzymes serve as a catalyst for chemical reactions by lowering the activation energy. Enzymes also function to control the rate of a reaction. Products: less energy content Products: more energy content The laws of thermodynamics dictate that a reaction will not proceed spontaneously unless the molecules that result from the reaction, the products, have lower energy than the molecules that began the reaction, the reactants. An Energy Diagram of a Reaction: a Plot of State Versus Energy A plot of the free energy of the reaction vs the course of the reaction: A reaction is a change A~B C~D of state of matter Original energy state of the reactants Energy Final energy state of the products (exergonic) A-B C-D EA activation energy DG A-C B-D Course of the reaction Spontaneous: Clarification Spontaneous reactions do NOT just go forward immediately to produce products. This is because the reactants must overcome an activation energy, EA. Enzymes Enzymes are protein catalysts that enormously speed up reactions. They often have an “-ase” ending to their name. e.g., hexokinase, catalase, peptidase, mutase They are not themselves changed (except for a brief period of time) and are the same before and after a reaction. Enzymes: 1. Lower the activation energy: this is the MOST important characteristic 2. Do not add or remove energy from a reaction 3. Do not change the equilibrium for a reaction 4. Are reused over and over Enzyme Function DNA – the heredity material Very early it was discovered chromosomes are composed of proteins and DNA. But it took several experiments to conclusively determine specifically which substance made up genes. Griffith Experiment Documented movement of genes from one organism to another (transformation 1928). – Avery Experiment (1944) Removed almost all protein from bacteria, and found no reduction in transforming activity. – Hershey-Chase (1952) Used radioactive isotopes to label DNA and protein. Found genes used to specify new generations of viruses were made of DNA. DNA - genetic material Eukaryotes – DNA located in the nucleus membrane bound organelle Prokaryotes – DNA located in the nucleoid. No membrane surrounded organelle Discovering DNA Structure DNA made up of nucleotides. – Central sugar, phosphate group, and an organic base. Purines - Large bases – Adenine and Guanine Pyrimidines - Small bases – Cytosine and Thymine Nucleotide Base DNA – 4 nucleotide bases 4 base nucleotides Chargaff’s Rule A =T and G=C Discovering DNA Structure Watson and Crick 1953 &( Wilkins) deduced structure of DNA as a double helix. Base pairs linked 5‘ end 3‘ end 3‘ end 5‘ end Double Helix structure two stands of nucleotides Outer part of the ladder is the sugarphosphate backbone Anti-parallel allows for H-bonds between complementary base pairs H- bonds between base pairs 3 H-bonds Packaging DNA in the nucleus DNA Replication Weak hydrogen bonds between base pairs hold DNA strands together. Each chain in the helix is a complimentary mirror image of the other. – Double helix unzips and undergoes semiconservative replication. Confirmed by Meselson-Stahl Experiment. Bi-directional replication Proofreading by DNA polymerase III Genes to Proteins Producing proteins from genes is known as gene expression – DNA - RNA - Protein Gene Expression - Use of information in DNA to direct production of particular proteins. – Transcription - mRNA molecule is synthesized from gene within DNA. – Translation - mRNA used to direct protein production. DNA vs RNA Transcription The RNA copy of a gene used to produce a protein is called messenger RNA (mRNA). Essence of gene expression is reading information encoded within DNA and directing protein production. – Each gene is read from a fixed promoter site where RNA polymerase binds to DNA. – RNA polymerase moves down DNA in threenucleotide steps (Codons). – Each codon corresponds to a particular amino acid. 64 possible codons Transcription Uracil replaces thymine Production of mRNA (messenger RNA) Is all of the DNA expressed? Codons – triplet code Translation – mRNA >> polypeptide Translation – the ribosome Translation – the ribosome Overview of translation