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5-17 ATB What are chromosomes composed of? Where do we find chromosomes? Objectives: Discuss sex-linked traits Chromosomes and Inheritance Chapter 12 Review: •Sex chromosomes – •chromosomes that contain genes that determine sex (along with other traits) •Autosomes – •all other chromosomes and the genes they carry Sex-linked traits – traits that are coded by an allele on a sex chromosome Why are there more X sex linked traits? X chromosome is bigger than the y chromosome Linked genes – genes that tend to be inherited together Usually means they are on the same chromosome Mutations Germ-cell mutation – mutations in organisms gametes Somatic cells – organisms body cells Somatic-cell mutation – mutations that occur in organisms body cells Lethal Mutations – mutations causing death (mostly before birth) Some mutations beneficial – leads to natural selection Chromosome Mutations Deletion – loss of a piece of a chromosome (it breaks off) Inversion – chromosome part breaks off and reattaches backwards Translocation – piece of chromosome breaks off and reattaches to a non-homologous chromosome Nondisjunction – chromosome failing to separate during meiosis Get too many, or too few chromosomes (Trisomy 21) aneuploidy – having an abnormal number of chromsomes Chromosome Mutations Gene Mutations Point Mutation – substitution, addition or removal of a single nucleotide in DNA Substitution – when one nucleotide replaces another Insertion Mutation – one or more nucleotide are added to a gene (can lead to a frame-shift mutation) Frame-shift Mutation – deletion of a nucleotide, shifting all the codons, changing all the amino acids Gene Mutations 5-18 ATB What is a somatic cell mutation? Objectives: Practice pedigree problems Human Genetics •Pedigree – •diagram that shows how a trait is inherited over several generations Hemophilia Pedigree from Queen Victoria Carriers – people who carry allele for a disorder, but do not have the disorder (Heterozygous) Genetic disorders – any disease / disorder that have a genetic basis Polygenic – characteristics that are influenced by several genes Examples: Skin color – six genes Other examples – eye color, height, hair color Complex characters – characteristics that are influenced strongly by both environment and genes Sun = darker skin Height = several genes but also nutrition and disease Multiple Alleles – genes that have three or more alleles (usually 2) Example: Blood Type What are the blood types? ABO Three alleles –IA, IB, i Blood Types – A, B, AB, O Antigens – proteins, carbs etc on outside of RBC Antibodies – immuno proteins that destroy unrecognized antigens http://nobelprize.org/educational_games/ medicine/landsteiner/ “Blood typing activity” google – first link Codominance – when both alleles are expressed in the phenotype (IA, IB – neither is dominant over the other – both carbs are produced on cell surface) In codominance, you see both traits Red cow x white cow = roan cow Codominance Incomplete dominance – mix between two parents Example: Straight hair mom x curly hair dad = wavy haired child Red flower x white flower = pink flower In incomplete dominance, you see a mix or blend of both traits Incomplete Dominance 5-19 ATB What is the difference between codominance and incomplete dominance? Objectives: Discuss gene therapy Test Friday / or Monday X-Linked Traits Traits carried on the X chromosome Who will show more X-linked disorders, males or females? Why? Males – b/c they only have one X (Xy) (doesn’t matter if trait is dominant or recessive) Example: Colorblindness – carried on X-chromosome Hemophilia – impaired blood clotting Hemophilia X-linked Hemophilia Pedigree from Queen Victoria X-linked Dominant If mother affected equal chance of sons / daughters affected If father affected All daughters will have, sons ok No carriers possible X-Linked Recessive If mother carrier 50% chance son will be affected, no daughters will have (thou they may be a carrier) If father affected Sons will be ok, daughters have 50% chance of being a carrier) Autosomal Dominant 50 / 50 chance of producing affected children No carriers possible Autosomal Recessive Occurs if both parents are carriers (only 25% of the time) Carriers possible 5-21 ATB What is an X-linked trait? Objectives: Discuss gene therapy Review for test Test / Review sheet – Monday! Single-Allele Traits – traits caused by one dominant allele Huntington’s Disease – caused by one dominant allele. Onset is 3040 so parents have children before they realize the have it Forgetfulness, irritability, muscle spasms and mental illness, then death Genetic testing now beginning to be used to determine if either parent has disease Detecting Genetic Disease Amniocentesis – Dr. removes some amniotic fluid from the sac that surrounds the fetus – can detect over 200 genetic disorders Chorionic Villi Sampling – sample cells that grow between the uterus and placenta Genetic Counseling – process of informing person about their genetic make-up, and problems that may occur Predict likelihood of producing an affected child Treating Genetic Diseases Sometimes treatment only relieves symptoms Phenylketonuria (PKU) – body can’t break down the amino acid phenylalanine into tyrosine – leads to mental retardation Treatment – eliminate the specific amino acid from the diet Cystic Fibrosis – mucus gets lodged in chest – Treatment – 45 minute sessions of pounding on the back to break up mucus Gene Therapy Gene Therapy – technique that places a healthy copy of a gene into the cells of a person with the faulty gene Place the correct gene into the DNA of a virus – introduce modified virus into lungs of person with cystic fibrosis – infects cells, but also brings functional gene – this improves condition, but only as long as those cells survive (not permanent) Somatic Cell Gene Therapy – gene therapy in which body cells are altered Germ Cell Gene Therapy – attempt to alter sperm or eggs – ethical issues – what if it effects the offspring in un-intended ways? The End 5-24 ATB Test Today! Turn in your review sheet Use a pencil You MAY write on the test #13 – “A” should read …(red x white = a flower that is red and white) NOT red and pink #20 --- D. Predict the possible phenotypes of a child born to the F2 son if the son marries a female carrier. It is an X-linked trait http://images.google.com/imgres?imgurl= http://www.sciencecases.org/hemo/chart 2.gif&imgrefurl=http://www.sciencecases. org/hemo/hemo.asp&h=361&w=340&sz= 4&hl=en&start=4&um=1&tbnid=xAG2A_ XDMHy2vM:&tbnh=121&tbnw=114&prev =/images%3Fq%3Droyal%2Bhemophilia %26um%3D1%26hl%3Den%26client%3 Dfirefox-a%26rls%3Dorg.mozilla:enUS:official%26sa%3DG