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Chapter 14: Human Heredity Thomas Hunt Morgan: studied genetics of fruit flies. Fruit flies are easier to study then humans, they have 8 chromosomes, reproduced quickly, etc In humans: 46 chromosomes (2 sets: 23 from Mom, 23 from Dad) o Chromosome pairs are numbered 1-23, largest to smallest o 22 pairs of homologous chromosomes (similar shape/size) o Autosomes: first 22 pairs of homologous chromosomes (not sex chromosomes) o Sex chromosomes: last pair of chromosomes (23rd pair) X Y (male) or XX (female) Have 50% chance of getting XY, 50% chance of XX Karyotype: picture of chromosomes usually taken during metaphase of mitosis because best time to see them coiled up Tetrad: Pair of homologues chromosomes side by side. 4 chromatids. During Meiosis I these tetrads (homologous pairs) split Pedigree: diagram showing inheritance of a trait through generations. Can use them to determine if a trait is dominant, recessive, autosomal, sex-linked. Sex-linked Trait: a trait carried on the X sex chromosome. Because males only get one X, any X chromosome linked gene a male inherits is expressed. If female has only one X with trait, she is a carrier. Females usually get carrier status from father’s X. Ex: color-blindness – normal color vision is dominant, but if the recessive gene is expressed the person is unable to see certain colors properly. The gene is found on the X chromosome and is 10 times more common in males. Other Sex-linked Traits Hemophilia: Blood clotting disorder, small cuts can be serious. Much more common in males because it is on the X chromosome. Duchenne Muscular Dystropy: 1/3000 males get it between ages 3-6. Genetic disorder that causes muscle weakness because of a defective protein. Looking for cure – insert a dominant allele into muscle cells Human Genetic Disorders Most genes are on autosome chromosomes (chromosomes 1-22) NOT the sex-linked chromosomes Genetic disorders carried on Autosomes: - Albinism: recessive allele on chromosome 11 Not able to produce melanin – no pigment (color) - Cystic Fibrosis: 1/2500 kids have it. Caused by defective protein in cell membrane – results in thick mucus liquid clogs lungs, respiratory issues. - Tay-Sachs Disease: common in Jewish families. Rapid breakdown of nervous system. - PKU – phenylketonuria. Causes mental retardation. Test and treatment for PKU, special diet. - Huntington Disease: Rare disorder carried by a dominant allele on chromosome 4. No symptoms till age 30-40, start lose control of muscles. - Sickle-cell Anemia: blood disorder – RBCs shaped like sickle/crescent. Does not carry as much oxygen in this shape. Painful, lack energy. All of these genetic disorders are carried on autosomes (chromosomes 1-22, not sex chromosomes): Albinism, Cystic Fibrosis, Tay Sachs, PKU, Huntington’s Disease and Sickle Cell Anemia Disorders due to abnormal pairing of chromosomes Non-disjunction: chromosome pairs do not separate correctly, extra or missing chromosomes - Down Syndrome: Extra copy of chromosome 21 – trisomy – 3 chromsomes. Causes mental retardation - Klinefelter Syndrome: Males with extra X chromosome. XXY. Causes mental retardation, sterility, small testes and breast development. - Turner Syndrome: chromosomes don’t separate in meiosis. Sperm or egg produced without sex chromosome. Zygote is XO. Affects only females, sex organs do not develop properly. Heart problems to minor cosmetic issues, small bone growth. Chromosome Deletions: pieces of chromosome break off during meiosis. Chromosome translocation: when pieces of chromosome break off and reattach elsewhere. Affects vary. Prenatal Diagnosis: tests before baby is born - Can test for Down Syndrome, Tay-Sachs, Huntington Disease, etc - Amniocentesis – takes small fluid from amniotic sac surrounding fetus. Looks at cells in the fluid. - Chorionic villus: Tissue of placenta is examined during 1st 10 wks Turning off the X chromosome - Women have XX, do we really need the genes on this extra X if males do fine with just one X? o Most female cells have a Barr body: a condensed turned off X chromosome o One of the X’s gets inactivated, unclear how, perhaps certain genes on that X shut the others off Gene Imprinting Differences in trait based on which parent it comes from Example: A defect on Chromosome 15: - If the defect gene came from dad, child gets Angelman syndrome: causes child to be short and obese - If the defect gene came from mom, child gets Prader-Willi syndrome: child is normal height, thin and hyperactive Ethical Issues with Genetics: Research into genes can help lead to cures, but on the other hand, who should have access to that information? You? Your spouse? Insurance Companies? Human Genome Project - A human cell contains 46 chromosomes that have 3 billion pairs of DNA nucleotides. The Human Genome Project is a worldwide effort to identify the complete nucleotide sequence in humans. - This will help identify genes associated with genetic disorders Manipulating DNA Editing DNA – cut, transplant, rewrite, and/or splice together DNA Cutting tool: biologists can cut DNA using restriction enzymes These enzymes cut DNA at specific nucleotides Separating tool: Electrophoresis Gel – DNA fragments placed in a gel and will separate in gel based on size. Smaller pieces travel faster through gel. DNA FINGERPRINTING Splicing tool: Restriction enzymes cut DNA at certain places and leave some bases exposed. Fragments of DNA can join together on these exposed ends. Chapter 15: Genetic Engineering Breeding Organisms Selective Breeding: organisms with desired characteristics are selected to produce a new generation. Ex: Native Americans bred horses that were strong, fast (desired traits) Also cats, dogs, and crop plants have been selectively bred Hybridization: a cross between two different individuals Ex: Labradoodle – one parent is Labrador other parent a Poodle. Poodle: very intelligent, Labrador: playful, gentle Inbreeding: breeding closely related individuals to maintain traits. Risks – since most members of a breed are genetically similar, more chance of bringing together 2 recessive alleles for a genetic defect. Some inbred dogs end up being blind, have deformities. Biotechnology: application of a technological process or invention to living things. Selective breeding is a form of Biotechnology. Can use is to our benefit by breeding desirable traits – stronger, healthier, more aesthetic, etc - Increases variation, characteristics or options for living things Polyploidy – 3 or more sets of chromosomes - Bananas, oranges from polyploidy plants are bigger and better. . Recombinant DNA: The process of combining DNA from two different sources. Taking DNA from one organism and splicing it/combining it with another organism’s DNA Splicing tool: Restriction enzymes cut DNA at certain places and leave some bases exposed. Fragments of DNA can join together on these exposed ends. Cell Transformation: putting recombinant DNA into a live cell. This will change the cell’s original DNA by adding new DNA to it. Plasmids: small circular pieces of DNA in bacteria and yeast. Scientists attach pieces of DNA to plasmids to carry new DNA into cells. Also, needle injected DNA into cells. Engineering New Organisms Genetic Engineering: cutting and splicing of genes and DNA from different sources. Insert new genes into almost any organism, including humans. Transgenic: organisms that have been transformed with genes from other organisms. Transgenic bacteria engineered to produce amounts insulin (a human protein). The insulin is for diabetics who can’t produce enough insulin. Transgenic cells used to make proteins for treating cancer & other disorders Clone: producing a genetically identical organism from a single cell. Genetic Engineering Manipulating DNA to our benefit. Used to genetically engineer better crops in agriculture, as well as in Human Gene Therapy to help improve health, treating disease, and developing medicine. Human Gene Therapy - It is easier to transform human cells in a lab then in a living person Cystic Fibrosis treatment: transformed viruses by injecting healthy alleles for the Cystic Fibrosis gene into the viruses then sprayed them into patients’ nose/mouth. This helped symptoms, but once those cells with the good genes died off the symptoms started to return. Recent Human Genetics Restriction Fragment Length Polymorphism (RFLP): DNA is cut into small pieces, put through gel, and then a probe is used to identify sequence of nucleotides. Different individuals have different RFLPs in their DNA. Probes identify RFLPs and classify an individual’s DNA. Can test for genetic diseases like: Huntington Disease, Sickle Cell Anemia, Cystic Fibrosis, Tay Sachs, and other diseases using RFLPs to see which alleles you have. RFLPs also used in DNA Fingerprinting / Forensic Science - Identifying RFLPs can distinguish DNA of one individual from another. Blood Types There are 3 alleles for blood Type: A, B, and O – written as IA, IB, I0 A and B are codominant, O is recessive.