Transcript GENETICS
GENETICS THE SCIENCE OF HEREDITY What do you know about genetics? • • • • • • • • • • • • Genes Chromosomes Genome: human genome project Birth defects Mutations Inherited traits Dominant traits DNA Genetic diversity Evolution Gene therapy cloning GENETICS THE SCIENCE OF HEREDITY What do you know about genetics? • • • • • • • • • • • • Genes Chromosomes Genome: human genome project Birth defects Mutations Inherited traits Dominant traits DNA Genetic diversity Evolution Gene therapy cloning Genetic Information • Gene – basic unit of genetic information. Genes are mostly the “recipe’s for proteins. • Genome – the collection of genetic information. A map of where your genes are on your chromosomes • Chromosomes – storage units of genes. Made of DNA. • DNA - is a nucleic acid that contains the genetic instructions mostly for the making of proteins Origins of genetics • Parents know about inheritance by looking at their kids • Farmers know from breeding • Animal breeders know • Gregor Mendel – – – – – 1800’s Austrian monk Studied peas Discovered the laws of genetics Did not know about genes or DNA Gregor Mendel Understanding Physical Anthropology and Archaeology, 8th ed., p. 53 Why peas: give peas a chance • • • • • • 7 easily observed traits Easy to grow Can be self pollinated or cross pollinated Tasty They were growing at the monastery The 7 traits were simple--no combined expression (tall or short, no medium) Mendel’s Peas Mendel’s experiments • Raise pure bred strains – P generation • Cross breed the pure strains to create hybrids – F1 generation • Cross breed the hybrids – F2 generation • Did the experiments thousands of times • Always saw the same ratios – 3 dominant to 1 recessive (phenotype ratio) – 1 DD:2 Dd:1 dd (genotype ratio) • Conclusion: some traits are dominant. They need only one gene to be expressed. Some traits are recessive. They need 2 genes to be expressed. Hybrids look just like the pure dominants. MENDELS LAWS • • Mendel guessed traits were carried by particles he called factors (we call them genes)--PARTICLE THEORY OF INHERITANCE 3 laws 1. Law of dominance--two forms of genes: dominant and recessive alleles. Dominant gene dominates the recessive genes 2. Law of independent assortment--genes for different traits don’t affect each other. *only true if the genes are on separate chromosomes. 3. Law of segregation--two genes for a trait get separated during meiosis VOCAB • Pure bred: breed true, offspring like parents • Hybrid: don’t breed true, offspring mixed • Homozygous: genotype with both genes the same (pure bred-DD or dd) • Heterozygous: genotype with one dominant and one recessive gene (hybrid--Dd) • Genotype: gene combo that produces the visible results (PP, Pp, pp) • Phenotype: visible traits caused by genes (flower color) • Cross: breed critters • Allele: type of gene--dominant (T) OR recessive (t) • Dominant: genes that dominate. Only need one • Recessive: passive genes. Need two. PUNNETT SQUARES • • • • • Prediction tool for genetics--like coin tossing Sometimes called a checkerboard Assumes equal chance of alleles in gametes Female gametes on side, male gametes above Fill in the boxes below and to the right to find the possible genotypes of offspring. • Gives chances of each possibility out of 4. How to find the unknown genotype • Do a test cross – Breed the dominant offspring to a recessive. You always know the genotype of a recessive phenotype. – If any of the offspring have the recessive trait, the dominant parent had to be hybrid – Recessive phenotype only shows up with two recessive genes--one from each parent Probability • The chances are the same for genetics when there are two alleles… • What are the offspring possibilities of a purple (PP) flower and a white flower (pp)? – All offspring are PURPLE! • P1 crosses always result in 100% dominant traits in the F1 Patterns of inheritance • Sex (X) linked traits: found in guys – Genes on the X chromosome – Guys only have one X – They can get recessive traits with one recessive gene – Hemophilia, baldness, color blindness • Co-dominance – Blood types (marker protein on RBC) – Multiple phenotypes – A, B, AB, O (no genes) • Multiple alleles/polygenic traits – Determined by more than one pair of genes – Height, skin color, race, intelligence, personality Genetic counseling • Genetic tests for some disorders • Radiological testing (x-rays) for some disorders • Prenatal testing: amniocentisis • Pedigree charts: genetic family tree Pedigrees • Squares represent males and circles represent females • Horizontal lines connecting a male and female represent mating. • Vertical lines extending downward from a couple represent their children. Interpreting a Pedigree Chart 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 X-linked (23rd Chromosome) If it is a 50/50 ratio between men and women the disorder is autosomal (any of the #1-22 chromosomes) Genetic disorders • Mutations in germ cell (egg or sperm) genes rather than somatic cell genes. • Usually caused by recessive genes • Recessive gene disorders concentrate in small or isolated populations: inbreeding • Some disorders are more common in some ethnic groups: tay sacs, sickle cell, CF. • Few mutations create dominant gene disorders--dwarfism Examples • • • PKU: phenylketonuria – Can’t digest an amino acid Albinism: don’t make melanin Tay Sachs: eastern european jews – – • Cystic fibrosis: carriers may be protected from cholera – – – • • • Fatal for infants recessive Lungs get clogged with mucous Need lung transplant by 30 recessive Sickle cell anemia: carriers protected from malaria – Red blood cells are misshapen in homosygous recessives – African Americans Huntington’s: don’t get symptoms till late in life – Fatal – Dominant Achondroplasia: common form of dwarfism – damonant mutations • Spot mutations: spontaneous – Some are common • Everybody has a couple of mutations! Roughly 1/10,000 genes. You have as many as 30,000 genes. Most go unnoticed and may be beneficial • Mutations make adaptation and evolution possible • Pieces of chromosomes can by lost (deletion), inverted, translocated, or repeated • Non-disjunction is when chromosomes don’t separate during meiosis--may cause trisomy (like trisomy 21-downs syndrome) Genetic applications • • • • • GENE THERAPY DNA FINGERPRINT HUMAN GENOME PROJECT Genetically targeted treatment GMO--genetically modified organisms – Bt corn has a bacteria gene that makes pesticide – Bacteria have been given human genes for making insulin – Human genes have been put in pigs to grow transplant organs – Genes for drugs can be put in fruit and cows/milk • Who owns your genes? • Who controls your genetic information?