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Transcript
Mendelian Genetics 11.1 Gregor Mendel Who was Gregor Mendel? Austrian monk Also “high school” science/math teacher One of the first to use statistics to analyze results Studied garden peas Attempted to refute Blended Inheritance belief What was Mendel’s experimental design? Create true-breed strains Selected for phenotypic traits Genotype vs. phenotype Crossed true-breed plants Kept track of offspring phenotypes What is Mendel’s law of segregation? Traits segregate independently Today we now know What alleles are What a locus is How genotype influences phenotype Why traits segregate independently Remember independent assortment in meiosis I? What is the difference between dominant and recessive? Dominant is phenotypically expressed To be expressed, a recessive must be paired with ________ How can I describe an individual’s genotype? Use capital letter for ____________ allele Use small case letter for _________ allele Homozygous dominant____________ Homozygous recessive_____________ Heterozygote_________________ If a disease, then is a CARRIER What’s the relationship of genotype to phenotype? Genotype _________ phenotype If T = tall and t = short, then TT is a _________ plant Tt is a _________ plant Tt is a _________ plant Mendelian Genetics 11.2 Mendel’s experiments So can you tell me more about Mendel’s monohybrid cross? F1 and F2 generations showed something interesting Ratio: _______ Punnett square What were the F2 offspring like? Ratio: What did Mendel think about this ratio? He determined traits (AKA alleles) are either ________ or _______ What happened when Mendel followed two traits? Dihybrid cross Ratio of cross of two heterozygotes is: Thus, the traits assort ___________ of each other when making gametes Mendelian Genetics 11.3 Solving genetics problems How do we know a trait is dominant (or recessive) in humans? Can’t do breeding experiments like Mendel! Pedigrees Carriers So what do I do with all this information? Solve genetics problems! Use the five steps to solving a genetics problem… What are the five steps to solving a genetics problem? 1. 2. 3. 4. 5. Code the alleles and identify which is dominant/recessive Determine parental (or given) genotypes Determine parental (or given) gametes Draw Punnett square Re-read problem to be sure you are answering the question correctly. Let’s try it! In humans, being able to roll your tongue is dominant (R). If a heterozygous woman marries a man who can’t roll his tongue, what are the chances a child of theirs also won’t be able to roll its tongue? First step… Step 1 Code the alleles and identify which is dominant/recessive In humans, being able to roll your tongue is dominant (R). If a heterozygous woman marries a man who can’t roll his tongue, what are the chances a child of theirs also won’t be able to roll its tongue? Step 2 Determine parental (or given) genotypes In humans, being able to roll your tongue is dominant (R). If a heterozygous woman marries a man who can’t roll his tongue, what are the chances a child of theirs also won’t be able to roll its tongue? Step 3 Determine parental (or given) gametes In humans, being able to roll your tongue is dominant (R). If a heterozygous woman marries a man who can’t roll his tongue, what are the chances a child of theirs also won’t be able to roll its tongue? Step 4 Draw Punnett square In humans, being able to roll your tongue is dominant (R). If a heterozygous woman marries a man who can’t roll his tongue, what are the chances a child of theirs also won’t be able to roll its tongue? Step 5 Re-read problem to be sure you are answering the question correctly. In humans, being able to roll your tongue is dominant (R). If a heterozygous woman marries a man who can’t roll his tongue, what are the chances a child of theirs also won’t be able to roll its tongue? Answer: Now you try! If a homozygous tongue roller and a non-tongue roller marry, what are the chances their child will be able to roll its tongue? USE THE 5 STEPS!!!! Here’s the solution: If a homozygous tongue roller and a non-tongue roller marry, what are the chances their child will be able to roll its tongue? Now practice with the genetics problems… You will be expected to know and use the 5 steps on your exam! Mendelian Genetics 11.4 Human genetic disorders What are autosomal recessive disorders? Autosome = ________ Examples Tay-Sachs disease Cystic fibrosis Phenylketonuria What are autosomal dominant disorders? Only need one copy of the allele to have the disease Examples Neurofibromatosis Huntington’s disease Achondroplasia Mendelian Genetics 11.5 Beyond Mendelian genetics Is complete dominance the only kind of dominance? No! Incomplete dominance Dominant allele cannot fully mask the recessive allele Sickle cell anemia Curly vs. straight hair Is complete dominance the only kind of dominance? Codominance Multiple alleles Blood types demonstrates both What is polygenic inheritance? More than one gene affects phenotype Skin color in humans Human height Eye color Seed color in wheat What is epistasis? One gene affects many traits Marfan Syndrome Defective collagen gene Affects tendons, ligaments, bone, heart tissue, etc. Can environment affect phenotype? Yes! Himalayan rabbits Epigenetics
