BIOL 1107 1nd Edition Lecture 28 Outline of Last Lecture I Genetics II Mendel s Law of Segregation III Law of Independent Assortment Outline of Current Lecture I Dihybrid Cross II Mendel s Rules III Incomplete Dominance IV Codominance Current Lecture I Dihybrid Cross a dihybrid cross is a cross between F1 offspring first generation offspring of two individuals that differ in two traits of particular interest Ratios know this for the exam o 9 double dominant yellow round o 3 first dominant second recessive yellow wrinkled o 3 first recessive second dominant green round o 1 double recessive green wrinkled RY RRYY RRYy RrYY RrYy RY Ry rY ry Ry RRYy RRyy RrYy Rryy rY RrYY RrYy rrYY rrYy ry RrYy Rryy rrYy rryy Q A sexually reproducing animal complete question on elc New o A 1 HT one for each gene Q In cocker spaniel dogs o A 2 3 16 we use ratio discussed in class one dominant one recessive Q In mice the allele o A 2 CCWw X ccWw These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute II Mendel s Rules III What about more than two genes o You use probabilities Using Probabilities o Multiplication rule AND o Addition rule OR o Start simple what is the probability that this individual will produce a gamete with chromosomes ABcD AaBbccDd chance of getting gametes o Probability of having a homozygous dominant child Aa X Aa o Probability of having a heterozygous child o Q Probability that a child from this cross would be dominant for all traits AaBbccDdEe X AaBBCCDdEE Dominant includes heterozygotes and homozygotes AA Aa since we didn t specify hetero homo both should be included X 1 X 1 X X 1 9 16 Traits controlled by particles Particles come in pairs Different particles can promote different traits If two different particles in the same organism one covers up the other Particles separate during gamete formation law of segregation Different pairs of particles sort into gametes independently of each other law of independent assortment Mendel was lucky Incomplete dominance With incomplete dominance a cross between organisms with two different phenotypes produces offspring with a third phenotype that is a blending of the parental traits RR X rr RR red rr white Rr pink below 1 2 1 ratio IV R r R RR Rr r Rr rr Codominance With codominance a cross between organisms with two different phenotypes produces offspring with a third phenotype in which both of the parental traits appear together Blood type A B AB O Genotype for A IA IA IA I for B IB IB IB I for AB IA IB for O i i Only 1 gene controls blood group but 4 alleles exist You can only get two alleles one from mom and one from dad What do genes encode for Enzyme O group has no enzymes Q Blood typing is often used as evidence in paternity testing In one case the mother is A and the child is blood type B o A mother s genotype Ai o Child s genotype Bi o Father s genotype BB or Bi or AB not O
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