BIOL 1107 1nd Edition Lecture 28Outline of Last Lecture I. Genetics II. Mendel’s Law of Segregation III. Law of Independent Assortment Outline of Current Lecture I. Dihybrid CrossII. Mendel’s Rules III. Incomplete DominanceIV. Codominance Current LectureI. 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 Ry rY ryRY RRYY RRYy RrYY RrYyRy RRYy RRyy RrYy RryyrY RrYY RrYy rrYY rrYyry 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 ccWwThese 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.- What about more than two genes?o You use probabilities - Using Probabilities:o Multiplication rule- ANDo Addition rule- ORo Start simple: what is the probability that this individual will produce a gamete with chromosomes ABcD? AaBbccDd ½ chance of getting gametes o Probability of having a homozygous dominant child? (Aa X Aa) ¼o Probability of having a heterozygous child? ¼ + ¼ = ½ o Q: Probability that a child from this cross would be dominant for all traits? AaBbccDdEe X AaBBCCDdEE Dominant -> includes heterozygotes and homozygotes ¾ -> ¼ AA, ½ Aa -> since we didn’t specify hetero/homo, both should be included ¾ X 1 X 1 X ¾ X 1 = 9/16 II. Mendel’s Rules- 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 III. 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 ratioR rR RR Rrr Rr rr IV. 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, themother is A and the child is blood type B. o A: mother’s genotype? Aio Child’s genotype? Bio Father’s genotype? BB or Bi or AB (not
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