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Lecture 5

BIOC15 Lecture 5 Wednesday September 18.doc

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Biological Sciences
Karen Williams

BIOC15 Lecture 5 Wednesday September 18, 2013  Mendel and Genetics: Peas □ Green vs. yellow peas □ Smooth vs. wrinkled □ Tall vs. short □ Brown eyes vs. blue eyes  no longer considered a simple Mendelian trait (appears to be one where B _ vs. bb); many exceptions to colored eyes □ A Mendelian trait - Recessive/ dominant - Heritable (genes as unit of inheritance)  SNPs analysis (last class) □ OCA – mutations in gene important for predisposition to skin cancer □ There are OCA associations with eye color □ Steps you would take to identify the specific OCA2 gene mutation present in patient with melanoma? - Genetic counseling - Pedigrees □ Other SNPs of OCA are associated with eye color in humans  Critical questions about selective breeding before Mendel’s studies □ People have thought about genetics long before Mendel and his Peas □ Monastery people grow fruits and veggies  How does a single gene segregate in a genetic cross □ Although you may breed for a certain coat color (selective breeding); could be related to a particular gene (Transversion mutation)  Mendel studied the inheritance of alternative traits in pea plants □ Knew what went on in the cross (described outcomes) and counted the peas – very important  Mendel’s law of segregation  Mendel’s Laws (principles) □ 2. simple and complete dominance  Garden peas: Pisum sativum  Garden pea (Pisum sativum) □ Wrinkled peas formed  molecular level (textbook)  Genetics involves the study of variation □ Variety of pea characteristics  Mendel’s experiments: Design  Mendel’s experiments: crosses □ You have a parental cross and a F gener1tion which is the progeny □ Reciprocal cross  know  Mendel’s experimental organism: The garden pea □ Cross with plants; cross-pollination  Mendel’s Experiments: F 1 □ Mendel observed that - The F 1as identical to the purple-flowered parent  inheritance of purple (is dominant to white) - Which purple-flowered parent used in the reciprocal cross didn’t matter □ What do these observations indicate about the inheritance of purple flowers  Seed shape □ Round and Wrinkled □ Round is dominant to wrinkled □ Write phenotypes of offspring on the chart □ Write genotypes (know phenotypes); next to each “r” write the probability of getting each of those gametes  Seed shape cross: R plants x r plants  Seed shape: F x F1= F 1ener2tion □ F1all round seeds - F1plants produce gametes are all R r □ Each parent had ½ chance of producing R gametes and ½ chance of producing r gametes □ Mendel counted the seed shapes of the second filial generation (F ) 2 □ F1are heterozygotes at the r locus  Mendel’s explanation □ F1x F 1ross ** □ Particulate as opposed to blending; factors separate and independently combine (random in regards to which allele is being carried)  Seed Shape: F x F self –fertilization 2 2 □ Knowing that the phenotypes of the plants, will they produce all round seeds or a mixture or round and wrinkled seeds (can you tell the genotypes of the plants) □ If they are homozygous for the dominant allele, R, then all the offspring of the self-fertilization should be round  if heterozygous, then 1/3 should be wrinkled and ¾ would be round □ To find the genotype of two similar organisms  self-fertilize and predict what will be the offsprings -  Monohybrid crosses □ F gave us which allele was dominant 1 □ F2gave us whether it was a single factor or not (monohybrid inheritance)  Seed shape: R locus □ When you have heterozygous cross heterozygotes  Quiz F x1wrinkled parent: Test Cross □ Smooth x wrinkled □ Rr x rr □ Symbols: R = smooth, r = wrinkled □ What progeny genotypes would you expect from this test cross - RR, Rr, rR, rr - Rr and rr - All smooth - All wrinkled - Rr  Seed colour □ Heterozygous cross  F 1 green parent: Test cross □ Yellow x green seeds □ Symbols: Yy x yy □ Y = yellow and y = green □ What progeny would you expect from this test cross - YY, Yy, yY, yy - Yy and yy - All green - All yellow - 3 yellow: 1 green  A dihybrids cross produces parental types and recombinant types □ 2 factors (round vs. wrinkled, and yellow vs. green) □ Can be described with each of the two factors □ Process for doing crosses (parents  gametes  F  F 1 2 □ Punnett Square - Top is the male gametes, side is female gametes - Looking at genotypes of offspring, there should be pattern - Looking at phenotypes, there are a few phenotypic classes, some are the same as the parents and some are recombinant (different combinations of what the parents had)  Independent assortment in crosses of F dihybrid1 produces a 9:3:3:1 phenotype ratio □ Expect 2 3:1 ratios together is a 9:3:3:1 ratio □ Write type it looks like, genotype, phenotype, number of progeny you counted with that phenotype (then the ratio) □ When working with an organism, follow Mendel’s procedure (what do I see? Count how many of the phenotype. Is this the sa
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