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# UT BIO 325 - Mendelian Gentics

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BIO 325 1st Edition Lecture 2Outline of Last Lecture I. Introduction to GeneticsOutline of Current Lecture I. Simple ProbabilityII. Mendelian GeneticsCurrent LectureI. Before Mendel genetics was based largely on artificial selectiona. Keeping and propagating individuals that have the most desirable traitsII. Prevailing theories of geneticsa. The homunculusb. Blended inheritanceIII. Probability= The #/times an event is expected to happen/ The # of opportunities for thatevent to happena. The product rule: The probability of 2 independent events occurring simultaneously is the product of each of those probabilitiesi. Ex: probability of rolling two diceand they both be fours1. (1/6) x (1/6) = (1/36): Probability of first event x Probability of secondb. The sum rule: The probability of either one of two mutually exclusive outcome occurring is the sum of their individual probabilitiesi. Ex: probability of rolling a four or a five on a single roll of a die?1. (1/6) + (1/6)= (1/3): Probability of first event + Probability of secondIV. Mendelian Geneticsa. Why was Mendel successful?1. Chose a great model systema. Garden pea was a perfect flower: male and female organs on same flowerb. Easy to cross-fertilizec. Large # of offspringd. Grew well in Brno2. Chose 7 great traitsThese 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.a. Clear cut alternate forms (either yellow or green, either round or wrinkled) No intermediateb. Discrete (not continuous) traits3. Began with pure-breeding linesa. A yellow pea only gave rise to yellow peas through self-fertilizationb. Same for purple-flowered peas, wrinkled peas, etc.4. Mendel carefully controlled the matingsa. Knew parents with certaintyb. Performed reciprocal crosses (ex: male yellow with female green but also female yellow with male green)Showed thatwhich parent contributed the egg/sperm did not matter i.e. disproved the homunculus theory. 5. Mendel worked with large numbers of plantsV. Key Termsa. Monohybrid cross- Cross between 2 plants that differ by a single traiti. Dominant trait- The trait seen in the F1 generationii. Recessive trait- The trait not visible in the F1 generation iii. Results in a 1:2:1 genotypic ratio and a 3:1 phenotypic ratiob. Parental generation- Original pure-breeding linesc. First Fillial generation (F1)- Offspring resulting from the original monohybrid cross*Childrend. Second Filial generation (F2)- Offspring from the self-fertilization of the F1 generation *Grandchildren VI. Blending is disproved by the fact that the recessive trait (green pea) is not lost in the F1 generation, but reappears in the F2 generation; in a 3:1 ratio; so the green pea trait wasn’t blended away after all. VII. Mendel’s Modela. Mendel’s Law of Segregation (1st law)i. For each trait, there are two copies (alleles) of a unit of inheritance (genes). During reproduction, the units separate and the egg or sperm (gamete) only contains one of these unitsii. Homozygous- individuals that contain two identical alleles; pure-breedingiii. Heterozygous- individuals that contain two different allelesPunnett square: illustrates possible combinations of alleles that can ariseTest cross- Distinguishing between an unknown YY pure-breeding from aYy hybrid by pairing with a yy homozygous recessive and observing the offspring.VIII. Dihybrid Crossesa. Mendel’s law of independent assortment: During gamete formation, different pairs of alleles segregate independently of each otherb. Results in 9:3:3:1 ratioUse of the product and sum rule to determine probabilities for

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