Mendel - Mendelian Genetics Genetics Mendel’s Genetics...

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Unformatted text preview: Mendelian Genetics Genetics Mendel’s Genetics Experiment Experiment s with Peas Pea Characters Investigated Pea Genetic Loci & Alleles Genetic allele for purple flowers gene locus for flower color allele for white flowers Genetic Recombination at Fertilization Genetic Mendel’s Test for Evaluating the Inheritance of Seed Shape in Pea Plants Plants q Recognized Recognized two different traits for the seed shape character in pea plants: round versus wrinkled seeds. round q Established true-breeding varieties Established for each of these traits. for Mendel’s Test for Evaluating the Inheritance of Seed Shape in Pea Plants Plants q Crossed Crossed true-breeding round seed variety with the true breeding wrinkled seed variety (this represents the Parental, or P, cross). the q Offspring (F1 generation) are called “hybrids”. “hybrids”. Mendel’s Test for Evaluating the Mendel’s Inheritance of Seed Shape in Pea Plants Plants q 100% 100% of these hybrids produced round seeds. q Crossed these F1 generation hybrids among each other (individual crosses being selected at random). crosses Mendel’s Test for Evaluating the Mendel’s Inheritance of Seed Shape in Pea Plants Plants q Results for their offspring (F2 generation): generation): ¸5474 (74.7%) were plants that 5474 produced round seeds. produced Mendel’s Test for Evaluating the Mendel’s Inheritance of Seed Shape in Pea Plants Plants q Results for their offspring (F2 generation): generation): ¸1850 (25.3%) were plants that 1850 produced wrinkled seeds. produced Mendel’s Test for Evaluating the Mendel’s Inheritance of Seed Shape in Pea Plants Plants q Results for their offspring (F2 generation): ¸ Ratio of round:wrinkled = approx. 3:1 Mendel’s Explanation for his Results Results q q For every character (e.g., seed shape) For an individual possess two instruction sets (alleles). sets One of these alleles was originally One derived from the individual’s mother, the other allele being originally derived from the individual’s father. the Mendel’s Explanation for his Results Results q In In true-breeding individuals, both alleles are the same. alleles q Hybrids, on the other hand, have Hybrids, one of each kind of allele. one Mendel’s Explanation for his Results Results q Mendel Mendel believed that only two alleles were possible for a given genetic character, and that one of the alleles (the dominant one) masked the expression of the other (the recessive one) in the hybrid. recessive Mendel’s Explanation for his Results Results q When When the hybrid formed gametes, only one of the two possible alleles would end up in a gamete. would q However, both alleles possessed an However, equal chance of appearing in a gamete. gamete. Mendel’s Explanation for his Results Results q Defining alleles: R = the round allele (dominant). r = the wrinkled allele (recessive). Mendel’s Explanation for his Results Results q Defining genotypes & their phenotypes: RR genotype (homozygous dominant) = round phenotype. round rr genotype (homozygous recessive) = wrinkled phenotype. wrinkled Rr genotype (heterozygous) = round phenotype phenotype Pea Shapes Pea RR Rr rr Mendel’s Explanation for his Results Results Parental (P) Cross Round X Wrinkled Round RR rr Gametes: R r Mendel’s Explanation for his Results Results F1 Generation Hybrids 100% Round 100% Rr Mendel’s Explanation for his Results Results F1 Generation Cross Round X Round Rr Rr Gametes: R r Rr Mendel’s Explanation for his Results Results F1 Gametes: R r Rr 2 F Generation Outcome Round Wrinkled Round RR Rr Rr rr RR Note: 3:1 ratio of round:wrinkled Punnett Square Diagram Punnett Rr gametes R Rr r Rr rr R RR r Rr Mendel’s Law of Segregation Segregation In the formation of gametes, In two members of a gene pair (alleles) segregate into different haploid gametes with equal probability. equal A Testcross Testcross F1 Hybrids (Rr) x F2 Recessives (rr) Punnett Square Diagram for Testcross Testcross Rr x rr gametes R Rr r rr rr r Rr Mendel’s Law of Independent Assortment Independent Whenever two or more pairs of Whenever contrasting characters are brought together in a hybrid, the alleles of the different pairs segregate independently of one another during gamete formation. gamete Mendel’s Test Using the Seed Shape Character with the Seed Color Character Character Define Alleles and Associated Traits: Seed Shape Character R = round seed trait (dominant) r = wrinkle seed trait (recessive) Mendel’s Test Using the Seed Shape Character with the Seed Color Character Character Define Alleles and Associated Traits: Seed Color Character Y = yellow seed trait (dominant) y = green seed trait (recessive) Mendel’s Test Using the Seed Shape Character with the Seed Color Character Character q Parental (P) cross: crossed truebreeding plants that produce roundyellow (RRYY) seeds with truebreeding plants that produce breeding wrinkled-green seeds (rryy). wrinkled-green Mendel’s Test Using the Seed Shape Character with the Seed Color Character Character q F1 Generation: hybrids for both characters (Rr & Yy; or RrYy) were100% round-yellow. were100% q F1 Generation Individuals (RrYy) crossed among each other. crossed Mendel’s Test Using the Seed Shape Character with the Seed Color Character Character q F2 Generation Results:  315 (56.7%) round-yellow  108 (19.4%) round-green  101 (18.2%) wrinkled-yellow  32 (5.8%) wrinkled-green No Independent Assortment Assortment With Independent Assortment Assortment Calculating Expected Frequencies Calculating Round-Yellow q Expect Expect /16 of the F2 generation offspring to be round-yellow. offspring q Therefore, of a total of 556 offspring Therefore, the expected number (frequency) of round-yellow offspring may be calculated as follows: calculated 9 9 16 Frequency = ( / )*556 = 312.75 Calculating Expected Frequencies Calculating Round-Green q Expect Expect /16 of the F2 generation offspring to be round-green. offspring q Therefore, of a total of 556 offspring Therefore, the expected number (frequency) of round-yellow offspring may be calculated as follows: calculated 3 3 16 Frequency = ( / )*556 = 104.25 Calculating Expected Frequencies Calculating Wrinkled- Yellow q Expect Expect /16 of the F2 generation offspring to be wrinkled-yellow. offspring q Therefore, of a total of 556 offspring Therefore, the expected number (frequency) of round-yellow offspring may be calculated as follows: calculated 3 3 16 Frequency = ( / )*556 = 104.25 Calculating Expected Frequencies Calculating Wrinkled- Green q Expect Expect /16 of the F2 generation offspring to be wrinkled-yellow. offspring q Therefore, of a total of 556 offspring Therefore, the expected number (frequency) of round-yellow offspring may be calculated as follows: calculated 1 1 16 Frequency = ( / )*556 = 34.75 Comparing Observed to Expected Results Results Observed Expected Round-Yellow Round-Yellow 315 312.75 Round-Green Round-Green 108 104.25 Wrinkled-Yellow Wrinkled-Yellow 101 104.25 Wrinkled-Green Wrinkled-Green 32 34.75 ...
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This note was uploaded on 04/19/2011 for the course BIOL 101 taught by Professor Wong during the Fall '09 term at University of Hawaii, Manoa.

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