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Transcript
Genetics Gregor Mendel Pea Plant Experiment • Gregor Mendel chose pea plants to conduct genetic experiments because of their plant life special properties. • For example: – When pollen fertilizes an egg cell, a seed for a new plant is formed. – Pea plants normally reproduce by self-pollination. – This is asexual reproduction Gregor Mendel Pea Plant Experiment • Plants contain both female and male organs • What does it mean when pea plants are described as being true-breeding? • If the plants are allowed to self-pollinate, they would produce offspring identical to themselves. Gregor Mendel Pea Plant Experiment • To perform his experiments, how did Mendel controlled cross-pollination and prevented self-pollinating • He cut away the pollen-bearing male parts of a flower and dusted that flower with pollen from another plant. Gregor Mendel Pea Plant Experiment • Traits - Specific characteristics that vary from one individual to another • Hybrids-The offspring of crosses between parents with different traits • Genes - Chemical factors that determine traits • Alleles - The different forms of a gene • Genetics – Scientific study of heredity • Gametes – sex cells Alleles • Can be dominant of recessive “traits” • An organism with a recessive allele for a particular form of a trait will NOT always exhibit that form. Characteristics of Traits • How did Mendel allowed the F1 (Generation 1) plants to produce an F2 (Generation 2) generation by self-pollination. • Mendel noted that a dominant allele had masked the corresponding recessive allele in the F1 generation. Characteristics of Traits • At some point, the allele for shortness was segregated, or separated, from the allele for tallness. In the diagram above, the dominant allele is represented by T and the recessive allele is represented by t . Probability and Punnett Squares Assignment 1. Who is the “Father of Genetics”? 2. What did he use to experiment upon? 3. What is the difference between selfpollination and cross-pollination? 4. What is asexual reproduction? 5. What allows plants to self-pollinate? 6. How did Mendel prove that the recessive gene was being masked by the dominant gene? Probability The likelihood that a particular event will occur is called_______. • Probability Probability Circle the letter of the probability that a single coin flip will come up heads. • a. 100 percent • b. 75 percent • c. 50 percent • d. 25 percent Probability • Is the following sentence true or false? • The past outcomes of coin flips greatly affect the outcomes of future coin flips. • False Probability • Why can the principles of probability be used to predict the outcomes of genetic crosses? • The way in which the alleles segregate is completely random, like a coin flip. Punnett Squares • How do geneticists use Punnett squares? • Punnett squares can be used to predict and compare the genetic variations that will result from a cross. Punnett Square Complete the Punnett square to show the possible gene combinations for the F2 offspring. Allele Types • • • • Homo - Same Hetero - Opposite Pheno – Physical Geno - Genetic Allele Types Definitions • Organisms that have two identical alleles • particular trait (TT or tt) Homozygous • Organisms that have two different alleles • same trait (Tt) Heterozygous • Physical characteristic of an organism Phenotype • Genetic makeup of an organism (Tt) Genotype Gene Expression Are the following sentences true or false? - Homozygous organisms are true breeding for a particular trait. • False - Plants with the same phenotype always have the same genotype. • False Probability and Segregation • b. The F2 ratio of tall plants to short plants produced in a cross between two hybrid tall pea plants (Tt) is 3 tall plants for every 1 short plant. • c. Mendel observed that about 3⁄4 of the F2 offspring showed the dominant trait. • d. Segregation occurs according to Mendel’s model. Probability • In Mendel’s model of segregation, what was the ratio of tall plants to short plants in the F2 generation? • The ratio was 3 : 1. Probability • Is the following sentence true or false? • Probabilities predict the precise outcome of an individual event. • False Probability • How can you be sure of getting the expected 50 : 50 ratio from flipping a coin? • You must flip the coin many times. Probability 17. The _____ number of offspring from a genetic cross, the closer the resulting numbers will get to expected values. • Larger Probability Is the following sentence true or false? • The ratios of an F1 generation are more likely to match Mendelian predicted ratios if the F1 generation contains hundreds or thousands of individuals. • True Exploring Mendelian Genetics • Section 11–3 Independent Assortment • In a two-factor cross, Mendel followed______ different genes as they passed from one generation to the next. • 2 Independent Assortment • Write the genotypes of the true-breeding plants that Mendel used in his two-factor cross. • Phenotype Genotype a. round yellow peas __RRYY_ b. wrinkled green peas __rryy_ Independent Assortment • Heterozygous dominant with round yellow peas, best describes the F1 offspring of Mendel’s two-factor cross. Independent Assortment • Is the following sentence true or false? • The genotypes of the F1 offspring indicated to Mendel that genes assort independently. • False Independent Assortment How did Mendel produce the F2 offspring? • He crossed F1 plants to each other. Independent Assortment • Circle the letter of the phenotypes that Mendel would expect to see if genes segregated independently. • a. round and yellow • b. wrinkled and green • c. round and green • d. wrinkled and yellow • What did Mendel observe in the F2 offspring that showed him that the alleles for seed • shape segregate independently of those for seed color? He observed F2 offspring that had • combinations of phenotypes—and therefore combinations of alleles—not found in either parent.