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Introduction to Genetics. Chapter 11. The Work of Gregor Mendel. Section 11.1. Genetics. Scientific study of heredity Every living thing has a set of characteristics inherited from its parent(s) Heredity helps with the understanding of what makes each species unique.
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Introduction to Genetics Chapter 11
The Work of Gregor Mendel Section 11.1
Genetics • Scientific study of heredity • Every living thing has a set of characteristics inherited from its parent(s) • Heredity helps with the understanding of what makes each species unique
Gregor Mendel’s Peas • Austrian monk who worked with garden peas • Male part of each flower produces pollen • Male sex cells • Female part of each flower produces eggs • Female sex cells • When pollen fertilizes an egg, a seed for a new plant is formed • Pea plants normally self-pollinate • Pollen fertilizes the egg cells in the very same flower • Seeds that are produced by self-pollination inherit all of their characteristics from the single plant • They have only 1 parent • Mendel’s pea plants started out to be true-breeding • When they self pollinate they produce offspring identical to themselves • Pea plants can cross pollinate • Male sex cells in pollen from the flower on one plant fertilizes the egg cells of a flower on another plant • Seeds produced from cross pollination have 2 parents
Mendel’s Experiment • Mendel selected pea plants that he would prevent from self-pollinating • He wanted the plants to cross pollinate • He cut away the male parts of a flower • He dusted the flower with pollen from a second flower • The resulting seeds were crosses between the 2 plants • Several traits were studied • Specific characteristics such as seed color or plant height • He studied 7 different traits • The original pair he called the P generation (parent) • He called the offspring the F1 or the “First Filial” generation • The offspring of the crosses between parents with different traits are called hybrids
Mendel’s Findings • All of the offspring had the character of only 1 of the parents • Biological inheritance is determined by factors that are passed from one generation to the next • These chemical factors that determine traits are called genes • Each trait was controlled by one gene that occurredin 2 contrasting forms called alleles • These contrasting forms produced the different characters of each trait • Principle of dominance
Principle of Dominance • Some alleles are dominant and others are recessive • Organisms with a dominant allele for a particular form of a trait will always have that form • An organism with a recessive allele for a particular form of a trait will have that form only when the dominant allele for the trait is not present
Probability and Punnett Squares Section 11.2
Probability • The likelihood that a particular event will occur • Independent events • Past outcomes do not affect future ones • Multiply the individual probabilities • The way alleles segregate is completely random which means that the principles of probability can be used to predict the outcomes of genetic crosses
Punnett Squares r r • Gene combination that might result from a genetic cross can be determined by completing • Types of gametes of parents are located across the top and down side • Possible gene and combinations for the offspring will appear in the four boxes • Letters represent the alleles • Capital is dominant and lowercase is the recessive allele Rr Rr R r rr rr ^^Probability of offspring for a red heterozygous rose crossed with a pink recessive rose.
Traits • 2 identical alleles for a particular trait • RR • rr • True-breeding for a particular trait • 2 different alleles for the same trait • Rr • Hybrid for a particular trait Homozygous Heterozygous
Characteristics • Phenotype • Physical Characteristics • Tall/short • Genotype • Genetic makeup • RR, Rr, rr
Probabilities • Predict the average outcome of a large number of events • Cannot predict the precise outcome of individual events • The larger number of individuals, the closer the resulting offspring number will get to expected values
Exploring Mendelian Genetics Section 11.3
Two-Factor Cross • When crossing 2 true-breeding (RRYY X rryy) all of the offspring will be completely heterzygous • When crossing 2 plants from F1 generation (RrYy X RrYy) the genotype of the parents did not show up this meant that the alleles for seed shape segregated independently of those for seed color • Independent assortment • The phenotype will always be 9:3:3:1 F1 F2
