# Chapter 14 Part I: Mendel and the Gene Idea This chapter details Mendel’s discovery of general laws of heredity as well as monohybrid dihybrid genetic.

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Chapter 14 Part I: Mendel and the Gene Idea This chapter details Mendel’s discovery of general laws of heredity as well as monohybrid dihybrid genetic crosses.

A. Gregor Mendel 1Austrian Monk 2Formulated two laws of inheritance in 1860s. 3Previously studied math and science at University of Vienna.

B. Blending Concepts of Inheritance 1Theory stated that offspring would possess traits intermediate between those of different parents. 2Red and White flowers make Pink flowers. 3Darwin wanted to develop a theory of evolution based on Mendel’s heredity principles.

C. Mendel’s Experimental Procedure 1Mendel did a statistical study 2Prepared experiments carefully A. Garden Pea B. 22 true-breeding varieties C. Simple traits were studied 3Mendel traced inheritance of individual traits. 4Principles of probability used for interpretation.

11.2 Monohybrid Inheritance A. Cross-pollination Monohybrid Crosses 1A hybrid is result of 2 true-breeding parents 2A monohybrid cross is between two true-breeding parents for two distinct forms of a trait. 3Mendel tracked 2 generations A. P Generation B. F1 Generation C. F2 Generation

B. Mendel’s Results 1Contrary results to predictions 2F1 resembled one parent 31/4 of F2 resembled one parent; 3/4 resembled other parent like F1 generation. 43:1 ratio results A. Dominant/recessive shown in F2. B. Factors separated when gametes were formed. C. Random fusion upon fertilization.

B. Mendel’s Results Continued 5Mendel’s First Law of Inheritance: Law of Segregation A. Each organism contains 2 factors for each trait; factors segregate in formation of gametes; each gamete contains one factor for each trait. B. Factors passed from generation to generation

C. As Viewed by Modern Genetics 1Traits controlled by two alleles, alternate forms of trait found at the same gene locus. 2Gene locus is a specific location on a gene 3Homozygous is two identical alleles for a trait. A. Homozygous dominant - 2 dominant alleles B. Homozygous recessive - 2 recessive alleles 4After cross-pollination, all F1 are heterozygous genotypes.

D. Genotype Vs. Phenotype 12 organisms with different allele combinations can have same outward appearance (TT & Tt) 2Genotype refers to alleles at fertilization. 3Phenotype refers to physical appearance.

E. Laws of Probability 1Probability is the likely outcome a given event will occur from random chance. 2Multiplicative law of probability = chance of 2 or more independent events occurring together is the product of the probability of the events occurring separately 3Additive law of probability = probability of an event that occurs in 2 or more independent ways.

F. The Punnet Square 1Provides simple method to calculate probable results of genetic cross. 2Sperm cells lined up vertically; egg cells lined up horizontally. 3Larger sample sizes give better outcomes for predicted ratios. 4Humans use phenotypic rations for predictions.

G. One-Trait Testcross 1Mendel performed testcrosses by crossing F1 to homozygous recessive. 2Results indicated recessive factor in F1. 3Testcross = dominant phenotypic individual crossed with recessive individual.

11.3 Dihybrid Inheritance A. Dihybrid Crosses 1Dihybrid cross is an experimental cross between 2 true-breeding parents for 2 different traits. B. Plants Self-Pollinate 1Mendel observed 4 phenotypes among F2. 2This gave him Second Law of Heredity: law of independent assortment. A. Members assort independently of each other.

C. Dihybrid Genetics Problems 1Laws of probability indicate a 9:3:3:1 phenotypic ratio of F2. A. 9/16 dominant for both traits B. 3/16 dominant for 1 trait, recessive for other C. 3/16 dominant/recessive opposite of previous D. 1/16 recessive for both traits 29:3:3:1 ratio expected when heterozygous for 2 traits are crossed.

D. Two-Trait Test Cross 1Dihybrid Test Cross - homozygous dominant traits or heterozygous. 2Dihybrid genetic problems: 4 alleles for 2 traits. END OF CHAPTER 11

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