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Chapter 11 Introduction To Genetics Section 11-3 Exploring Mendelian Genetics FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Gregor Mendel Wanted To Know If: Segregation Was Truly Independent or Does The Segregation Of One Pair Of Alleles Affect The Segregation Of Another Pair Of Alleles???? FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Independent Assortment Mendel Performed A Two Factor Cross – He Crossed Round/Yellow – With Wrinkled/Green RRYY rryy This Provided The F1 Hybrids That He Needed. FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Independent Assortment F1 Hybrid RrYy FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Independent Assortment 9:3:3:1 FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Two Factor Cross F2 All F1 Plants Were Heterozygous or Hybrid In The F2 Cross Would 1. The Dominant Alleles Stay Together 2. Or Would They Segregate Independently So Any Combination Of Alleles Would Be Possible?????? FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Two Factor Cross F2 Results 556 Seeds Produced 315 Round/Yellow F1 Parental Phenotypes 32 Wrinkled/Green Plus 209 Unique Phenotypes Can Only Form Via Independent 9:3:3:1 Assortment FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Two Factor Cross F2 Results The Alleles For Seed Shape And Color Segregated Independently INDEPENDENT ASSORTMENT did occur. Therefore These Alleles DO NOT Influence Each Others Inheritance FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Key Concept The Principle Of Independent Assortment States That Genes For Different Traits Can Segregate Independently During The Formation Of Gametes. FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Summary of Mendel’s Principles 1. Inheritance of Biological Characteristics Is Determined By Individual Units Known As Genes. In Organisms That Reproduce Sexually, Genes Are Passed From Parents To Their Offspring. FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Summary of Mendel’s Principles 2. Where Two or More Forms Of The Alleles Exist, Some Forms Of The Allele Many Be Dominant And Others May Be Recessive. FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Summary of Mendel’s Principles 3. In Most Sexually Reproducing Organisms, Each Adult Has Two Alleles In Each Gene – One From Each Parent 4. These Alleles Are Segregated From Each Other When Gametes Are Formed. FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Summary of Mendel’s Principles 5. Alleles Contained In Different Genes Usually Segregate Independently Of One Another FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Beyond Dominant & Recessive Alleles Key Concept: Some Alleles Are Neither Dominant Nor Recessive, And Many Traits Are Controlled By Multiple Alleles or Genes. FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Incomplete Dominance Red Flower Crossed With White Flower Results In Pink Flower. In Incomplete Dominance The Heterozygous Phenotype Is Between The Homozygous Phenotypes. (Both Alleles Expressed In One Cell) FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Codominance • Both Alleles Completely Expressed Red Hair Cattle Crossed With White Haired Cattle Produce Roan (Pink Brown) Cattle That Have Both Colored Hairs. (Both Alleles Expressed Independently) FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Codominance RED WHITE ROAN FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Multiple Alleles • A Gene Is Controlled By >2 Alleles. – Individuals Can Only Have 2 Alleles – Populations Can Have More Than Two • Rabbit Fur Color • Blood Types • Eye Color FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Multiple Alleles FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Multiple Alleles FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Multiple Alleles FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Polygenic Traits • Phenotypes Produced By The Interaction Of Several Genes. – Human Skin Color Is Controlled By More Than 4 Different Genes. – Eye Color is Controlled By At Least 3 Genes FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Applying Mendel’s Principles Thomas Hunt Morgan – early 1900’s – Drosophila melanogaster • Easy To Raise • Produces Numerous Offspring Every 14 Days • Large Chromosomes • Susceptible To Mutagens FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT