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Chapter 11 Introduction to Genetics P. 64 X First Generation (F1) X 100% pink!!! Second Generation (F2) 3 pink, 1 blue - ¾ pink (75%), ¼ blue (25%) How did this happen? Section 11-1 Genetics!!! • Patterns of Inheritance • You inherit traits (physical characteristics) from your parents- Heredity! • Heredity is what makes you unique – Examples of Traits: • Blue, Green, Brown, Black, Hazel Eye color • Genetics = the scientific study of heredity and its importance in biology Gregor Mendel • Gregor Mendel (1822), an Austrian monk who studied inheritance patterns in pea plants, his work is now considered the foundation of modern genetics – He worked with ordinary garden peas, planted in the garden at his monastery. What Mendel Found • Mendel studied 7 different pea plant traits that varied from one individual plant to the next (like human traits!) • These traits had 2 forms, such as either green seeds or yellow seeds, smooth pods or wrinkled pods – He crossed plants with each of the 7 contrasting characteristics and studied their offspring • P = represents the parent generation • F (from the Latin word fillius and filia- son and daughter) are the offspring • F1 = first generation • F2 = second generation • Hybrids = offspring of crosses between parents with different traits Mendel’s Experiment P generation tall short Mendel’s Experiment P generation tall short F1 generation tall tall Mendel’s Results All the F1 plants expressed only the dominant trait! Seed Shape Seed Color Seed Coat Color Pod Shape wrinkled green white constricted Yellow dominant Pod Color Flower Position Flower Height yellow terminal short Smooth dominant Axial dominant Tall dominant round Round dominant yellow gray Gray dominant smooth green Green dominant axial tall Mendel’s Principles of Heredity • Hello! Mendel learned 2 principles from these experiments: 1. Biological inheritance is determined by factors (we call them genes) that are passed from one generation to the next, Allele = a Genes = chemical factors that different form of a gene determine traits – each trait is controlled by 1 gene that occurs in 2 contrasting forms or alleles 2. Principle of Dominance: some alleles are dominant and others are recessive Principle of Dominance • An organism with a dominant allele for a particular form of a trait will always exhibit that form of the trait • In other words, if you have the dominant allele, you will express that dominant trait • An organism with a recessive allele for a particular form of a trait will exhibit that form only when the dominant allele is not present • In other words, you must have 2 recessive alleles to express the recessive trait I’m Dominant!! Tall = TT or Tt Short = tt Eeek! Where did the recessive traits go? • Mendel wanted to know why all his F1 plants expressed only dominant traits ????? • He wondered, “Had all the recessive traits disappeared? Or were they still present in the F1 plants?” • To answer this question, he allowed his F1 plants to selfpollinate F1 X F1 F2 Mendel’s Experiment P generation tall short F1 generation tall tall Mendel’s Experiment P generation tall short F1 generation tall tall F2 generation tall tall tall short F1 Cross • Mendel thought the results for his F1 cross were amazing! • All the recessive traits reappeared in the F2 offspring!
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