Understanding Mendel's Principles of Genetics: Dominance and Heredity

1. Chapter 11Introduction to GeneticsP. 64

2. X First Generation (F1) X 100% pink!!! Second Generation (F2) How did this happen? 3 pink, 1 blue - ¾ pink(75%), ¼ blue (25%)

3. Genetics!!! Section 11-1 • 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 heredityand its importance in biology

4. 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.

5. 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 theparent 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

6. Mendel’s Experiment P generation tall short

7. Mendel’s Experiment F1 generation P generation tall short tall tall

8. Mendel’s Results All the F1 plants expressed only the dominant trait! Seed Shape Seed Color Seed Coat Color PodShape PodColor FlowerPosition FlowerHeight wrinkled green white constricted yellow terminal short Yellow dominant Smooth dominant Axial dominant Tall dominant round yellow gray smooth green tall axial Round dominant Gray dominant Green dominant

9. Mendel’s Principles of Heredity Hello! • Mendel learned 2 principles from these experiments: • Biological inheritance is determined by factors (we call them genes) that are passed from one generation to the next, Genes = chemical factors that determine traits – each trait is controlled by 1 genethat occurs in 2 contrasting formsor alleles Allele = a different form of a gene • 2. Principle of Dominance: some alleles are dominant and others are recessive

10. 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!

11. 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 self-pollinate F1 XF1 F2

12. Mendel’s Experiment F1 generation P generation tall short tall tall

13. Mendel’s Experiment F1 generation F2 generation P generation tall short tall tall tall tall tall short

14. F1 Cross • Mendel thought the results for his F1 cross were amazing! • All the recessive traits re-appeared in the F2 offspring!