2. Chapter 5 section 1

3. What is heredity ?

4. Heredity is… the passing of traits from parents to offspring.

5. Who first studied heredity?

6.  born in 1822  Served as a monk (a type of religious life)  Known as the “father of genetics”

7. Worked as  A Gardener in a monastery  Experimented with pea plants to understand the process of heredity heredity

8. Unraveling a Mystery  Mendel was interested in how traits (physical characteristics) were passed down from parents to offspring  He saw that sometimes a trait would show up in one generation but not the next.  He decided to study these patterns in pea plants.

9. Used pea plants  Grow quickly and have a fast life cycle (from seed to offspring)  Could self-pollinate and cross-pollinate

10. Pea Plants  Come in many varieties (round vs. wrinkled seed, purple vs. white flowers)  Each characteristic had 2 forms

11. Mendel’s Experiments  Cross-pollinated plants with contrasting traits. (Ex: tall plant x short plant)  Had to start with two purebred plants (true-breeding) plants – plants that are the result of many generations of the same trait. (Example: purebred short plants always come from short parent plants)

12. Mendel’s Experiments  Had to control cross-pollination:  Anthers of flower are removed from one plant.  Pollen from another plant with contrasting trait is used to fertilize the plant with no anthers

13. Mendel’s 1 st Experiment  Mendel crossed two purebred plants with one contrasting trait. This was the parental generation (P generation)  Example: purebred tall plant x purebred short plant  Result: All offspring were tall. (F 1 generation)

14. X Parent Tall P generation Parent Short P generation All Offspring Tall F 1 generation

15. Conclusion  There are two forms of each trait. One is dominant the other recessive.  Dominant trait – the trait that was present in the F 1 generation.

16. Conclusion  Recessive trait - the trait that seemed to disappear  Mendel performed a second experiment to find out what happened to this trait

17. Mendel’s 2 nd Experiment  Mendel allowed the F 1 generation to self- pollinate.  Result: ¾ of the offspring were tall, ¼ were short (F 2 generation)  The recessive trait reappeared in the F 2 generation.  Always occurred in the above ratio, didn’t matter what trait it was (plant height, flower color, seed shape, etc…)

18. . Tall F1 generation X 3⁄4 Tall & 1⁄4 Short F2 generation Parent PlantsOffspring

19. Mendel’s Conclusion  Each parent donates one set of instructions to the offspring.  These instructions are now known as GENES

20. What are genes?  Sections of DNA  Genes are represented by a letter  Sometimes, one gene controls a trait

21. Genes Have Two Forms  There are two forms of each gene - called alleles.  Organisms inherit one allele from each parent  Some alleles are dominant over others. The dominant allele “masks” the presence of the recessive allele.  If the recessive form of the trait shows, then the organism must have 2 recessive alleles.

22. Alleles  Dominant alleles are symbolized with capital letters (T, B, X, C)  Recessive alleles are symbolized with lowercase letters (t, b, x c)  An organism can be purebred dominant (TT), purebred recessive (tt), or hybrid (Tt) for a trait  A hybrid individual will show the dominant trait.

23. Genes and Mendel’s Experiments  Parent Generation: tall x short TT x tt TT x tt  F 1 Generation: All hybrids All Tt = All Tall All Tt = All Tall  F 2 Generation:  ¾ inherited at least 1 dominant allele (T) = Tall  ¼ inherited 2 recessive alleles (t) = short

24. X Tall parent TT Short parent tt All Offspring Tall F 1 generation Tt Mendel’s 1 st experiment: Tall is dominant, short recessive Mendel’s 2 nd experiment: Tall is dominant, short recessive X Tall F 1 generation Tt F 2 generation ¾ TT or Tt and ¼ tt