1. Mendel’s Law of Segregation
Pre-AP Biology

2. Bellwork
How are Punnett Squares related to Meiosis?

3. Objectives Explain Mendel’s contribution to genetics
Describe why garden peas are a good model organism for studying genetics
State Mendel’s law of segregation
Explain the relationship between Mendel’s law of segregation and meiosis

4. Key Terminology Blending Theory Self-fertilizaton Cross-fertilization
P Generation
F1 generation
F2 generation
Law of segregation

5. Pre-Mendelian Theory of Heredity
Blending theory – Hereditary material from each parent blends in the offspring;
once blended traits inseparable
After many generations, the individuals of the population will reach a uniform appearance.

6. Gregor Mendel Austrian Monk Worked with garden peas
Known as the Father of Genetics
Developed the two laws of inheritance
Law of Segregation
Law of Independent Assortment

7. Why garden peas?
Considered a model organism for studying genetics. Why?
Strict control over mating.
Flowers contain both male and female reproductive organs.
Allow:
Self fertilization – pollen fertilizes egg from same flower.
Cross- pollination – pollen fertilizes egg from flower of different plant.

8. Why garden peas?
Short life cycle
Grow several generations in a year

9. Think-Pair -Share
Explain the difference between self-fertilization and cross-fertilization, IYOW

10. Why garden peas? (Cont’d)
Could detect heritable traits.
Have many traits to examine.
Examples of those traits:
Flower color (purple vs. white)
Seed color (yellow vs. green)
Seed shape (round vs. wrinkled)
Stem length (tall vs. dwarf)

11. Think-Pair-Share
Explain why garden peas were a good model organism for studying Genetics? Why were humans not chosen?

12. Mendel’s First Experiment
Hypothesis: If blending theory true
Experimental Design
Cross plants with purple flowers (PP) and plants with white flowers (pp)
Predicted Result
Offspring will have flowers of an intermediate color
Color will remain for remaining generations

13. Mendel’s First Experiment (Cont’d)
Crossed purple with white flowering plants.
F1 generation:
all purple flowers
Selfed the F1 generation
F2 generation :
3:1 ratio of purple to white flowers

14. Mendel’s Conclusions
Traits do not blend because F2 showed parent’s original traits
Each parent has two separate genes for a particular trait.
During gamete formation (meiosis), the two genes on the respective homologues separate.
Mendel’s first law of inheritance
the law of segregation

15. Mendel’s Conclusions
During fertilization, each offspring receives one version of each gene (allele) from each parent

16. Paraphrase IYOW
Summarize the Law of Segregation IYOW and explain how it is related to meiosis