Mendel’s Law of Segregation Pre-AP Biology

Bellwork How are Punnett Squares related to Meiosis?

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

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

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.

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

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.

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

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

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)

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

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

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

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

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

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