Mendel & Heredity Chapter 11.1 The Origins of Genetics

Heredity The passing of traits from parents to offspring is known as heredity. The passing of traits from parents to offspring is known as heredity. What are some examples of traits that are passed from your parents? What are some examples of traits that are passed from your parents? Even before the structure of DNA was discovered people were interested in how genes on DNA were passed from generation to generation. Even before the structure of DNA was discovered people were interested in how genes on DNA were passed from generation to generation.

Gregor Mendel Gregor Mendel was an Austrian monk born in Gregor Mendel was an Austrian monk born in Mendel is known today as the father of modern genetics. Mendel is known today as the father of modern genetics. Mendel performed experiments on different varieties of pea plants. Mendel performed experiments on different varieties of pea plants. Mendel used pea plants because there are many different traits, they grew quickly and they can self-pollinate. Mendel used pea plants because there are many different traits, they grew quickly and they can self-pollinate.

Seven traits Mendel studied Flower color – (purple & white) Flower color – (purple & white) Seed color – (yellow & green) Seed color – (yellow & green) Seed shape – (round & wrinkled) Seed shape – (round & wrinkled) Pod color – (green & yellow) Pod color – (green & yellow) Pod shape – (smooth & wrinkled) Pod shape – (smooth & wrinkled) Flower position – (middle & top) Flower position – (middle & top) Plant height – (tall & short) Plant height – (tall & short)

Mendel’s Observation Mendel’s first observation came from a monohybrid cross a cross that involves one pair of contrasting traits. Mendel’s first observation came from a monohybrid cross a cross that involves one pair of contrasting traits. For example crossing a plant with purple flowers with one with white flowers. For example crossing a plant with purple flowers with one with white flowers. In order to make sure he had true- breeding purple & white plants Mendel self-pollinated each for many generations. In order to make sure he had true- breeding purple & white plants Mendel self-pollinated each for many generations.

Three Steps of Mendel’s Experiments. Step 1: Mendel crossed the two different true-breeding plants & called it the P (or parental) generation. Step 1: Mendel crossed the two different true-breeding plants & called it the P (or parental) generation. Step 2: The offspring from the P generation were then crossed and called the F 1 Generation. Step 2: The offspring from the P generation were then crossed and called the F 1 Generation. Step 3: The offspring from the F 1 generation were then crossed and called the F 2 Generation. Step 3: The offspring from the F 1 generation were then crossed and called the F 2 Generation.

Mendels Results After the P generation was crossed Mendel noticed that all of the offspring exhibited one type of color, the other color “disappeared”. After the P generation was crossed Mendel noticed that all of the offspring exhibited one type of color, the other color “disappeared”. In the F 2 generation the color that “disappeared” came back in a ratio of about one in every four. In the F 2 generation the color that “disappeared” came back in a ratio of about one in every four.

Calculating Mendel’s ratios. Mendel noticed that he had 705 purple flowers and 224 white flowers in his F 2 generation. Mendel noticed that he had 705 purple flowers and 224 white flowers in his F 2 generation. 705/224 = /224 = /224 = 1 224/224 = 1 A ratio of about 3:1 A ratio of about 3:1 Do your own: 787 tall plants & 277 short. Do your own: 787 tall plants & 277 short.

Review Questions Why did Mendel use pea plants? Why did Mendel use pea plants? What was the ratio Mendel noticed in his F 2 generation? What was the ratio Mendel noticed in his F 2 generation? What is the following ratio of pod color 428 green & 152 yellow. What is the following ratio of pod color 428 green & 152 yellow. How did Mendel make sure that his P generation were true-breeding? How did Mendel make sure that his P generation were true-breeding?