Mendel & HeredityMendel & Heredity

Chapter 11.1Chapter 11.1

The Origins of GeneticsThe Origins of Genetics

HeredityHeredity

The passing of traits from parents to The passing of traits from parents to offspring is known as offspring is known as heredityheredity..

What are some examples of traits What are some examples of traits that are passed from your parents?that are passed from your parents?

Even before the structure of DNA was Even before the structure of DNA was discovered people were interested in discovered people were interested in how genes on DNA were passed from how genes on DNA were passed from generation to generation.generation to generation.

Gregor MendelGregor Mendel Gregor Mendel was an Austrian monk Gregor Mendel was an Austrian monk

born in 1822.born in 1822. Mendel is known today as the father of Mendel is known today as the father of

modern genetics.modern genetics. Mendel performed experiments on Mendel performed experiments on

different varieties of pea plants.different varieties of pea plants. Mendel used pea plants because there Mendel used pea plants because there

are many different traits, they grew are many different traits, they grew quickly and they can self-pollinate.quickly and they can self-pollinate.

Seven traits Mendel Seven traits Mendel studiedstudied 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 ObservationMendel’s Observation

Mendel’s first observation came from a Mendel’s first observation came from a monohybrid crossmonohybrid cross a cross that involves a cross that involves one pair of contrasting traits.one pair of contrasting traits.

For example crossing a plant with For example crossing a plant with purple flowers with one with white purple flowers with one with white flowers.flowers.

In order to make sure he had true-In order to make sure he had true-breeding purple & white plants Mendel breeding purple & white plants Mendel self-pollinated each for many self-pollinated each for many generations.generations.

Three Steps of Three Steps of Mendel’s Experiments.Mendel’s Experiments. Step 1: Mendel crossed the two Step 1: Mendel crossed the two

different true-breeding plants & different true-breeding plants & called it the P (or parental) called it the P (or parental) generation.generation.

Step 2: The offspring from the P Step 2: The offspring from the P generation were then crossed and generation were then crossed and called the Fcalled the F11 Generation. Generation.

Step 3: The offspring from the FStep 3: The offspring from the F11 generation were then crossed and generation were then crossed and called the Fcalled the F22 Generation. Generation.

Mendels ResultsMendels Results

After the P generation was After the P generation was crossed Mendel noticed that all of crossed Mendel noticed that all of the offspring exhibited one type the offspring exhibited one type of color, the other color of color, the other color “disappeared”.“disappeared”.

In the FIn the F22 generation the color that generation the color that “disappeared” came back in a “disappeared” came back in a ratio of about one in every four. ratio of about one in every four.

Calculating Mendel’s Calculating Mendel’s ratios.ratios. Mendel noticed that he had 705 Mendel noticed that he had 705

purple flowers and 224 white flowers purple flowers and 224 white flowers in his Fin his F22 generation. generation.

705/224 = 3.15705/224 = 3.15 224/224 = 1224/224 = 1 A ratio of about 3:1A ratio of about 3:1 Do your own: 787 tall plants & 277 Do your own: 787 tall plants & 277

short.short.

Review QuestionsReview Questions

Why did Mendel use pea plants?Why did Mendel use pea plants? What was the ratio Mendel noticed What was the ratio Mendel noticed

in his Fin his F22 generation? generation? What is the following ratio of pod What is the following ratio of pod

color 428 green & 152 yellow.color 428 green & 152 yellow. How did Mendel make sure that his How did Mendel make sure that his

P generation were true-breeding?P generation were true-breeding?