Introduction:
Gregor Mendel was an Austrian monk who lived and worked in the mid nineteenth century. Mendel grew up on a farm and was very interested in heredity.
Mendel was curious about how living things get their characteristics or traits. Why do some individuals look more like their mother, and others more like their father, or even a grandparent? In order to solve this puzzle Mendel studied pea plants. He looked at 7 different traits, each one with two variants. A trait is a characteristic that a living thing has, like size, color, texture. A variant is the different forms that a trait can have. For example, in pea plants
Trait: height
Variants: tall or short
Name a trait and its variants that you would find in humans
Trait:
Variants:
Based on what we learned earlier in this unit, what causes different variants for a trait?
Mendel chose traits that only had two variants, but keep in mind that many traits have more than two variants.
For this activity you will be given a selection of Mendel’s data and it will be your task to solve the puzzle of heredity, just as Mendel did!
Crossing the Peas!
Mendel started with a pure strain for each of his variants. A pure strain is a group of critters that always produce the same variant generation after generation. For his first cross Mendel used pure strains of the two variants for each trait. In this activity we will just be looking at one trait, seed color. Peas can be green or yellow.
Parental Generation (P generation)
20 green x 20 yellow
Go to the counter and look at the F1 generation.
The next generation is called the first filial generation, symbolized F1. Go to the front counter and look at this generation.
Phenotype of F1 generation _______________
So, what happened to the information for being green? (Mendel called this piece of information a factor) Here are two possible hypotheses. a) The information (factor) was not passed on from offspring to child. b) The information (factor) was passed on, but not expressed (remains hidden).
Which hypothesis, or both, is supported by the data so far?
Which hypothesis makes the most sense based on what you have learned about meiosis? Explain
If hypothesis (a) is correct then what would you expect the next generation to look like?
If hypothesis (b) is correct then what would you expect the next generation to look like?
For the next cross we will mate members of the F1 generation with each other. This will produce the second filial generation, or F2 generation. Obtain a sample of the
F2 generation from your teacher. Count the number of green and yellow peas in the
F2 generation.
F2 Generation
Yellow ___________
Green ___________
We now need to put this data in a more understandable form, by determining the phenotypic ratio.
To find the phenotypic ratio divide the number of yellow peas by the number of green peas and round to the nearest whole number. You now have some number over 1. This is your phenotypic ratio. It can also be written in side by side form.
(___ : ___). Determine your phenotypic ratio using the guides below.
Yellow = _______ = ______
Green 1
Yellow: Green
( _____ : _____)
Which hypothesis is supported by the data now?
Explain your reasoning.

Pulling it all together
1. Based on this experiment, how many copies of genetic information (factors) does each pea have for each trait?
2. How many of these factors are expressed (show in the plant)?
The pattern you have just discovered Mendel called the principle of dominance and recessiveness.
3. State this principle in your own words:
4. So, if all living things have two factors (copies of information) for every trait then where do you think a living thing gets these factors from?
5. How many factors for each trait must each parent pass on to one offspring?
Explain how you know.
6. This idea Mendel named the principle of segregation. Restate this in your own words:
7. What do we call Mendel’s factors now?
Pulling it all together
1. Based on this experiment, how many copies of genetic information (factors) does each pea have for each trait?
2. How many of these factors are expressed (show in the plant)?
The pattern you have just discovered Mendel called the principle of dominance and recessiveness.
3. State this principle in your own words:
4. So, if all living things have two factors (copies of information) for every trait then where do you think a living thing gets these factors from?
5. How many factors for each trait must each parent pass on to one offspring?
Explain how you know.
6. This idea Mendel named the principle of segregation. Restate this in your own words:
7. What do we call Mendel’s factors now?