Unit 1: Mendel's Principles of Inheritance

The Blending Hypothesis

* Most widely accepted explanation of heredity in the 1800s
* Genetic material contributed by both parents blended together
* Would give rise to uniform population if free mating

The Particulate Approach

* Parents pass on discrete heritable units (genes) that retain their separate identities in their offspring

What type of plant did Mendel study? Why were they a good choice?

Peas. There are many varieties, short generation time, easy to control mating, easy to get large sample size.

How did Mendel control the breeding of the pea plants?

He removed immature stamen from a plant before they produced pollen and then dusted flowers with pollen from a separate plant with a paint brush.

Character Definition

A heritable feature that varies among individuals such as eye colour. The physical manifestation of a trait.

Trait Definition

Each variant/option for a character like brown, blue, or green eyes.

For what two reasons did Mendel’s experiment work?

1. Because the specific plants only had one gene controlling the characters he was observing.
2. Because he only used plants that were true-breeding.

True-Breeding Definition

Displaying the same traits over several generations, either all dominant or all recessive.

Hybridization Definition

Cross breeding two true-breeding plants that express different traits for the same character.

Generational Order

P Generation = Parental Generation

F1 Generation = First Filial/First Sons

F2 Generation = Second Filial/Second Sons

Mendel’s Experiment Process

* Cross two true-breeding parents (white and purple)
* Creates all purple flowers in F1
* Cross two purple flowers in F1 to create F2
* F2 ratio is 3 purples:1 white continuously, which disproves the blending hypothesis
* He also carried these observations out through different characters like flower position, seed colour, seed shape, pod shape, pod colour, and stem length and got the same 3:1 ratio as a result

What are Mendel’s two fundamental principles of heredity?

1) The Law of Segregation

2) The Law of Independent Assortment

For what 2 reasons could Mendel be sure that any offspring produced by the pea plants were by his design?

1) He started with true-breeds.

2) He sterilized the plants so there was no natural reproduction.

Mendel’s Law of Segregation

States that complementary alleles separate during gamete formation and randomly unite at fertilization (random joining of segregated alleles).

Mendel’s Law of Independent Assortment

States that the alleles of two (or more) different genes get sorted into gametes independently of one another.