lecture 2.01: mendel's study - scottsdale community college

Inheritance and genetics Mendel’s study

Lecture 2.01: Mendel’s Study

John D. Nagy

Scottsdale Community College

BIO 181, General Biology for Majors

John Nagy Lec 2.01: Mendel’s Study

Inheritance and genetics Mendel’s study

Outline

1 Inheritance and geneticsBasic concepts19th Century theory

2 Mendel’s studyMethodsInitial results


Inheritance and genetics Mendel’s study Basic concepts 19th Century theory

The importance of understanding inheritance

For thousands of years, human lives have depended on ourunderstanding of inheritance. Why? (Picture suggests ananswer.)



Basic concepts

Definition: Biological inheritance

Biological inheritance, or simply inheritance, refers totransmission of qualities from parent to offspring.

Remark: The concept of inheritance simply refers to theobservation that offspring tend to resemble their parents.

Definition: Trait

A trait is an inherited characteristic of an organism, eitherphysical or behavioral.

Example: In humans, hair color, eye color and some aspects ofpersonality are traits.



Genetics and its 2 subdisciplines

Definition: Genetics

Genetics is the branch of biology that studies patterns andmechanisms of (i) heredity and (ii) variation among organisms.

Note: Genetics studies both inherited and non-inherited(environmental) aspects of traits; the latter causes variation.

Definition: Transmission genetics (this unit)

Transmission genetics is the study of how genes aretransferred from one generation to another.

Definition: Molecular genetics (next unit)

Molecular genetics is the study of molecular mechanisms ofgenetics, including the structure and function of geneticmaterial.



A common 19th century hypothesis of genetics

Genetic material thought to be “generative fluid.” Inheritancewas thought to be like mixing blobs of paint.

Example: Flower color. What colors should offsprings’ flowersbe under this conception?



Prediction from generative fluid notion

All offspring should have pink flowers.



If true, what do we expect in the next generation?

Generation

1

Males Females



And the next generation?

Generation

1

Males Females

2



And the next?

Generation

1

Males Females

2

3



And after an indefinite number of generations?

Generation

1

Males Females

2

3

∞

.

.

.

.

.

.

.

.

.



Apply the first principle of scientific thought

“It doesn’t matter how beautiful your theory is, itdoesn’t matter how smart you are. If it doesn’t agreewith experiment, it’s wrong.”


Inheritance and genetics Mendel’s study Methods Initial results

Fitting theory to experiment with exquisite care

Gregor Mendel



Flower anatomy



Mendel’s basic experimental design



Mendel’s first observations

Experiment A1:




Experiment A1:

Can the generative fluid notion be saved?




Experiment A1:

Yes! If all the fluid comes from the smooth (round) parentCan the generative fluid notion be saved?




Experiment A1:

Can the generative fluid notion be saved now?




Experiment A1:

NO! No way to get wrinkled fluid to the F2




Experiment A2:

P Yellow cotyledon variety × Green cotyledon variety

↓F1

F2




Experiment A2:


↓F1 All yellow cotyledon × self

↓F2




Experiment A2:


↓F1 All yellow cotyledon × self

↓F2 6022 yellow cotyledon : 2001 green cotyledon



Summary of Mendel’s 1-trait crosses

Trait 1 Trait 2 F1 F2* Ratio

Spherical seed Wrinkled seed All Spherical 5474 : 1850 2.96:1Yellow Cotyl. Green Cotyl. All Yellow 6022 : 2001 3.01:1Purple Flower White Flower All Purple 705 : 224 3.15:1Inflated pod Shriveled pod All Inflated 882 : 299 2.95:1Green pod Yellow pod All Green 428 : 152 2.82:1Axial Flower Terminal Flower All Axial 651 : 201 3.14:1Tall Stem Dwarf Stem All Tall 787 : 277 2.84:1

* Larger number always same as F1.


lecture 2.01: mendel's study - scottsdale community college

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