11.1:

The Work of

Gregor MendelBiology

Learning Goals

We will describe how an organism gets its unique

characteristics and how different forms of a gene

are distributed to offspring.

We will explain how geneticists use the principles

of probability to make Punnett squares, explain

the principle of independent assortment, and

explain how Mendel’s principles apply to all

organisms.

Introduction VideoBill Nye: 100 Greatest Discoveries/ Genetics

Where does an organism get its

unique characteristics?

Every living thing - plant, animal, bacteria,

human – has a set of characteristics

inherited from its parents.

The scientific study of inheritance, known as

GENETICS, is the key to understanding how

traits are passed from parents to offspring,

thus making each organism unique.

Mendel and His Peas

Gregor Mendel worked with the garden

pea.

Why the garden pea?

Garden peas are small & easy to grow.

They reproduce quickly and produce hundreds of

offspring.

Help us understand how other organisms pass

traits to offspring without taking years to figure

out.

The Role of Fertilization Male parts of the pea plant produce SPERM

Female parts of the pea plant produce EGGS

Fertilization

SPERM and EGG join to produce an EMBRYOencased in a seed that will eventually, under the right circumstances, grow into a new pea plant.

Pea flowers normally self-pollinate, which means they get ALL of their characteristics from a SINGLEPARENT.

These plants were called “TRUE-BREEDING” plants and would produce offspring identical to themselves.

Traits Also known as characteristics

Traits vary from individual to individual

Mendel studied 7 traits of the garden pea, each

trait had 2 options.

TRAIT OPTIONS (ALLELES)

Plant height Tall Short

Flower color Purple White

Flower location Axial (mid-stem) Terminal (end of stem)

Pea/seed color Yellow Green

Pea/seed shape Round Wrinkled

Pod color Green Yellow

Pod shape Smooth Constricted

Mendel’s Experiment

Mendel decided to cross groups of TRUE-BREEDING

plants.

To cross plants means to take pollen from one plant

and dust it onto the flower of another plant.

Cross-pollinating plants allowed Mendel to breed

plants with different traits to see what traits the

offspring would express.

The offspring created are called HYBRIDS.

Law of Segregation

Before Mendel, scientists believed in the “Blending Model” prediction, where traits from the parents blended in their offspring and passed that trait onto their own offspring

Law of Segregation How are different forms

of a gene distributed to offspring?

Gametes are the sex cells of organisms (sperm & egg)

During segregation, the alleles for each gene separate or segregate from each other, so that each gamete has only one allele for each gene.

Ear Lobes

Free Ear Lobes Attached Ear Lobes

Hitchhiker’s Thumb

Dimples

Dimples No Dimples

Tongue Rolling

Tongue Rolling Unable to roll tongue

Hairy Fingers

Hair on Fingers No Hair on Fingers

Widow’s Peak

Widow’s Peak No Widow’s Peak

Chin Type

Cleft Chin Smooth Chin

Freckles

Freckles No Freckles

Hair Style

Curly Hair Straight Hair

Hair Color

Dark Hair Light Hair

Eye Color

Brown EyesGrey, Green, Hazel, or Blue Eyes

Red Hair

Non-Red Hair Red Hair

Vestigial Ear Bump

Feature Dominant Trait Number Recessive Trait Number

A

Free Ear Lobe Attached Ear Lobe

B

Roll Tongue Can’t Roll Tongue

C

Widow’s Peak No Widow’s Peak

D

Ear Bump No Ear Bump

E

Freckles No Freckles