11.1: The Work of Gregor Mendel Biology
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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
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