The Work of Gregor Mendel

I) Historical Views

A) Blending TheoryA) Mixture of sperm & egg resulted in

progeny that were a "blend" of two parents' characteristics

B) Ignored characteristics that skipped generations-FLAW

II) Gregor Mendel“Father of Modern Genetics”A)His ideas form the backbone

of modern genetics

B) Most pea plants self-pollinate

II) Gregor MendelC) He started with

true-breeding pea plants

1) If allowed to self-pollinate, they produce identical offspring to parent

II) Gregor MendelD) Cross-Pollinated

plants for experiment

E) He studied 7 different traits

1) A specific characteristic, such as seed color or height

Seed Shape

Flower Position

Seed CoatColor

Seed Color

Pod Color

Plant Height

PodShape

Round

Wrinkled

Round

Yellow

Green

Gray

White

Smooth

Constricted

Green

Yellow

Axial

Terminal

Tall

Short

Yellow Gray Smooth Green

Axial

Tall

The 7 traits Mendel studied

II) Gregor MendelF) Called each starting

plant the parent (P)

G) Crossed plants with differing traits , resulting in offspring (F1)

1) F1 crosses between parents of different traits were hybrids

P Generation

Tall Short Tall TallTall Tall Tall Short

Principles of Dominance

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P Generation F1 Generation

Tall Short Tall TallTall Tall Tall Short

Principles of Dominance

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Seed Shape

Flower Position

Seed CoatColor

Seed Color

Pod Color

Plant Height

PodShape

Round

Wrinkled

Round

Yellow

Green

Gray

White

Smooth

Constricted

Green

Yellow

Axial

Terminal

Tall

Short

Yellow Gray Smooth Green

Axial

Tall

The 7 traits Mendel studied

III) Mendel’s ConclusionsA) Inheritance is determined by factors that are passed

from one generation to the next1) Today these factors are called genes2) Alleles: Different forms of a gene

B) Principle of Dominance1) Some alleles are dominant, and others are

recessive2) Need only one dominant allele to see that trait

(TT or Tt both tall)3) Must lack any dominant alleles to see the

recessive trait (only tt is short)

IV) Principle of Segregation

A)What happened to the recessive traits?

B) Mendel cross-fertilized the F1 plants, resulting in F2 offspring with some recessive alleles reappearing

IV) Principle of Segregation

C) Alleles for a gene are segregated from each other during the formation of gametes

P Generation F1 Generation

Tall Short Tall TallTall Tall Tall Short

Principles of Dominance & Segregation

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P Generation F1 Generation F2 Generation

Tall Short Tall TallTall Tall Tall Short

Section 11-1

Mendel Observed the Principles of Dominance & Segregation

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V) Probability

A) The likelihood that a particular even will occur

B) Can be used to predict the outcome of a particular genetic cross

C) Used to predict averages, not precise numbers

D) Use a tool called a Punnett Square

Punnet Squares:

Why did Mendel obsereve what he did?

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Notice all of the results are around a 3:1 ratio

VI) Genetics Key TermsA) Homozygous - when

the two alleles are the same.

B) Heterozygous - when the two alleles are different, in such cases the dominant allele is expressed

V) Genetics Key TermsC) Genotype- genetic make-up.

D) Heterozygous – physical characteristics