© K. Malone, 2005 Chapter 11 Introduction to Genetics P. 64.

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Chapter 11Introduction to GeneticsP. 64

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XFirst Generation (F1)

100% pink!!!

Second Generation (F2)

X

3 pink, 1 blue - ¾ pink (75%), ¼ blue (25%)How did this How did this

happen?happen?

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Section 11-1

Genetics!!!

• Patterns of Inheritance• You inherit traits (physical

characteristics) from your parents- Heredity!

• Heredity is what makes you unique– Examples of Traits:

• Blue, Green, Brown, Black, Hazel Eye color

• GeneticsGenetics = the scientific study of heredityand its importance in biology

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Gregor Mendel

•Gregor Mendel (1822), an Austrian monk who studied inheritance patterns in pea plants, his work is now considered the foundation of modern genetics– He worked with ordinary

garden peas, planted in the garden at his monastery.

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What Mendel Found• Mendel studied 7 different pea plant

traits that varied from one individual plant to the next (like human traits!)

• These traits had 2 forms, such as either green seeds or yellow seeds, smooth pods or wrinkled pods– He crossed plants with each of the 7

contrasting characteristics and studied their offspring

• P = represents the parent generation

• F (from the Latin word fillius and filia- son and daughter) are the offspring

• F1 = first generation

• F2 = second generation

• Hybrids = offspring of crosses between parents with different traits

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Mendel’s Experiment

P generation

tall short

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Mendel’s Experiment

tall short

F1 generation

tall tall

P generation

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Mendel’s Results

Seed Shape

Seed Color

Seed Coat Color

PodShape

PodColor

FlowerPosition

FlowerHeight

wrinkled green white

round yellow gray

constricted yellow terminal short

smooth greenaxial

tallRound dominant

Yellow dominant

Gray dominant

Smooth dominant

Green dominant

Axial dominant

Tall dominant

All the F1 plants expressed only the dominant trait!

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Mendel’s Principles of Heredity

• Mendel learned 2 principles from these experiments:1. Biological inheritance is

determined by factors (we call them genes) that are passed from one generation to the next, Genes = chemical factors that

determine traits – each trait is controlled by 1 gene that occurs in 2 contrasting forms or alleles

Allele = a different form

of a gene

Hello!

2. Principle of Dominance: some alleles are dominant and others are recessive

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Principle of Dominance

Eeek!

• An organism with a dominant allele for a particular form of a trait will always exhibit that form of the trait

• In other words, if you have the dominant allele, you will express that dominant trait

• An organism with a recessive allele for a particular form of a trait will exhibit that form only when the dominant allele is not present

• In other words, you must have 2 recessive alleles to express the recessive trait

I’m Dominant!! Tall =

TT or Tt

Short = tt

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Where did the recessive traits go?

• Mendel wanted to know why all his F1 plants expressed only dominant traits ?????

• He wondered, “Had all the recessive traits disappeared? Or were they still present in the F1 plants?”

• To answer this question, he allowed his F1 plants to self-pollinate

F1 X F1 F2

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Mendel’s Experiment

P generation

tall short

F1 generation

tall tall

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Mendel’s Experiment

P generation

tall short

F1 generation

talltall

F2 generation

tall tall tall short

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F1 Cross

• Mendel thought the results for his F1 cross were amazing!

• All the recessive traits re-appeared in the F2 offspring!