Mendel’s Peas pg. 648

• Describe Mendel’s genetics experiments

• Identify the factors that control the inheritance of traits in organisms

• Explain how genetics use symbols to represent alleles

Vocabulary• Heredity-• purebred-• gene-• allele-• dominant allele-• recessive allele-• hybrid-• Genetics-• Traits-

Questions:1.What factors control the

inheritance of traits in organisms?

2.What is a purebred?3.If a pea plant has a tall stem,

what possible combinations of alleles could it have?

Gregory Mendel 1851Priest, Teacher, Gardner

• Pea plants have different traits - different physical characteristics

• similar to parents-heredity - passing of traits from parents to offspring)

• 10 yrs. of study & 1000’s of plants to understand heredity

• his work laid foundation for genetics-study of heredity

Flowering Pea Plant

• traits in only two forms

• produce many offspring

• able to collect much data

• developed method of cross pollinating

Genetics of Pea Plants

Mendel’s Experiments-wanted to cross tall with short purebred plants - always produce the same form of trait as

the parent• Tall purebred

• Tall offspring

• Short purebred

• Short offspring-self pollinate for many generations-offspring will always be identical to parent

Experiment #1

• Tall Purebred• parental generation=P

• Short Purebred• parental generation=P

X

F1 generationfilial “son” in latin

Surprise!• F1 generation-------- All Tall

• short trait disappeared ?

• Next, let grow and let self pollinate

Surprise again!!!F2 (second filial generation)

• Mix of tall and short• no F1’s were short;

shortness trait reappeared

What? I don’t get it!

Inferences made by Mendel• Individual factors control inheritance of traits• Factors controlling traits exist in pairs; male

and female• One factor can ‘mask’ (hide) another,

example: Tall masked short height• Scientists call factors that control traits,

‘genes’.• Different form of genes are alleles.

‘Gene’ that controls ‘Stem Height’

• T• s• T

• T• s• s

Combination of two

Dominant allele (Capitalized)-always shows up in organism when present

Recessive allele (lower case)-masked or covered up when dominant allele is present

alleles

Understanding Mendels Crosses

• 1 tall allele ‘ D’• 1 short allele ‘ r’

• 1 tall, 1 short =hybrid-two different alleles for the trait

TT TT TT Ts

TT TT Ts ss

Mendel’s Contribution

• 1866 submitted paper to Scientific Society; other scientists deemed not important, too oversimplified

• no phones or communication• forgotten for 34 years• 1900 three other scientists came upon

same conclusion and recognize Mendels’ work

• Father of Genetics

Mendel quiz1. Different forms of a gene.2. An allele that is masked when a dominant

allele is present3. An organism that always produces offspring

with the same form of a trait as the parent4. An allele whose trait always shows up in the

organism when the allele is present.5. The passing of traits from parents to

offspring.6. A segment of DNA on a chromosome that

codes for a specific trait.7. An organism that has two different alleles for

a trait.

Questions:

8. What factors control the inheritance of traits in organisms?

9 & 10. If a pea plant has a tall stem, what possible combinations of alleles could it have?

Answers to Mendel quiz1 pt. each

1. Allele2. Recessive allele3. Purebred4. Dominant allele5. Heredity6. Gene7. Hybrid8. Genes9 & 10. TT, Ts.

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