Download Mendel`s Peas

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
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Hereditypurebredgenealleledominant allelerecessive allelehybridGeneticsTraits-
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 1851
Priest, Teacher, Gardner
• Pea plants have different
traits - different physical
characteristics
• similar to parentsheredity - 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
• Short purebred
• Tall offspring
• Short offspring
-self pollinate for many generations
-offspring will always be identical to parent
Experiment #1
• Tall Purebred
• parental generation=P
X
• Short Purebred
• parental generation=P
F1 generation
filial “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’
alleles
• 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
Understanding Mendels Crosses
• 1 tall allele ‘ D’
• 1 short allele ‘ r’
TT
TT
TT
Ts
• 1 tall, 1 short
=hybrid-two different
TT
TT
Ts
ss
alleles for the trait
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 quiz
1. Different forms of a gene.
2. An allele that is masked when a dominant allele is
present
3. An organism that always produces offspring with
the same form of a trait as the parent
4. 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 quiz
1 pt. each
1. Allele
2. Recessive allele
3. Purebred
4. Dominant allele
5. Heredity
6. Gene
7. Hybrid
8. Genes
9 & 10. TT, Ts.
__/10