Transcript Genetics PPT

Genetics
Why Do You Look Like You Do?
What You Should Learn From
This Presentation

You should know the definition of each of
the bold, underlined words
 You should know the general theme of the
presentation
 We will go over the presentation as a group,
be prepared to discuss it
Genetics
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Defined as the study of heredity.
History of Genetics
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10,000 years ago, farmers in Egypt bred
wheat
 4,000 years ago, Asian horse breeders kept
records of animal traits
 Humans have been controlling the traits of
crops and livestock since before the
beginning of history
Gregor Mendel
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1822-1884
Lived in Austria (now part of Czechoslovakia)
Was an Augustinian monk
Conducted breeding experiments in the monastery
garden from 1856-1864
Published in 1866 (just after Darwin was
published)
No one cared until 35 years later (about 1900)
Gregor Mendel
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Experiment consisted of keeping amazingly
accurate records of the garden pea
 He chose the pea plant because he could get pure
strains that had been produced over years by
gardeners
– The strains had many different varieties with
contrasting traits
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He planted and kept records of over 30,000 plants
Gregor Mendel’s Results
Trait
First Generation
(F1)
Second
Generation (F2)
Ratio
Yellow vs. Green
Peas
All yellow
6022 Yellow
2001 Green
?
Round vs. Wrinkled
Peas
All round
5474 Round
1850 Wrinkled
?
Inflated vs.
Constricted Pods
All Inflated
882 Inflated
299 Constricted
?
Long vs. Short Stems
All Long
787 Long Stems
277 Short Stems
?
Colored vs. White
Flowers
All Colored
705 Colored
224 White
?
Axial vs. Terminal
Flowers
All Axial
651 Axial
207 Terminal
?
Green vs. Yellow
Pods
All Green
428 Green
224 Yellow
?
Gregor Mendel’s Results
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Did you see a trend?
 What is the final F2 ratio for each of the
traits?
Gregor Mendel’s Results
If you didn’t, go back and take a look again
 Notice that the trait in the F1 generation is
always the larger number in the F2
generation
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Gregor Mendel’s Results
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If you figured out the F2 ratio, you should
have noticed something else
 Almost all of them are close to 3:1
Gregor Mendel’s Results
Trait
First Generation
(F1)
Second
Generation (F2)
Ratio
Yellow vs. Green
Peas
All yellow
6022 Yellow
2001 Green
3.01:1
Round vs. Wrinkled
Peas
All round
5474 Round
1850 Wrinkled
2.96:1
Inflated vs.
Constricted Pods
All Inflated
882 Inflated
299 Constricted
2.95:1
Long vs. Short Stems
All Long
787 Long Stems
277 Short Stems
2.84:1
Colored vs. White
Flowers
All Colored
705 Colored
224 White
3.15:1
Axial vs. Terminal
Flowers
All Axial
651 Axial
207 Terminal
3.14:1
Green vs. Yellow
Pods
All Green
428 Green
224 Yellow
2.82:1
Gregor Mendel’s Results
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Why did all of the F2 generations have a
three to one ratio when the F1 generation
were all one trait?
 Because the pure parents each gave a gene
or “factor” to each of the F1 offspring and
one of those genes were dominant over the
recessive gene
Gregor Mendel’s Results
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Yet, some of those F1 generations passed
on the the genes to their F2 generations
Gregor Mendel’s Results
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The F2 generation must have had some of
the traits from the P1 generation, but we
were unable to see the recessive traits.
– They were masked or covered by the dominant
trait.
Mendel’s First Principle
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Principle of Dominance and Recessivness
– Each trait is controlled by a pair of factors
(chromosomes)
– The dominant factor masks or hides the
recessive factor
Genotype vs. Phenotype
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Genotype describes the genetic make-up of
the organism
– The actual genes
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Phenotype describes the physical make-up
of the organism
– What traits does the organism show
Mendel’s Second Principle
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The Principle of Segregation
– Heredity factors are determined by distinct
factors
– For each trait, an individual carries two factors
for each trait
– The two factors of each trait segregate and end
up in separate gametes
Mendel’s Second Principle
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Today, those factors are called genes
– Part of the DNA
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Each gene codes for one trait
– Those are called alleles
Mendel’s Second Principle
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If you did the cross below, what is the
probabilty of each genotype?
Monohybrid Cross
Tt x Tt
T
t
T
TT
Tt
t
Tt
tt
Monohybrid Punnett Squares
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Now you try some:
– Tt x tt
– Tt x TT
– TT x tt