Transcript 11-3 Exploring Mendelian Genetics

Chapter 11
Introduction To Genetics
Section 11-3
Exploring Mendelian
Genetics
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Gregor Mendel
Wanted To Know If:
Segregation Was Truly Independent
or
Does The Segregation Of One Pair
Of Alleles Affect The Segregation
Of Another Pair Of Alleles????
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Independent Assortment
Mendel Performed A
Two Factor Cross
– He Crossed
Round/Yellow
– With
Wrinkled/Green
RRYY
rryy
This Provided The F1 Hybrids That
He Needed.
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Independent Assortment
F1 Hybrid
RrYy
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Independent Assortment
9:3:3:1
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Two Factor Cross F2
All F1 Plants Were
Heterozygous or Hybrid
In The F2 Cross Would
1. The Dominant Alleles Stay Together
2. Or Would They Segregate Independently
So Any Combination Of Alleles Would Be
Possible??????
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Two Factor Cross F2 Results
556 Seeds Produced
315 Round/Yellow
F1 Parental
Phenotypes
32 Wrinkled/Green
Plus
209 Unique Phenotypes Can Only Form
Via
Independent
9:3:3:1
Assortment
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Two Factor Cross F2 Results
The Alleles For Seed Shape And
Color Segregated Independently
INDEPENDENT ASSORTMENT did occur.
Therefore These Alleles
DO NOT
Influence Each Others
Inheritance
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Key Concept
The Principle Of Independent
Assortment States That
Genes For Different Traits
Can Segregate Independently
During The Formation Of Gametes.
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Summary of Mendel’s Principles
1. Inheritance of Biological
Characteristics Is Determined By
Individual Units Known As Genes.
In Organisms That Reproduce
Sexually, Genes Are Passed From
Parents To Their Offspring.
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Summary of Mendel’s Principles
2. Where Two or More Forms Of The
Alleles Exist,
Some Forms Of The Allele Many
Be
Dominant
And Others May Be
Recessive.
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Summary of Mendel’s Principles
3. In Most Sexually Reproducing
Organisms, Each Adult Has Two
Alleles In Each Gene – One From
Each Parent
4. These Alleles Are Segregated
From Each Other When Gametes
Are Formed.
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Summary of Mendel’s Principles
5. Alleles Contained In Different
Genes Usually Segregate
Independently Of One Another
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Beyond Dominant & Recessive Alleles
Key Concept:
Some Alleles Are Neither
Dominant Nor Recessive, And
Many Traits Are Controlled By
Multiple Alleles or Genes.
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Incomplete Dominance
Red Flower Crossed With White Flower
Results In Pink Flower.
In Incomplete Dominance The
Heterozygous Phenotype Is
Between The Homozygous
Phenotypes.
(Both Alleles Expressed In One Cell)
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Codominance
• Both Alleles Completely Expressed
Red Hair Cattle Crossed With White
Haired Cattle Produce Roan (Pink
Brown) Cattle That Have Both
Colored Hairs.
(Both Alleles Expressed Independently)
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Codominance
RED
WHITE
ROAN
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Multiple Alleles
• A Gene Is Controlled By >2 Alleles.
– Individuals Can Only Have 2 Alleles
– Populations Can Have More Than Two
• Rabbit Fur Color
• Blood Types
• Eye Color
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Multiple Alleles
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Multiple Alleles
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Multiple Alleles
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Polygenic Traits
• Phenotypes Produced By The
Interaction Of Several Genes.
– Human Skin Color Is Controlled By
More Than 4 Different Genes.
– Eye Color is Controlled By At Least 3
Genes
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Applying Mendel’s Principles
Thomas Hunt Morgan – early 1900’s
– Drosophila melanogaster
• Easy To Raise
• Produces Numerous Offspring Every 14
Days
• Large Chromosomes
• Susceptible To Mutagens
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