Mendelian Inheritance & Principles
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Transcript of Mendelian Inheritance & Principles
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Mendelian Inheritance & Principles
November 20, 2007BIO 184
Dr. Tom Peavy
(Chapter 2- Brooker Text)
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–Theory of Pangenesis
–Theory of Preformationism
–Blending Theory of Inheritance
Central Question
How are traits inherited?
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Theory of preformationism (homunculus)
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Human Genome Project
Skip Ahead to the 21st Century:
• We know the genetic information (DNA) is organized within Chromosomes
•We receive one homologous chromosome from each parent ♂n + ♀n = 2n (new unique individual)
http://www.ncbi.nlm.nih.gov/
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P Cross F1 generation F2 generation Ratio
Tall X dwarf stem
All tall 787 tall, 277 dwarf
2.84:1
Round X wrinkled seeds
All round 5,474 round, 1,850 wrinkled
2.96:1
Yellow X Green seeds
All yellow 6,022 yellow, 2,001 green
3.01:1
Purple X white flowers
All purple 705 purple, 224 white
3.15:1
Axial X terminal flowers
All axial 651 axial, 207 terminal
3.14:1
Smooth X constricted pods
All smooth 882 smooth, 229 constricted
2.95:1
Green X yellow pods
All green 428 green, 152 yellow
2.82:1
DATA FROM MENDEL’S MONOHYBRID CROSSES
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Mendel’s Law of Segregation
During gamete formation, the paired factors segregate randomly so that half of the gametes received one factor and half of the gametes received the other
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Dihybrid Crosses
Crossing individual plants that differ in two traits
• For example– Trait 1 = Seed texture (round vs. wrinkled)– Trait 2 = Seed color (yellow vs. green)
• There are two possible patterns of inheritance for these traits
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P Cross F1 generation F2 generation
Round,
Yellow seeds X wrinkled, green seeds
All round, yellow
315 round, yellow seeds
101 wrinkled, yellow seeds
108 round, green seeds
32 green, wrinkled seeds
DATA FROM DIHYBRID CROSSES
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Interpreting the Data
• The F2 generation contains seeds with novel combinations (ie: not found in the parentals)– Round and Green– Wrinkled and Yellow
• These are called nonparentals
• Their occurrence contradicts the linkage model
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P Cross F1 generation F2 generation Ratio
Round,
Yellow seeds X wrinkled, green seeds
All round, yellow 315 round, yellow seeds
101 wrinkled, yellow seeds
108 round, green seeds
32 green, wrinkled seeds
9.8
3.2
3.4
1.0
DATA FROM DIHYBRID CROSSES
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Law of Independent assortment
During gamete formation, the
segregation of any pair of
hereditary determinants is
independent of the segregation of
other pairs
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Problem Solving
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TtYy x TtYy
Dihybrid Cross
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TtYy x ttyy
What is the expected phenotypic ratio among offspring?
Problem Solving
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Tt RR x Tt RR
What fraction of the progeny will be Tall and Round?
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(pg 38)
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Alternative = Forked Line Method
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Alternative = Forked Line Method
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Alternative = Forked Line Method
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Tt RR Yy x Tt RR Yy
What fraction of the progeny will be Tall, Round, and Green?