mendel and his peas - university of pittsburghfacaffs/acie/documents/cm 21-mendel... · 2/29/2012 4...

Mendel and His Peas

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Lecture Learning Objectives: You will be able to:

LO2– To explain how Mendel’s results lead to the principles of particulate inheritance and independent inheritance.

LO1 – To describe Mendel’s work and the hypotheses it generated

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LO1 – To describe Mendel’s work and the hypotheses it generated

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Observations Driving Mendel’s Work

Plant and Animal Breeders noticed that offspring (hybrids) of 2 different individuals often displayed an intermediate like a mix of parental traits.

Hypothesis: Blending inheritance predicts….

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Controlling Fertilization of the Flowers

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Prediction of Blending Hypothesis

Predict that F1 generation have slightly wrinkled seeds

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Mendel’s Monohybrid Cross Results

Parental Generation= pure breeding lines

Offspring – F1 generation– phenotype of male parent

Phenotype of female parent not present

Does this support the Blending Hypothesis? Why or Why not?

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Where did the Wrinkled Trait Go ?

Critical Experiment –female phenotype in F1 is not lost, so “blending “did not occur

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Your Turn Work the monohybrid cross problems in the handout.

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Think About It……

Thanks to digital photography and programs like Photoshop, photography studios can claim to predict what a couple’s child would look like based upon merging images of the putative parents. Explain in genetic terms why this is nonsense.

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Mendel’s Unfortunate Naming Conventions

What is the nature of the dominant allele?

What is the nature of the recessive allele?

Dominate and recessive represent alternative phenotypes.

Dominant does not imply presence, Recessive does not imply absence

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Does Gender Influence Trait Inheritance?

The Reciprocal Cross

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Results of Mendel’s 8 Years of Experiments

What do you notice about the ratio of dominant to recessive phenotype in each cross?

Is the distribution of offspring dependent on the trait studied?

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The Dihybrid Cross and Independent Assortment Do the parental alleles remain together when gametes are formed?

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Your Turn: Predict the Gametes for Dependent Assortment

Female Parent: rryy ( green seeds, wrinkled) Male parent: RRYY (yellow seeds, smooth

Gametes produced by Female Parent: Gametes produced by Male Parent:

Phenotypes of F1 Generation:

Phenotypes of F2 Generation:

ry

RY

RrYy

¼ RYRY, ½ Ryry, ¼ ryry

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Mendel’s result of Dihybrid Cross

Which of Mendel’s hypotheses is consistent with these results?

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Your Turn

Work the dihybrid cross problems in your handout

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But What If You Know The Phenotype But Not The Genotype: The Test Cross

A test cross reveals an unknown genotype

Why do we care? Contribution of homozygous parent known. Allows determination of 2nd parental phenotype.

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Lecture Summary

How did Mendel’s work discredit the hypothesis of Blended Inheritance?

What evidence did Mendel use to support the claim that traits are particulate?

What evidence supports the principle of independent segregation?