Mendel s second experiment
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Mendel’s Second Experiment. Inheritance of Two Traits Dihybrid Cross. Monohybrid Review. How many traits were being looked at during the Mendel’s monohybrid cross? The cross was between one trait only What was being crossed in Mendel’s monohybrid cross?

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Mendel’s Second Experiment

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Mendel s second experiment

Mendel’s Second Experiment

Inheritance of Two Traits

Dihybrid Cross


Monohybrid review

Monohybrid Review

  • How many traits were being looked at during the Mendel’s monohybrid cross?

    • The cross was between one trait only

  • What was being crossed in Mendel’s monohybrid cross?

    • Two purebred organisms for the first cross

    • Two F1 Heterozygote organisms in the second


Back track for a second

Back Track for a Second

  • What exactly was a purebred species in terms of genotype?

    • It was a species that had the same alleles in in its genetic makeup (either BB or bb)

  • What about a hybrid species in terms of genotype?

    • It was a species that had different alleles in its genetic makeup (like Bb)


P x p

P X P

  • When the two parents were crossed, BB X bb, what resulted?

  • The Results were four heterozygous offspring.

  • These are the F1 generation


F1 x f1

F1 X F1

  • When the two F1 generation were crossed, BB X bb, what resulted?

  • The Results were three dominant and one recessive in a 3:1 phenotypic ratio but in a 1:2:1 genotypic ratio

  • These are the F2 generation


The law of segregation

The Law of Segregation

  • What does the Law of Segregation state?

    • It states that inherited traits are determined by pairs of “factors”

    • These factors segregate (separate) in the gametes


What happened next

What happened next?

  • Mendel completed the monohybrid cross and started to ask and formulate new questions

  • What do you think he was thinking of next?

    • He wanted to know if the inheritance of one characteristic influenced the inheritance of a different characteristic


What did he try next

What did he try next?

  • He started all over again

  • He produced purebred plants just like last time with the traits he wanted to examine

  • He bred pea plants that were round and yellow pure plants (dominant for both) and then he did the same for wrinkled and green (recessive for both)


What did he try next1

What did he try next?

  • He then crossed them again

  • The P X P ended up yielding what?

    • The F1 ended up being all yellow and all round, just like last time

    • There seems to be some similarity


P x p dihybrid cross

P X P Dihybrid Cross


Then what

Then What?

  • Just like last time he crossed the two F1 Progeny

  • What do you think he got?

    • He got 9 Yellow and round

    • He got 3 Green and round

    • He got 3 Yellow and Wrinkled

    • He got 1 Green and Wrinkled


What s the ratio

What’s The Ratio?

  • The ratio that he got was?

    • 9:3:3:1


How to determine the gametes

How to determine the Gametes

  • Think Back to Grade 9 math (or before maybe)

  • What was foil?

  • (x + n) (y + z) = xy + xz + ny + nz


Same rule applies

Same rule applies

  • When looking at the genotypes of the parents to identify the possible gametes perform the same type of foil as we do in math

  • RrYy = RY + Ry + rY + ry


How many

How Many?

  • How many plants do you think that Mendel used for this experiment

    • 551 pea plants

    • And of that 551 this was the ratio that he got

  • 320 round and yellow

  • 104 round and green

  • 101 wrinkled and yellow

  • 26 wrinkled and green


What did this tell him

What did this tell him?

  • The ratio of 9:3:3:1 could be explained if the alleles from one trait were inherited independently of the alleles for another trait

    The Law of Independent Assortment


The law of independent assortment

The Law of Independent Assortment

  • The second law of inheritance states that the inheritance of alleles for one trait does not affect the inheritance of alleles for another trait

  • Different pairs of alleles are passed to the offspring independently of each other


The law of independent assortment1

The Law of Independent Assortment

  • This means that offspring may have new combinations of alleles that are not present in either parent


Class work

Class Work

  • Read Pages 136 – 140 (including the Sample problem on page 140)

  • Complete questions 1-9 on page 141

  • Complete questions 1-3 on page 29 (course pack)


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