Mendel

1
Mendels Second Experiment

• Inheritance of Two Traits
• Dihybrid Cross

2
Monohybrid Review

• How many traits were being looked at during the
  Mendels monohybrid cross?
• The cross was between one trait only
• What was being crossed in Mendels monohybrid
  cross?
• Two purebred organisms for the first cross
• Two F1 Heterozygote organisms in the second

3
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)

4
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

5
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 31 phenotypic ratio but in a 121
  genotypic ratio
• These are the F2 generation

6
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

7
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

8
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)

9
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

10
P X P Dihybrid Cross
RY RY RY RY
ry RrYy RrYy RrYy RrYy
ry RrYy RrYy RrYy RrYy
ry RrYy RrYy RrYy RrYy
ry RrYy RrYy RrYy RrYy
11
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

12
Whats The Ratio?

• The ratio that he got was?
• 9331

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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

15
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

16
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

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What did this tell him?

• The ratio of 9331 could be explained if the
  alleles from one trait were inherited
  independently of the alleles for another trait
• The Law of Independent Assortment

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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

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The Law of Independent Assortment

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

20
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)