Mendels Second Experiment Inheritance of Two Traits Dihybrid

Mendel’s Second Experiment Inheritance of Two Traits Dihybrid Cross

Monohybrid Review n How many traits were being looked at during the Mendel’s monohybrid cross? – The cross was between one trait only n What was being crossed in Mendel’s monohybrid cross? – Two purebred organisms for the first cross – Two F 1 Heterozygote organisms in the second

Back Track for a Second n 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) n What about a hybrid species in terms of genotype? – It was a species that had different alleles in its genetic makeup (like Bb)

PXP n When the two parents were crossed, BB X bb, what resulted? n The Results were four heterozygous offspring. n These are the F 1 generation

F 1 X F 1 n When the two F 1 generation were crossed, BB X bb, what resulted? n The Results were three dominant and one recessive in a 3: 1 phenotypic ratio but in a 1: 2: 1 genotypic ratio n These are the F 2 generation

The Law of Segregation n 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? n Mendel completed the monohybrid cross and started to ask and formulate new questions n 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? n He started all over again n He produced purebred plants just like last time with the traits he wanted to examine n 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 next? n He then crossed them again n The P X P ended up yielding what? – The F 1 ended up being all yellow and all round, just like last time – There seems to be some similarity

P X P Dihybrid Cross RY RY ry Rr. Yy Rr. Yy

Then What? n Just like last time he crossed the two F 1 Progeny n 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? n The ratio that he got was? – 9: 3: 3: 1

How to determine the Gametes n Think Back to Grade 9 math (or before maybe) n What was foil? n (x + n) (y + z) = xy + xz + ny + nz

Same rule applies n When looking at the genotypes of the parents to identify the possible gametes perform the same type of foil as we do in math n Rr. Yy = RY + Ry + r. Y + ry

How Many? n 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 n 320 round and yellow n 104 round and green n 101 wrinkled and yellow n 26 wrinkled and green

What did this tell him? n 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 n The second law of inheritance states that the inheritance of alleles for one trait does not affect the inheritance of alleles for another trait n Different pairs of alleles are passed to the offspring independently of each other

The Law of Independent Assortment n This means that offspring may have new combinations of alleles that are not present in either parent

Class Work n Read Pages 136 – 140 (including the Sample problem on page 140) n Complete questions 1 -9 on page 141 questions 1 -3 on page 29 (course pack)