A tall plant of unknown genotype is test-crossed (meaning it is crossed with a r

Question

A tall plant of unknown genotype is test-crossed (meaning it is crossed with a recessive tt plant). Of the offspring, 869 are dwarf and 912 are tall. What is the genotype of the unknown parent, is it TT or Tt? Show the cross to prove it In humans, tongue rolling is a dominant trait, those with the recessive condition cannot roll their tongues. Bob can roll his tongue, but his mother could not. He is married to Sally, who cannot roll her tongue. What is the probability that their first born child will not be able to roll his tongue? In goats, a recessive gene causes the goats to "faint" when they are startled A farmer breeds two goats (that have never fainted) and their first offspring faints two day after its birth. What must the parent's genotypes have been? Show the cross to prove it

Explanation / Answer

Tall 912

Phenotypic Ratio Dwarf: Tall= 869:912= 1:1

Genotype will be Tt

Cross over   

Tt X tt

Gametes : T, t, t, t

Genotype Tt Tt tt tt= 1:1

Bob Genotype: Aa

Bob’s Mother : aa

Sally: aa

Cross Over

Aa X aa

Aa , Aa, aa, aa = 1:1

Probabilty of first born is recessive = ½

Parents genotype must be heterozygous which is Aa

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