genetics, crossing over

[batista_123]

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there are 2 linked recessive diseases. their genes are 20 centimorgans apart. 2 people, who are both are AaBb, marry. what is the probability that their child will not have either recessive disease?

my question is about this part of the answer:

the answer says the parents' gametes are
Ab 40%
aB 40%
AB 10%
ab 10%

my question is, how do you know the gametes are not
AB 40%
ab 40%
Ab 10%
ab 10%
?
never mind, i think i need to follow the pedigree and the pedigree should tell me

 

[ChemEngSoonMD]

there are 2 linked recessive diseases. their genes are 20 centimorgans apart. 2 people, who are both are AaBb, marry. what is the probability that their child will not have either recessive disease?

my question is about this part of the answer:

the answer says the parents' gametes are
Ab 40%
aB 40%
AB 10%
ab 10%

my question is, how do you know the gametes are not
AB 40%
ab 40%
Ab 10%
ab 10%
?
never mind, i think i need to follow the pedigree and the pedigree should tell me

It has to tell you if the Chromosome are AB / ab or aB / Ab before crossing over. Or you have to find out.