Probability and chance of these punnett diagrams

Hello! I have created two punnet diagrams for X diseases and need to write the probability/chance of the offspring of the carriers being either a non-sufferer or sufferer of the diseases could anybody assist with this as I am a little bit confused. Thank you!

Disease A:

B b

B BB Bb

b Bb bb

Syndrome B:

B b

B BB Bb

B BB Bb

Reply 1

bl0bf1sh

15

are the diseases dominant or recessive?

Reply 2

Courtneyks

OP

8

Hello! sorry I forgot to add that. Disease A is autosomal dominant and B is autosomal recessive :smile:

Reply 3

bl0bf1sh

15

for a dominant condition, someone will have the condition if at least one of the alleles in the genotype is a capital letter (AA or Aa, for example)
for a recessive condition, someone will only have the condition if both alleles in the genotype are lowercase (aa, for example)

Reply 4

Courtneyks

OP

8

Original post by bl0bf1sh

for a dominant condition, someone will have the condition if at least one of the alleles in the genotype is a capital letter (AA or Aa, for example)
for a recessive condition, someone will only have the condition if both alleles in the genotype are lowercase (aa, for example)

So would this mean based on my punnett diagrams that in A: there is a 75% chance that the offspring will be a sufferer, 25% chance that they will not be a sufferer. The probability is 3/4 that the offspring will be a sufferer?

and for B: there is a 0% chance that the offspring will be a sufferer?

What would the chances be that the offspring could be a carrier but not a sufferer for A & B? ( sorry confusing myself the more I think about it!)

Reply 5

bl0bf1sh

15

yes

for the dominant, anyone who has at least one dominant allele has the condition, so all carriers would have the condition
for the recessive, anyone who is heterozygous is a carrier but not a sufferer

Reply 6

Courtneyks

OP

8

Original post by bl0bf1sh

yes

for the dominant, anyone who has at least one dominant allele has the condition, so all carriers would have the condition
for the recessive, anyone who is heterozygous is a carrier but not a sufferer

Ah Auto correct changed the letters on my diagram so they were slighly wrong!

Diagram A (dominant) should be

B b

B BB Bb

B BB Bb

So does this mean: There is a 100% chance that the offspring will be a sufferer of the gene? or 50% that they will be a carrier ( due to the two hetro geno in the table)

-----

And for B (recessive)
Does this mean that actually There is a 25% chance of the offspring being a sufferer (bb x 1), a 50% chance the offspring will be a carrier (Bb x 2) and a 25% chance the offspring will be a non carrier/sufferer(BB x 1)? Not sure the probabilities for this one.

B b

B BB Bb

B Bb bb

Sorry, I am really confused with this not sure why this seemingly simple topic is confusing me so much. It's the probability and chance that I have such an issue understanding. Especially with the first diagram. Thank you!

Reply 7

bl0bf1sh

15

yes, for A (dominant), there is a 100% chance that each of the offspring will have at least one dominant (B) allele, so 100% of the offspring will have the condition
and for B (recessive), there is a 25% chance that each offspring will have the condition (bb), and 75% that the each offspring will not: 25% BB (homozygous dominant, so not a carrier) and 50% Bb (heterozygous, therefore a carrier of the recessive allele (b) but since they have a dominant allele (B) they do not have the condition)

I find it helps to do some highlighting and circling on your diagram to show the phenotype of each genotype, which helps work out the probabilities

carriers tend to be associated with diseases inherited as recessive traits, as the individual is capable of passing on the recessive allele (they "carry" the allele for the condition)

Probability and chance of these punnett diagrams

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