A genetics question: Tay-Sachs disease is a rare human disease in which toxic substances accumulate in nerve cells. The recessive allele is inherited in a simple Mendelian manner. A woman is planning to marry her first cousin, but the couple discovers that their shared grandfather's sister died in infancy of Tay-Sachs disease.

What is the probability that the cousins' first child will have Tay-Sachs disease, assuming that all people who marry into the family are homozygous normal?

I'll draw the pedigree I have and the work I've done - can't seem to get the right answer, though.

Question

25-11-2016
Biology

Answered

A genetics question: Tay-Sachs disease is a rare human disease in which toxic substances accumulate in nerve cells. The recessive allele is inherited in a simple Mendelian manner. A woman is planning to marry her first cousin, but the couple discovers that their shared grandfather's sister died in infancy of Tay-Sachs disease.

What is the probability that the cousins' first child will have Tay-Sachs disease, assuming that all people who marry into the family are homozygous normal?

I'll draw the pedigree I have and the work I've done - can't seem to get the right answer, though.

Verified Answer :

Related Questions

A farmer wishes to fence a rectangular area behind his barn The barn forms one end of the rectangle and the length of the rectangle is three times the width How

why has the world witnessed globalization in sports

402 round to the nearest ten and hundred

If the National Organization for Women became a third party would it likely be thought of as a single issue party or an ideological party and why or why not

A person who dont have enough calcium in his or her diet is at risk for developing bones

Put these in chronological order election of Abraham Lincoln For sumter Battle of Vicksburg South Carolina secedes lee surrenders at appromattox courthouse Batt

In a recent basketball game between the Storm and the Chargers the number of points scored by the Storm in the first half was equal to the number of points scor

Mary lives in Phoenix shes planning to take her relatives on trips to different parts of the state the table below shows the distances from her home to each des

During Reconstruction many northerners came to the South to help the area rebuild to ensure the former slaves were protected and to ensure the development of st

why are Earths ocean tides influenced by more the moon than by the sun even though the sun is much bigger than the moon

Anonymous Anonymous · Answer 1 · 2016-11-26T04:58:42-05:00

That was the picture, here is the math. Rather than computing all the individual probabilities then multiplying them out, I prefer to compute the probability distribution of each generation and pass it along that way.

The grandfather's probability of being Tt is 2/3. If he is Tt each of his offspring (2a and 2b) has a 1/2 probability of being Tt as well. So overall, the probability for each of his offspring being Tt is 2/3 1/2 = 1/3.

The offspring are independent events (one would hope) so the probability of both his offspring 2a and 2b being Tt is 1/3 1/3 = 1/9.

If 2a is Tt, 2a and TT spouse have a 1/2 probability of producing a Tt offspring. The same argument applies to 2b. The probability that 2a and 2b produce Tt offspring is 1/2 1/2 = 1/4. But the probability that 2a and 2b were Tt is 1/9 as calculated above. So the probability that 3a and 3b are both Tt is 1/4 1/9 = 1/36. So there is a 1/36 chance that 3a and 3b both are carriers.

If 3a and 3b have a child and if they are both Tt carriers, the probability that they will have a tt child is 1/4. The probability that 3a and 3b are both carriers is 1/36. So to obtain the probability of a tt child is 1/4 * 1/36 = 1/144.

I hope that this is the answer that you were looking for and it has helped you.