Of 31 children born of father-daughter matings, 6 died in infancy, 12 were abnor
ID: 268579 • Letter: O
Question
Of 31 children born of father-daughter matings, 6 died in infancy, 12 were abnormal and died in childhood, and 13 were normal. From this information calculate roughly how many recessive lethal genes we have, on average, in the human genome. (Hint: if the answer were 1, then the daughter would stand a 50% chance of carrying the lethal allele, and the probability of the union’s producing a lethal combination would be 1/2 * 1/4 = 1/8. So, 1 is not the answer.) Discuss the possibility of undetected fatalities in utero in such matings. How would they affect your result?
Explanation / Answer
The probability of not getting a recessive lethal genotype for one gene is 1–1/8 = 7/8. If there are n number of lethal genes then the probability of not being homozygous for any of them is (7/8)n = 13/31. Now we can solve the n, an average of 6.5 recessive lethals is predicted.
If the actual percentage of normal children is less due to be missed in utero fatalities, the average of recessive lethals would be in higher numbers.
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