Blue skin color can be caused by a mutation in the methemoglobin dioxygenase gen
ID: 182909 • Letter: B
Question
Blue skin color can be caused by a mutation in the methemoglobin dioxygenase gene.
This gene encodes a product that converts methemoglobin to hemoglobin. Hemoglobin binds oxygen in the blood and delivers that oxygen to the muscles and organs throughout the body. Hemoglobin bound to oxygen is red in color. In contrast, methemoglobin bound to oxygen is blue in color. Furthermore, the oxygen is poorly released by methemoglobin.
A pedigree of the Fugate family is shown, with “blue” family members indicated.
Is the trait showing dominant or recessive characteristics? Why?
md is a rare mutated allele of the MD gene, which encodes methemoglobin dioxygenase, and has a frequency of 0.1% in the general population. What would be the frequency for a carrier man to find a carrier wife, assuming the carrier man is meeting a diverse selection of women?
If two carrier parents have a child, what is the chance of the child being blue?
Overall, what is the chance that Ben Stacey, a carrier man, will have an affected child, assuming that he is choosing a wife from a diverse selection of women?
The allele frequency of md in the extended Fugate family is 10%, much higher than in the general population. What is the chance that Ben Stacey will have an affected child, assuming that he is choosing a wife from within this inbred population (i.e. if he marries a distant cousin)?
SUM RULE The sum rule states that the probability of either of two mutually exclusive events occurring is the sum of their individual probabilities. This is like saying what are the chances that 5 pregnancies will result either in all boys or all girls = 1/32 + 1/32 = 1/16.
Ben Stacey marries within the Fugate family, divorces, and marries again. What are the chance that he will have an affected child in either of his marriages?
Pedigree of Hereditary Methemoglobinemia osias Fugate Mary Martin 1700 Sarah Martin Fugate William Smith 1750 William Sarah Benjamin Fugate itc ate Martin Fugate Richard Smith O Alicia Levi Comhs Fugate Hamah Noble Hanna /achanah Fugate Mary O Elizabeth Smith Martin Fugate Ritchie 1800 Fugate C Martin Ritchie lohn Fugate James Ritchie Hanna leanor Fugate Fugate Nancy o Hudson Chades Fugate Lorenzo Fugate Gabriel Fugate Poll itc Manuel ugate Elizabeth ugate 1850 Zachariah Fugate Ma Ritchie Levi Fugate lohn Fugate 1900 13 children, none blue blue ( homozygous) carrier (heterozygous) Alva Stacy Hilda Godsey probably heterozygous 1950 Ben StacyExplanation / Answer
This pedigree shows an autosomal dominant trait or disorder. Autosomal means the gene is on a chromosome that is not a sex chromosome (X or Y). Not all of the offspring inherited the trait because their parents were heterozygous and passed on two recessive genes to those that do not show the trait. None of the offspring of two recessive individuals have the trait.