Fall 2022 Mid-Term Genetics Class Test Solutions – Emory University
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Briefly Describe Other Blood Grouping Systems Apart from the ABO
While the ABO groups are vital in transfusion, they are by no means the only groups. Second to be discovered was the M, N, MN system. Two genes control this. English people are 32% M, 19% N and 48% MN. To be N both parents cannot be M. To be M both parents cannot be N. and to be MN means that both parents cannot be exclusively M or N, all of which is crucial evidence for the paternity courts. Once again, the geographical distribution is odd. Blacks, Pacific Islanders and Aboriginal Australians are rich in N and weak in M. Eskimos, Red Indians, Welsh, Chinese and Japanese are rich in M and weak in N (the Welsh are never good at conforming). There is slightly more sense in the MN distribution than with the ABO's, but that Bering Straits migration is still awry. Asiatic Mongoloids have many N's among them; American Mongoloids hardly any.
Since Landsteiner started the blood group avalanche, more and more have been found, such as the MNSs, the Rh-HR (the famous Rhesus factor), the P groups, the Kell, the Lutheran, the Duffy, the Kidd, the Lewis, the Diego, the Hunter and Henshaw, the Sutter-most of which are named after the patients in whose blood they were first found. Consequently do not leave fingerprints or blood at the scene of the crime, particularly at some foreign scene. Any European's blood can be distinguished from a West African's ninety-five times out of a hundred, thus narrowing the field of suspicion abruptly.
It is reasonable to wonder where all these blood groups came from. Consequently, tests have been done on the higher animal species. Chemically there are differences but many more similarities. Most monkeys are A or B, rarely both. The gorillas seem to be either A or B, the chimpanzees are mainly A and sometimes O. the orangutans and gibbons A, B or AB. It is strange that O; the most frequent group in man, is the rarest (bar 10% of the chimpanzees) in the apes and monkeys. The evidence is insufficient to provide any powerful pointers towards the origins of man. Perhaps the less well-known groups, with perhaps less evolutionary influence, will provide better clues when comparative work has been done.
Describe The Rhesus Concept, Distribution, And Transfusion
If you are a Rhesus-negative girl (one-sixth of British girls are) marry a Basque, or, better still, a Walser of Switzerland. But think twice about Pacific Islanders, Australian Aborigines and American Indians. You may be making life marginally easier for yourself and your obstetrician, and considerably easier for your babies, if you choose a Rhesus-negative mate. Thirty-six per cent of the Basques are eligible, only 16% of Englishmen, but no Red Indians, Papuans or Aboriginal Australians. Also, hardly any Chinese or Japanese are Rhesus-negative. If you do choose a Papuan, or even a Rhesus-positive Englishman, there is a chance (about 72%) that your baby will be Rhesus-positive, like his father, unlike you. This could mean trouble, but such a marriage with such a baby is only troublesome in 2% to 5% of cases.
Reasons were at first poorly understood, but whether or not there was fetal bleeding at birth, causing the mother's blood to meet the fetus, is now known to be highly relevant to the fate of the next child. So are the ABO blood groups because, if both parents have different ABO groups, the new babies are less likely to suffer from Rhesus trouble. This stroke of good fortune is linked with the massive resentment between one ABO blood group and another blurring the minor resentment between the two Rhesus groups. Anyway, if you, a Rhesus-negative female, do mate with a Rhesus-positive male, there will be fewer Rh- incompatible fetuses if you are O and he either A, or B, or AB. Things are less well from the Rh point of view if you are A and he is either O or A.
This trouble, this Rh-incompatibility of the fetuses, has many names such as Hemolytic disease of the Newborn, Erythroblastosis fetalis, Kernicterus, and Icterus gravis neonatorum. Whatever the name it is basically a destruction of the baby's red blood cells. The mother (having produced antibodies against her Rh-positive fetus) is doing the destroying. So the baby becomes anemic and jaundiced and, were it not for transfusions, would die seventy-five times out of a hundred, sometimes before birth. Recent treatment was fairly straightforward. The sooner the baby was born the better (within reason), for the sooner it had left its mother's destructive (hemolytic) influence the better. Then its blood was exchanged to get rid of all those maternal antibodies and in 1963 a fetus’s blood was even changed before its birth.
Although such ante-natal transfusion is an extremely modern technique, it was outmoded almost at once by an even better system for protecting the victims of Rhesus incompatibility. Professors C. A. Clarke, P. M. Sheppard and others at Liverpool University, after working with Rh-negative male volunteers, devised a way of preventing Rh-negative mothers from producing antibodies against their Rh-positive offspring by using gamma globulin with what is known as a high titre of Anti-D. This new system, being one of prevention rather than cure, has enabled one in 200 of all British babies (roughly 3,000 a year) both to survive more frequently and have an easier time of it than formerly. The period, therefore, between the first comprehension of Rhesus incompatibility and the discovery of an effective counter- measure was less than three decades.
The clue which led to the unravelling of this story at the start of World War Two was that virtually no first babies were affected, with one vital exception. If the Rh-negative mother had ever received a transfusion the chances were (with 84% of us being Rh-positive) she had received Rh-positive blood; hence she could have become sensitized, hence the preparation of Rh-antibodies, hence her firstborn's blood being cruelly attacked. Nowadays no Rh-negative woman before her menopause is given Rh-positive blood. The situation is reasonably in hand. A fascinating upsetting of the situation came from Sweden in October 1965 and was published in The Lancet. A girl, Rh-negative, aged twenty-four, had been a virgin when married in 1961. Consequently, she had had no earlier children or abortions and no chance to get sensitized from Rh-positive blood. Also, she had never had a transfusion. But her first baby was born jaundiced, and she was full of Rh-antibodies. Her second baby was similar. It was all a mystery until she admitted receiving blood, when aged nine, during a girls' 'brotherhood' ceremony. The amount transfused was presumably small, but Lund University doctors think it could have done the trick and sensitized her against her first child born a dozen years later. Anyway, they sought out and found her blood brother. Sure enough, she was Rh-positive.
Although the ABO groups have been linked with disease in a few cases, the advantages or otherwise of being Rh-positive or negative are still totally obscure. As Sir Peter Medawar puts it (and he rarely misses the opportunity of a happy phrase) the Rh blood types are associated with nothing except the unqualified incubus of transfusion accidents. It would seem better for the human race if all of us had similar Rh blood (and similar Kell blood too, for the same kind of story exists with that grouping). Why, therefore, the dissimilarity? There is still no explanation nearly half a century after the Rh discovery. "It is not known,' says Medawar; 'it is merely being groped after."
How Can MN Blood Grouping Be Used to Determine Paternity in Courts?
If the baby is MN and mother is M the father cannot be M
The MN test frees a man from responsibility in about 18% of cases. For the Rh test (if both parents are Rh-positive, the child cannot be Rh-negative; if both parents are negative, the child cannot be positive), the maximum chance of exclusion in Western Europe is about 25%. With all three blood tests being used any man has at least a 50% chance of disproving his paternity, and it could be more (75%) if further blood groups are tested. At present most men wrongfully accused of fathering children can prove their innocence by blood group tests. In the world of fact- and the courts - fewer get off. Many women must, therefore, be telling the truth when they point the finger.
In Germany one hundred children plus their correct fathers were once examined by an expert independent panel. (Such paternity experts have a high status in Germany and Scandinavia, not so in Britain.) Using customary methods (and merely looking at parents plus offspring without any recourse to blood testing) the examiners had to decide whether it was probable, improbable or not determinable that the children were correctly assigned. The results were emphatic. Ninety-three of the children were 'probably' the sons of their fathers (varying from 'more probable than not right up to 'probable to a degree bordering on certainty); seven of them were not determinable; but none were said to be definitely not the sons of their fathers. In other words, like produces likeness-an adage more correct, biologically, than like producing like. Like producing like implies duplication, much like a printing machine. In biology, certainly above the most primitive level, the offspring is only similar to its parents, not the same.
What Other Genetic Features Are Commonly Used to Determine Paternity?
Apart from blood and resemblance there are genetic extras like eye and hair color. When both parents are blue-eyed all their children ought to be blue-eyed, but occasionally an incomprehensible brown eye creeps - legitimately in. Two red-haired parents ought to have all red-haired children. And the same sort of thing goes for parents both tall, or both with attached ear lobes, or both with straight hair, or both blond. They are more likely to have tall, attached ear lobe, straight haired and blond children. Tall parents may produce short children, but on average they do so less frequently than short parents. Some characteristics obey definite rules, notably when only one pair of genes is involved (as with blue eyes). Some obey or follow probability, as when many genes are involved (like height and hair). Both types have a part to play in linking children with the parents who produced them.
In a blond, blue-eyed, tall, fair-haired community these particular characteristics are valueless in assessing paternity, and the infrequent ones are more important. In Norway a normal mother produced a brachyphalangic (short-fingered) child, a rare condition. The court asked the accused to hold up his hand. His fingers were short, and he therefore had to pay. Other men have been caught by the presence of hair on the middle digit of one of their fingers. This characteristic also cannot be passed on if it is not possessed. The courts can be wrong in coming to a yes or no answer, but it is possible to calculate - given all the facts about relative frequencies of certain characteristics - how probable or improbable a wrong decision may be (the postman of that Norwegian couple may also have been brachyphalangic, but this is unlikely). Curt Stern has called it 'an exact numerical evaluation of the probability of correctness of a paternity judgment'. The law already possesses a better phrase - beyond all reasonable doubt.
As a tailpiece to paternity there are occasional cases of double- sired twins. In the first to be officially recognized the mother (blood group O and M) produced dissimilar twins, a boy (B,M) and a girl (A, MN). One man could have produced both, by being AB and MN; but no such man was in that mother's life. She had known, as the Bible uses the word, only two men, one being A and MN, the other B and M. The first could not have produced the boy, for where did the lad get his B from? The second could not have produced the girl, for where did she get her A or N from? Both men must have played their part.