TABLE OF CONTENTS
1. high blood pressure / 2. curly & straight hair / 3. IQ / 4. phobias /
Scroll down to a numbered question and click on it to find its answer.
1. Is high blood pressure inherited? – Answer: It can be. Like most complex traits, both genetic and non-genetic factors are involved.
High blood pressure (hypertension) may lead to heart disease, stroke, kidney disease, and a shortened life expectancy.
Upper- and lower-case letters are used for the table below. Among the non-genetic factors contributing to high blood pressure are high alcohol intake (A), high fat diet (F), an inactive life style (I), being overweight (O), and high salt intake (S). By contrast, lower blood pressure is associated with low salt intake (s), low fat diet (f), exercise (i), lower body weight (o), and low salt intake (s). Other non-genetic factors are probably also involved.
Some of the genetic factors contributing to high blood pressure are, among other genes, common variants of these genes: H19 (H), NUCB2 (N), PDE1A (P), RELA (R), and VCL (V). Alternate forms of these genes (h, n, p, r, v) tend to be found in people with lower blood pressure. These genes affect the structure and function of the cells lining the blood vessels.
With a bad lifestyle and bad genes, person 1 has the highest blood pressure and the highest risk for all the health complications that go with it. Person 12 is at the other extreme, with a good lifestyle and good genes, and the lowest risk for the attendant health complications.
Person 2 has high blood pressure because of a bad lifestyle in spite of good genes. Person 3 has high blood pressure because of bad genes in spite of a good lifestyle. More commonly, high blood pressure is a result of a combination of good and bad non-genetic and genetic factors (person 4).
Most people are somewhere in the middle (persons 5-8), as a result of various combinations of genetic and non-genetic factors, different for each person.
The genetic factors are of course inherited from one’s parents, but as the Table shows they are only half the story. Environmental factors are the other half.
2. Why is one person’s hair curly and another’s straight? -- Answer: There’s curly hair, straight hair, and wavy hair; there’s tight-curly, loose-curly, frizzy, kinky, wiry, and woolly hair. None of these terms has a precise definition; nevertheless, the straight-wavy-curly distinction, even if only approximate, is useful for the purpose of investigation.
Although few of the relevant genes have been identified so far, many different genes undoubtedly affect the numbers, sizes, and positions of cells in different places in the base of the hair follicle, where the straight-wavy-curly difference is determined. And with different genes being distributed to eggs and sperm haphazardly, the parent-to-child inheritance of curly/wavy/straight hair does not always follow a predictable pattern. (It has been suggested that curly hair might be dominant over straight hair with wavy hair an intermediate condition, but not all family studies support this conclusion.)
The main difference in curly vs. straight hair is related to differences in the sizes of the cells forming the shaft of the hair. Larger cells on one side of the shaft makes the hair curve in the opposite direction, just as having larger bricks on one side of a brick path would give a curved path. Different types of hair haven’t yet been carefully investigated in this regard, but one would expect that equal-sized cells all around the hair shaft would result in straight hair, and much greater cell-size differences on one side than on the other would give much curlier hair. Chemically different kinds of keratin (the main proteins inside the cells of the hair shaft) as well as other proteins may also contribute to differences in cell-size and -shape, and in that way could influence the degree of curliness of hair.
References: D.P. Harland et al., Journal of Experimental Biology, vol. 221, part 6 (March 22, 2018); Online Mendelian Inheritance in Man (OMIM), #139450.
11 April 2018
3. Is IQ inherited? – Answer: In one sense, IQ (intelligence quotient, measured with various kinds of test) must be inherited, in the same way that human vision or human kidney function is inherited. There would be no IQ at all without human genes, passed from parents to offspring, allowing humans to have intelligence and to take the tests.
What is usually meant by the question, however, is this: Are IQ differences between people the result of differences in their genes, or differences in the environments they have experienced? Here the answer is: IQ differences between people is affected both by gene differences and by environmental differences.
Detailed gene surveys of people with different IQs have shown that there are many variable genes affecting performance on IQ tests. The role of gene differences also shows up in twin studies, in which identical twins (both sharing the same genes) have more-similar IQs than do fraternal twins (who on average share only half their genes). The conclusion from studies in many different countries is that differences in IQ scores in the general population are the result both of gene differences and of environmental differences, about equally.
This conclusion (“equal effects of gene differences and environmental differences”), however, depends on the circumstances. It wouldn’t apply to, say, a group of children all of whom had the best health care, the best parents, the best schools. In this case, because the environments are optimal or near-optimal for all the children, whatever IQ differences were found among them would be mostly the result of differences in their genes.
Neither would the general conclusion apply to two groups of children, one of which regularly experienced poor nutrition, dangerous neighborhoods, limited access to health care, and poor schools, compared with other children from an affluent segment of society. Here the difference in performance on IQ tests between the two groups of children would be mostly the result of the difference in their environments. The environmental differences would swamp out whatever gene differences might exist between the two groups of children.
In determining IQ differences, the approximately equal effects of gene differences and environmental differences will apply for groups of people having the usual variability in the genes they were born with, and exposed to the normal range of environments.
4. Are phobias caused by genes? – Answer: In some people, the tendency to develop a phobia – a long-lasting, irrational, unreasonable, uncontrollable and excessive fear, severe enough to interfere with normal living in some situations – can be heightened by genes. The development of a phobia, as with most mental traits, often depends on both a certain set of environmental circumstances and a certain set of genes affecting the mind’s response to particular objects, animals, or situations (such as triskaidekaphobia, an abnormal fear of anything related to the number 13; musophobia, extreme fear of mice; agoraphobia, excessive fear of open spaces; claustrophobia, excessive fear of closed spaces; and glossophobia, disproportionate fear of speaking in public).
Phobias usually develop in childhood or adolescence. It has been estimated that in their lifetime at least 10% of the population has suffered or is suffering from some kind of phobia, women perhaps somewhat more frequently than men. The origin of phobias is not well understood. Early traumatic experiences and fears learned from parents often play a role. Some phobias, such as fear of heights (acrophobia), fear of snakes (ophidiophobia), and aichmophobia (fear of needles and other sharp or pointed objects), may be exaggerated forms of fears that are not totally irrational, and might have an evolutionary basis.
Specific forms of genes carried by some people and not by others may partly explain why some people develop phobias and others don’t. The evidence for this is that two identical twins (who share 100% of their genes) develop aphobia (and often the same phobia) more often than do two fraternal twins (who share on average only 50% of their genes). The specific genes involved are not known.
Phobias can sometimes (although not always) be ameliorated by mild or repeated exposures to the fear-causing stimulus, or other kinds of behavioral/cognitive therapy. Phobias can sometimes also be managed with the help of medication.
26.xii.15 Thanks to Ron Newman for this question.