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12 The Discovery of Sex in Microorganisms

Elof Axel Carlson Indiana University Press ePub

When Anthony van Leeuenhoek observed the animalcules, as he called them, from different dips of water or from his own body, he did not discuss how they formed. Most of his contemporaries would have said that they formed from spontaneous generation. The idea is as old as written thought. Aristotle believed in spontaneous generation, and so did anyone watching rotting food or meat swarming with maggots. Before Rudolph Virchow and Robert Remak’s cell doctrine, biologists did not think of life coming from preexisting life. At least they conceived the process as far back as life goes: Genesis for the pious; after Charles Darwin, some sort of event that led to the formation of the first living cell; or after H. J. Muller, the formation of the gene, the first replicating molecule that could copy its errors.

Microscopy flourished in the last half of the nineteenth century. It spun off the field of histology in medical schools and the field of cytology that led to inquiries about heredity. It was a necessary tool for the field of microbiology that flowed from germ theory. Louis Pasteur (1822–1895) and Robert Koch (1843–1910) introduced the germ theory of infectious diseases in the 1870s and 1880s. It revealed even smaller organisms than those seen by Robert Hooke and Leeuenhoek. Pasteur and Koch’s theory brought microscopy back to the medical school to study infectious diseases caused by bacteria and other microorganisms. By the end of the nineteenth century, scientists inferred the existence of even smaller organisms, which slipped through filters that barred passage of bacteria. In 1892, the first virus, tobacco mosaic virus, was identified.1

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5 The Descriptive Embryology of Male and Female Development

Elof Axel Carlson Indiana University Press ePub

The study of embryology was extremely limited until the 1860s, when several techniques came together. One was the development of achromatic lenses, which allowed scientists to observe cells or other small objects without the confusion of chromatic aberration and spherical aberration. Chromatic aberration involves the breaking up of white light into a rainbow of concentric colors around an object. Spherical aberration is even worse because there is no central focus and competing points of convergence lead to a blurred image. Joseph Jackson Lister (1786–1869), whose more famous son, Joseph Lister (1827–1912), introduced antiseptic surgery, provided the solution.1

Like his father, Lister was a wine merchant. They were Quakers and fairly pious. Lister worked after hours on his interest in natural history. When he took up microscopy, he found the interference with sharp images annoying and switched to making his own lenses. Lister found that dissolving lead and other salts into glass changed the density within these glasses, which yielded different focal lengths when he made lenses from them. He eventually worked out a combination of two layers of molten glass (crown glass and flint glass), one correcting the other for both chromatic and spherical aberration. The resulting achromatic lenses revolutionized both astronomy (allowing bigger telescopic lenses) and biology (allowing compound microscopes that would multiply an object up to 2000 times. He began his experiments on lenses in 1824 and found a suitable achromatic lens in 1826, which he refined until publishing his findings in 1830.

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14 Dosage Compensation and the Sex Chromosomes

Elof Axel Carlson Indiana University Press ePub

Calvin Bridges and Thomas Hunt Morgan discovered the existence of dosage differences on the X chromosome of fruit flies when comparing the allele of white eyes called eosin to that of the allele of white eyes called apricot. They called the phenomenon bicolorism, but did not make a generalization about it. In a stock of eosin flies, females had a darker eye color than males. In a stock of apricot flies, the eye color of the male and the female was the same. Eosin arose in a bottle of white-eyed flies as a solitary male fly. It was interpreted as a partial reverse mutation from white to eosin. About a decade later, in 1926, Curt Stern (1902–1981) discovered a mutation called bobbed bristles. It was the first genetic character found on the Y chromosome in fruit flies that was not associated with fertility.1 As it turns out, the shorter and slightly elevated bristles are associated with a gene on both the X and the Y chromosome. This made the gene behave like an autosomal recessive. Normal males and females had two doses, but XO males had a single dose and XXY fertile females had a triple dose. Stern noted that as the number of bobbed alleles increases, there is a normalizing effect.

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18 The History of Homosexuality

Elof Axel Carlson Indiana University Press ePub

All human behavior is subject to the judgment of others. As children, we are judged by our parents, teachers, and playmates. Some behaviors are approved and admired; others are condemned and sometimes punished. That has been the history of behavior concerning table manners, dressing, grooming, reliability, dishonesty, theft, selfishness, generosity, cursing, bullying, flirting, and just about anything we do. Both culture and religion have their dos and don’ts. Those values change from generation to generation, and they are different in different countries and regions of countries. Almost all cultures condemn violent behavior toward those who are not designated by the state as legitimate objects for attack. We punish perjury, theft, fraud, treason, blackmail, piracy, and many other behaviors as crimes, and regulate them with laws. Most industrial nations no longer regard some crimes of the past as crimes today. At one time, blasphemy was a capital crime. Until the 1920s, it was a crime for a physician in the United States to offer medical advice on birth control. Until the 1950s, it was a crime for a white person to marry or live with a black person. Until the 1970s, a physician who carried out an abortion committed a crime.

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11 The Balance Theory of Sex Determination

Elof Axel Carlson Indiana University Press ePub

From 1907, when Thomas Hunt Morgan began working on fruit flies, until 1915, he and his students believed that their sex chromosome composition was 2N = 8,XX for females and 2N = 7,XO for males because they had misinterpreted a paper that Nettie Stevens wrote in 1907. Once Morgan and his students realized that Drosophila melanogaster used the XX female and XY male system for sex determination, they had to reconcile the role of the Y chromosome in sex determination.1 Since it was well known from Edmund B. Wilson’s and Stevens’s work that some Diptera had XO males and others had XY males, they concluded that the Y could not be playing a role in the sex determination of males.

That inference was reinforced when Calvin Blackman Bridges (1889–1938) discovered a phenomenon he called nondisjunction, the topic on which he wrote his PhD dissertation, which was published in 1916.2 Bridges found an unexpected appearance of a white-eyed male in a cross that should have given red-eyed males. If one parent is a white-eyed male and the female parent is red eyed, all the progeny should be red eyed. When Bridges tried to mate the white-eyed male, he found it was sterile. He also found that if he did a cross with a white-eyed female and red-eyed male, the offspring should be white-eyed sons and red-eyed daughters: a distribution that the laboratory referred to as crisscross inheritance. But Bridges found a female that was white eyed on some occasions. That exceptional female was fertile, and when mated to a red-eyed male she gave an unusual distribution of progeny: about eight percent of the offspring being of an unexpected kind with respect to their eye color and sex.

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